Aged blood factors decrease cellular responses associated with delayed gingival wound repair
Aged blood factors decrease cellular responses associated with delayed gingival wound repair
MarÂõa Paz SaldÂõas 0 1
Christian FernaÂ ndez 0 1
Alejandra Morgan 0 1
Catalina DÂõaz 0 1
Diego Morales 0 1
FabiaÂ n Jaña 1
Alvaro GoÂ mez 0 1
Alonso Silva 0 1
Fernanda Briceño 0 1
Alejandro OyarzuÂ n 1
Felipe Maldonado 1
Oscar Cerda 0 1
Patricio C. Smith 1
MoÂ nica CaÂ ceres 0 1
0 Program of Molecular and Cell Biology, Institute of Biomedical Sciences, Faculty of Medicine, Universidad de Chile , Santiago , Chile , 2 Universidad de Ays eÂn , Coyhaique , Chile , 3 Faculty of Dentistry, Universidad Finis Terrae , Santiago , Chile , 4 Department of Anesthesia, Faculty of Medicine, Hospital ClÂõnico de la Universidad de Chile , Santiago, Chile, 5 Millennium Nucleus of Ion Channels-Associated Diseases (MiNICAD), Santiago , Chile , 6 School of Dentistry, Faculty of Medicine, Pontificia Universidad Cat oÂlica de Chile , Santiago , Chile
1 Editor: Philip C. Trackman, Boston University Henry M Goldman School of Dental Medicine , UNITED STATES
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: This work was supported by National
Fund for Science and Technology (Fondecyt) Grant
11140064 (MC), UINICIA 44051 Grant from
Universidad de Chile (MC) and Fondecyt Grant
Competing interests: The authors have declared
that no competing interests exist.
Aging is a gradual biological process characterized by a decrease in cell and organism
functions. Gingival wound healing is one of the impaired processes found in old rats. Here, we
studied the in vivo wound healing process using a gingival repair rat model and an in vitro
model using human gingival fibroblast for cellular responses associated to wound healing.
To do that, we evaluated cell proliferation of both epithelial and connective tissue cells in
gingival wounds and found decreased of Ki67 nuclear staining in old rats when compared to
their young counterparts. We next evaluated cellular responses of primary gingival fibroblast
obtained from young subjects in the presence human blood serum of individuals of different
ages. Eighteen to sixty five years old masculine donors were classified into 3 groups:
ªyoungº from 18 to 22 years old, ªmiddle-agedº from 30 to 48 years old and ªagedº over 50
years old. Cell proliferation, measured through immunofluorescence for Ki67 and flow
cytometry for DNA content, was decreased when middle-aged and aged serum was added
to gingival fibroblast compared to young serum. Myofibroblastic differentiation, measured
through alpha-smooth muscle actin (α-SMA), was stimulated with young but not
middleaged or aged serum both the protein levels and incorporation of α-SMA into actin stress
fibers. High levels of PDGF, VEGF, IL-6R were detected in blood serum from young
subjects when compared to middle-aged and aged donors. In addition, the pro-inflammatory
cytokines MCP-1 and TNF were increased in the serum of aged donors. In old rat wound
there is an increased of staining for TNF compared to young wound. Moreover, healthy
gingiva (non injury) shows less staining compared to a wound site, suggesting a role in wound
healing. Moreover, serum from middle-aged and aged donors was able to stimulate cellular
senescence in young cells as determined by the expression of senescence associated
beta-galactosidase and histone H2A.X phosphorylated at Ser139. Moreover, we detected
an increased frequency of γ-H2A.X-positive cells in aged rat gingival tissues. The present
study suggests that serum factors present in middle-aged and aged individuals may be
responsible, at least in part, for the altered responses observed during wound healing in
The proportion of people over 60 years old is growing faster than any other age group. By
2050, the number of people over 60 years is projected to be five times than in 1950 [
is associated with a decline in health, and altered gingival wound healing is one of the impaired
processes found during aging [
During wound healing, coagulation is activated through the formation of a fibrin clot that
serves as a temporary matrix, providing a mesh of fibrin and a reservoir of cytokines and
growth factors like PDGF, TGFβ1 and 2, EGF, VEGF, HGF, FGF-2, RANTES, MIP-1α and
]. This group of early growth factors provides chemotactic cues to recruit inflammatory
cells into the wound site, initiates reepithelization and the migration and
proliferation/activation of fibroblasts . Three to five days after injury, the formation of the granulation tissue
begins, with the migration and activation of fibroblasts, endothelial cells and macrophages
into the blood clot [
]. About 7 to 10 days after wounding, the granulation tissue becomes
hypercellular containing abundant fibroblasts and endothelial cells. During this process
fibroblasts are differentiated into active myofibroblasts, a transient cell population involved in the
synthesis and organization of the newly formed extracellular matrix and wound contraction
]. Importantly, myofibroblast differentiation is important for matrix deposition and
organization during wound healing. To do that, myofibroblast express a new actin isoform known as
α smooth muscle actin that reinforces the wound remodeling capacity of these cells [
the parabiosis animal model, that connects the circulatory system of young and old animals,
previous studies have described an improvement in the repair of aged bone fracture [
muscle lesions in aged conditions [
] and reversion of age related impairments in cognitive
functions and synaptic plasticity in mice [
]. These studies have suggested that growth factors
present in the blood of aged subjects may play a detrimental role in wound healing.
Interestingly, the role of blood-derived factors in oral wound healing remains unknown.
The present study was designed to evaluate whether factors present in the serum of aged
and middle-aged subjects may partially reproduce delayed wound-healing responses
associated with aging.
Material and methods
Primary cultures of human gingival fibroblasts (HGF) were obtained from healthy gingival
tissue surrounding bicuspids obtained from non-smoking, systemically healthy individuals.
Periodontal examination demonstrated sites with probing depth <4 mm, no loss of attachment
and no bleeding on probing. Primary cultures of Human Gingival Fibroblast (GF) were
established by the explant method and were cultured in DMEM (Gibco BRL, Grand Island, NY)
containing 10% fetal bovine serum (FBS) (Hyclone laboratories Inc, Logan, Utah) and
antibiotics as previously described . Tissue explants were obtained from clinically healthy
gingiva of 5 individuals (15±25 years old) after the extraction of third molar. Tissue samples were
harvested with the informed consent of the patients. The protocol for tissue obtainment was
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approved by the Ethical Committee, Faculty of Medicine, Universidad de Chile (095±2014).
All experiments were performed using cells expanded between passages three and nine.
Serum collection was acquired by coagulating 10 mL of blood at 37ÊC for 1 hour and then
centrifuged at 2500 rpm during 10 min. The supernatant corresponds to serum. We used
serum from 45 non-smoker healthy male volunteers from different ages (18 to 70 years old),
with no acute or chronic infectious diseases, or any clinical disorders or chronic drug intake.
All donors signed an informed consent in agreement to the Ethical Committee, Faculty of
Medicine, Universidad de Chile. All these procedures were performed in accordance to the
protocol 095±2014. None of the donors were from a vulnerable population and all donors
provided written informed consent that was freely given. We defined three groups of study:
ªyoungº (between 18 and 22 years old) (n = 21), ªmiddle-agedº 30±48 years old (yo) (n = 13)
and ªagedº or ªelderlyº (50 or more years old) (n = 11). The average and standard deviation of
age of these 3 group was 20.16 ±1,51 young, 34.83 ± 5.98 middle-aged and 57.578 ± 5.25 aged
years old respectively.
Wound healing studies. Five young (2 months old) and five old (18 months old) male
Sprague-Dawley rats were used for wound healing studies, Full-thickness excisional wounds
were made in the palatal gingiva close to the first and second upper molars (1.0 mm x 3 mm)
with the aid of a periodontal probe (Hu-Friedy) as previously described [
]. Animal procedures
were conducted in accordance to the Administrative Panel on Laboratory Animal Care at
Universidad de Chile (CBA 0706) and following the ARRIVE (Animal Research Reporting of in
vivo Experiments) guidelines for animal experimentation [
]. During aging of the rats and the
wound healing assay we maintained 2 rats for cage with light/dark cycle and food at libitum.
After 7 days of wound repair, rats were anesthetized with 2% isofluorane administered using a
nasal mask and then animals were sacrificed by an intracardiac euthanasia (T61) that contained
(Embutramide 0.2 g, Mebezonium iodide 0.05 g y Tetracaine hydrochloride 0,005g for 1 mL)
Tissues were fixed in 10% buffered formalin, decalcified in 10% formic acid and were
stained with Masson Trichrome and scanned using a Nanozoomer -XR digital slide scanner
C12000 (Hamamatsu Photonics KK, Hammamatu city, Japan). For immunostaining, 5μm
cross sections were treated with Tris-EDTA pH = 9 for 30 min at 80ÊC, blocked during 2 h
with 10% calf serum and Triton-X100 0,3%, incubated with anti-Ki67 (D3B5,Cell Signaling
technology, Danvers, MA, USA) and anti-vimentin (V6389,Sigma, St. Louis, MO, USA)
antibodies. Primary antibodies were detected with anti rabbit IgG(H+L) and anti mouse-IgG1
conjugated with alexa fluor 488 and alexa fluor 555 secondary antibodies, respectively
(Invitrogen, Carlsbad, CA, USA). Images were acquired with a spinning disk Olympus IX81
microscope. No primary antibody was used as a negative control. Nuclei were stained with Hoechst.
For TNF staining and phospho Histone H2A.X (Ser139) we treated 5μm cross section with
buffer citrate (10mM citric acid, 0,05% Tween-20, pH = 6), for 30 minutes at 90ÊC. Then,
treated during 20 minutes with H2O2 at 3%v/v. Blocked with 10% calf serum and 0,3%Triton
X-100 during 2 hours, incubated with anti TNF (ab6671, Abcam, Cambridge, MA,USA) or
pSer139 H2A.X (clone JBW301,Merck) overnight at 4ÊC. In negative control sections, primary
antibody was replaced by non immune calf serum. Primary antibody was detected using RTU
biotinylated antibody universal and mouse/rabbit IgG during 30 minutes at room temperature
(BP-1400, Vector Laboratories, Burlingame, CA, USA). Then, we used Vectastain Elite ABC
kit system (PK-6100, Vector, Burlingame, CA, USA) during 30 minutes at room temperature.
After 3 washed, immunoreactive signal was detected with DAB Peroxidase substrate (SK-4100,
Vector Laboratories). After immunohystochemical procedures, Hematoxilyn Delafield was
used for counterstaining.
To quantify wound closure tissue sections were stained with Masson trichrome and images
were scanned using a Nanozoomer digital slide scanner and analyzed by the NDP.view
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software version 220.127.116.112. This software allows us to quantify the area of the granulation tissue
expressed as mm2. The amount of collagen (detected through the Masson Trichrome stain) was
quantified for each specimen by measuring the area of collagen as μm2 in the granulation tissue
(area of the cells were excluded) and expressed as percentage of the total area of granulation
tissue. For TNF stained we selected at least 5 ROI of 55 μm2 in the wound area, in this selection
area we obtained the minimal intensity and the mean intensity of the chromogenic stain.
1 mL of blood were coagulated at 37ÊC for 1 hour and then centrifuged at 2500 rpm during
10 min. The supernatant correspond to the blood serum, aliquots were stored at -80ÊC until
use. Rat blood serum cytokines were evaluated using rat cytokine profile antibody array (ARY
008, R&D system Minneapolis MN, USA).
Cells were grown on coverslips, fixed with 4% (w/v) paraformaldehyde, blocked, and
incubated with primary anti Ki67 antibody (D3B5,Cell Signaling technology, Danvers, MA, USA)
used as a marker for proliferation and alpha-Smooth Muscle Actin alpha (α-SMA) (A2547,
Sigma, St. Louis, MO, USA) as myofibroblasts differentiation marker. Primary antibodies were
detected with Alexa-conjugated secondary antibodies (Invitrogen). F-actin was stained with
Alexa-Fluor-555-phalloidin (Invitrogen Molecular Probes, Carlsbad, CA, USA) and DNA was
stained with Hoechst (Sigma, St. Louis, MO, USA). Images were acquired with a spinning disk
Olympus IX81 microscope.
Cell cycle analysis
Fifty thousand cells were incubated in DMEM for 16h. Then, cells were treated with 10% (v/v)
serum from volunteers of different ages for 24 h. Cells suspensions were fixed with methanol
overnight. Samples were centrifuged and incubated with 40 μg/mL propidium iodide (Sigma,
St. Louis, MO, USA) and RNAase A (100 μg/mL). Cells were then analyzed by flow cytometer
(FACSCanto, Becton Dickinson)
Quantification of blood factors. To evaluate MCP-1, PDGF, HGF, TNF, VEGF and IL-6R,
serum samples were diluted 5 times and quantified by ELISA multiplex array (Quansys,
biosciences). TGFβ1 was diluted 5 times in PBS, treated with HCl 1M during 10 min, neutralized with
NaOH 1N and analyzed by ELISA affymetrix (eBioscience, San Diego, CA, USA.). Cholesterol
was measured with an enzymatic method Colestat liquid line (Wiener lab, Rosario, Argentina).
GF were incubated during 72 h with 10% (v/v) serum from volunteers of different ages. Cells
were lysed with a buffer containing 50 mM Hepes pH 7.4, 150 mM NaCl, 2 mM MgCl2, 2 mM
EGTA, 1% v/v Triton X-100, 10% v/v glycerol, 2 mM PMSF, 2 mg/mL pepstatin, 2 mg/mL
leupeptin, and 1 mM orthovanadate at 4ÊC. Proteins were resolved by SDS-PAGE and transferred
to PVDF membrane (PerkinElmer Life Sciences, Boston, MA). Membranes were exposed to
primary antibodies against α-SMA (Sigma) and β-tubulin (PA5-16863, Thermo Scientific
Rockford, IL, USA), and secondary antibodies coupled to horseradish peroxidase (KPL,
Gaithersbury, MD, USA) and developed (ECL kit, Amersham Biosciences, Piscataway, NJ).
Detection of senescence associated beta-galactosidase (SA-βgal)
GF were incubated for 3 days with 10% v/v serum from young, middle-aged and aged
volunteers. Cells were washed in PBS and fixed with 2% w/v paraformaldehyde and 0,2% v/v
glutaraldehyde for 5 minutes. Then, stained with solution 40 mM citric acid/Na phosphate buffer,
4 / 16
5mM K4[Fe(CN)6] 3H2O, 5mM K3[Fe(CN)6], 150 mM NaCl, 2mM MgCl2 and 1mg/mL X-gal
(Bioline,Taunton, MA) during 24 hours [
] (Debacq-Chainiaux, et al, 2009). Nuclei were
stained with MayerÂs Hematoxylin. As a positive control of cellular senescence, cells were
exposed to 100μM H2O2 for 1 h and then treated with 10% FBS for 3 days.
Statistical analysis. All experiments were performed at least four times on separate
occasions using cells from 5 different donors and at least 8 blood different donors. Statistical
analysis was performed using the Mann-Whitney and Kruskal Wallis non-parametric tests. The
statistical software Prism 5.0 from GraphPad was used (La Jolla, CA). In all analyses, p<0.05
was considered to indicate statistical significance.
Impaired wound repair and proliferation in old rats
Wound healing was evaluated after 7 days of gingival injury. We found a significant delay in
wound closure in old rats (Fig 1A and 1B). Young rats show an increase in the area of
tion tissue compared with old rats (0.771± 0.037 versus 0.126 ±0.012 mm .) Using the Masson
trichrome staining we determined that collagen filled 41% and 2.1% of the lesion of young and
aged wounds respectively. Moreover, we observed an increase of cellularity (nuclei in purple
color at the connective tissue) in young rats (Fig 1A). We also evaluated whether changes in
cell proliferation, measured through Ki67 staining, were associated with these responses. We
found an increase of positive cells in young rats compared to old rats (52.75 versus 16.25 cells).
Moreover, we found a 3 fold increase of positive cells for ki67 staining in the connective tissue
when we compared young wounds to their aged counterparts, ranging the counts of cells from
13 cells in young rats versus 3.25 cells in old rats (Fig 1C). Vimentin, a cell marker of
intermediate filament was used to identify mesenchymal cells (Fig 1C).
Serum from middle-aged and aged donors do not induce cell proliferation in GF
We next determined whether cell proliferation defects detected in aged rats were related to
serum derived-factors. Therefore, gingival fibroblasts derived from young subjects were
exposed to blood serum obtained from the three age groups under study. GF were
synchronized for 16h in DMEM without serum and incubated with 10% blood serum obtained from
young (18±22 yo) middle-aged (30±48 yo) and aged (50±65 yo) volunteers for 24 h. As shown
in Fig 2B the proportion of Ki67 positive/nuclei were 47.02 ± 4.31%, 16.93 ± 3.24%, 13.48 ±
2.28% for the young, middle-aged and aged groups respectively. We next performed a more
specific assay to evaluate the proliferative response of cells. Evaluation of the proportion of
cells in the S phase of the cell cycle determined that 8.85 ± 1.7%, 36.6 ± 1.54%, 24 ± 1.7%,
20.5 ± 1.32% were present in the control, young, middle-aged and aged group respectively. Fig
2C shows a representative curve of GF treated with one serum for each group. These results
show that the increase in cell proliferation depends on serum donor age, whereas the
incubation with young serum increased cell proliferation.
Serum from middle-aged and aged donors stimulate cellular senescence
by expression of SA-βgal
Salient features of the senescent cells are, the arrest of cell cycle, increased in size and the
expression a senescent±associated β galactosidase (SA-βgal) which partly reflects the increase
in lysosomal mass senescence growth [
]. We evaluated whether serum from different ages
might contain factors that may promote the development of cellular senescence. Therefore,
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Fig 1. Old rats present impaired wound healing compared to young rats. Full-thickness wounds were made in the palatal gingiva. A.
Sections of wounded gingiva from young and aged rats were stained with Masson Trichrome at day 7 post wounding. Images were
scanned with nanozoomer at 2,5X, 5X and 20X. Scale bar:400μm. B Quantification of area granulation tissue in wounded area. C
Immunostained for Ki67 (green) and vimentin (red). Scale bar 50μm C Quantification of positive cells for Ki67/total cells in epithelial and the
connective tissue in the wound area. Arrowhead indicated focus of collagen. Bars indicate standard error. All assays were performed in
quadruplicate. Asterisks indicate statistically significant differences (p = 0.0285 for Epithelial Tissue) and p = 0.00286 for Connective
Tissue. n = 5.
GF were incubated with 10% serum from different ages during 3 days. The frequency of
senescent cells in culture (positive for SA-βgal) increased when cells were exposed to serum from
aged subjects ranging from 0.38 ± 0.21% (10% FBS;control), 0.51 ± 0.30% (young serum),
0.98 ± 0.55% (middle-aged serum), 1.15 ± 0.52% (aged serum) or positive control (6.5 ± 1.1%;
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Fig 2. Middle-aged and aged serum do not induces GF proliferation. A Representative images of Immunofluorescence for Ki67 and Hoechst, GF treated
with young serum (18 yo), middle-aged serum (30 yo) and aged serum (65 yo). B Graph indicated the quantification of ki67(+)cells/total cells. C Flow
cytometry analysis showed that young serum promotes the proliferation of GF, graph of PI versus count of cells, control (green), young serum (red),
middleaged serum (gray) and aged serum (black). Asterisks indicate statistically significant differences between control and young serum treatment p = 0.001. Bars
indicate standard error. All assays were performed in quadruplicate. (n = 8 young, n = 8 middle-aged, n = 8 aged).
100μM H2O2) (Fig 3). Moreover, we analyzed the distribution of one of the major trigger of
cell senescence, phosphorylation of Ser139 of histone H2A.X [
]. Using this cell marker we
observed an increase level in γ-H2A.X in cells treated with middle-aged and ages serum (Fig
3B). In S2 Fig we show significantly increases of γ-H2A.X foci-positive cells, presumably
fibroblast in the tissue close to the wound in old rats than in young tissue.
Serum from middle-aged and aged donors do not stimulate myofibroblastic differentiation
Myofibroblasts play a fundamental role in collagen secretion and matrix remodeling [
Therefore, we evaluated whether myofibroblastic differentiation was affected by serum derived
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Fig 3. Middle-aged and aged serum induces some senescent cells. A Representative images of SA-β of control cells, cells treated with 100μM H2O2,
10% v/v young, middle-aged and aged serum. Graph shows the quantification of SA-βgal positive cells versus total cells stained with MayerÂs Hematoxylin.
Arrow head indicated positive cell for SA-β. B Immunofluorescence of histone H2A.X phosphorylated at Ser139 and DNA stained by Hoechst. All assays were
performed in quadruplicate (n = 8 young, n = 8 middle-aged, n = 8 aged).
from different donors. GF were treated with 10% serum from different ages during 72 h.
Using, immunofluorescence we observed that in GF treated with young serum, α-SMA was
distributed in association with actin stress fibers (Fig 4). However, α-SMA was not
incorporated into the stress fiber in cells treated with middle-aged and aged serum (Fig 4A). This
response was quantified in the graph shown in Fig 3B, demonstrating a significant increase in
the proportion of cells with α-SMA incorporated into actin stress fibers in cells exposed to
serum from young donors. Furthermore, the total α-SMA protein levels were increased in cell
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Fig 4. Young serum induces differentiation to myofibroblast with α-SMA incorporated into stress fiber. A Immunofluorescence of α-SMA (green), F
actin (red) and DNA with Hoechst (blue) of GF treated during 72 hours with 10% young serum, middle-aged serum and elderly serum. B Graph indicated the
quantification of α-SMA incorporated into stress fibers/ α-SMA (+) cells. Asterisks indicate statistically significant differences between control and young
serum treatment p = 0.0121 (n = 9 young, n = 9 middle-aged, n = 8 aged) in 4 different experiment. C Serum-starved cells were stimulated with serum from
different ages for 72 h, α-SMA and GAPDH were analyzed through Western-blot of the cell lysates (n = 7 young, n = 7 middle-aged, n = 6 aged). Bars indicate
standard error. Asterisks indicate statistically significant differences (p = 0.0356). Scale bar 10μm.
lysates exposed to young serum were compared to control, middle-aged or aged serum (Fig
Human blood factors related to wound healing change during aging
We then hypothesized whether serum from subjects of different ages may show differences in
the concentration of cytokines and growth factors that may explain the above-described
responses. Therefore, MCP-1 and IL6R protein levels were evaluated in the serum of these
volunteers. Monocyte Chemoattractant Protein-1 (MCP-1) is a chemokine that regulates the
migration and infiltration of monocytes, memory T lymphocytes and natural killer (NK) [
Soluble IL-6 receptor (IL-6R) forms a ligand-receptor complex with IL-6 to stimulate
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Fig 5. Blood soluble factors related to wound healing vary with the age. A Quantification of MCP-1, TNF and IL-6R.B Quantification of
growth factors PDGF-BB, VEGF, TGFβ1 and HGF. C Graph of the levels of total cholesterol. Asterisks indicate statistically significant differences.
Young (n = 21), over 50 yo (n = 10). The group in between ages was middle-aged 30±48 yo (n = 13).
proliferation, differentiation and inflammatory processes [
]. Serum concentration of MCP-1
was found to increase with age from 108.55 ± 8.85 pg/mL (young) 152.78 ± 13.35 pg/mL
(middle-aged) to 155.87 ± 13.54 pg/mL (aged). Whereas IL-6R was found at decreased levels in
serum of aged subjects ranging from 4981 ± 392 pg/mL (young), 3740 ± 110.7 pg/mL
(middleaged), 4005 ± 234.5 pg/mL (aged serum). Also, Tumor Necrosis Factor alpha (TNF) a potent
inflammatory cytokine expressed during the inflammatory phase of wound healing [
found an increase in TNF protein levels with increasing age with values ranging from 5.92 ±
1.78 pg/mL (young serum), 27.52±5.6 pg/mL (middle-aged) and 98.29 ± 20.6 pg/mL (aged
serum) (Fig 5A). We next evaluated growth factors involved in cell proliferation [
angiogenesis in the granulation tissue such as Platelet Derived Growth Factor (PDGF) and
Vascular Endothelial Growth Factor (VEGF). We found that PDGF decreased with the age
from 507.76 ± 38.78 pg/mL (young serum), 447.4 ± 54.8 (middle-aged) and 283.68 ± 27.36 pg/
10 / 16
mL (aged serum). VEGF levels decreased with the age from 61.259 ± 5.3 pg/ml (young serum)
to 53.097 ± 6.99 pg/mL (middle-aged serum) and 37.01± 5.39 pg/mL (aged serum). In addition
we evaluated Transforming Growth Factor beta 1 (TGFβ1), responsible for myofibroblastic
differentiation. Surprisingly, we did not found differences in the serum levels for this factor
with the following values for young (10.64 ± 2.3 ng/mL), middle-aged (10.55 ± 1.53 ng/mL)
and aged (9.81 ± 2.313 ng/mL) samples (Fig 5B). We finally evaluated Hepatocyte Growth
Factor, not finding significant differences between these groups, 288.63 ±16.8 for young serum,
283.6 ± 8.15 for middle-aged and 351.5 ± 10.121 pg/mL for aged group. These results confirm
that not all growth factors were modulated by age. Cholesterol levels measured as a control,
were detected at increased levels in middle aged subjects when compared to young serum, but
in average all ages were less than 2 g/L (Fig 5C).
Serum from old rat present inflammatory cytokines
To evaluate the presence of pro inflammatory cytokines in rat blood serum we realize a
proteome profile cytokine antibody array, in which old blood serum have higher levels of CINC-1,
IL-1α, SICAM, CX3CL1, MIP-1α compared to young serum. LIX and RANTES were found at
similar levels. Unfortunately, we could not detect TNF by this method.
Similar to human blood serum from middle aged and aged, blood serum from old rats
contain several cytokines related to inflammation like MIP1α that is a member of the C-C family
of chemokines that exhibit a variety of proinflammatory activities and macrophages are a rich
source of MIP1alpha [
], also contain cytokine-induced neutrophil chemoattractant 1
(CINC-1) that play critical roles as a mediator of inflammatory reactions with neutrophil
infiltration in rats [
] and IL-1α that is a potent inflammatory cytokine that activate the
inflammatory process. [
One of the cytokine that increased in human blood serum during aging is TNF. We
evaluated locally the expression of TNF in wound from young and old rats (Fig 6C). Wound from
old rats present higher staining of TNF compared to wound from young rats (Fig 6C).
Moreover, healthy gingiva (non injury) shows less staining compared to a wound site (Fig 6D),
suggesting an important role of TNF during wound healing. Using the software NDP analysis, we
observed that the minimal intensity of the selected ROI in wound from young rats was
63.6 ± 3 versus 92 ±3.5 in old rats. Moreover, the mean intensity in young rats was 122 versus
138 founded in old rats. This analysis suggests that the expression of TNF was higher in old
rats compared to young rats.
Interestingly, young gingival fibroblast treated with 10% young serum and 300 pg of TNF
during 3 days, show that the addition of TNF to young serum increased of cellular senescence
as shown in S1 Fig.
The identification of factors enriched in young blood or lost in old blood that can improve
wound healing is a key research goal.
The findings of the present study allow us to propose that factors found in the serum of
middle-aged and aged subjects may contribute to delayed wound healing by decreasing cell
proliferation and myofibroblastic differentiation and by stimulating cellular senescence. All these
responses may impact wound healing since they are necessary to augment the amount of
cells needed for tissue repair and for the secretion and organization of collagen in tissues [
Moreover, senescent cells have been associated with impaired wound healing as well [
Therefore, serum derived factors might be responsible, at least in part, for delayed wound
healing responses associated with aging.
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Fig 6. Old rat serum present higher levels of pro-inflammatory cytokine. A Representative image of the cytokine proteome array from young and old rat
serum B Graph indicated the quantification of the pixel mean density of each cytokine. C TNF distribution in wound from young and old rats after 7 days of
repair 5X, 40X and inset of 100X.D TNF distribution in non wound gingiva 5X (scale bar 150 um) and 40X (scale bar 50um). E Negative control 5X and 40X.
Our study suggests that aging may have an early manifestation in serum related to the
variations in some inflammatory cytokines and growth factors. These changes included an increase
in MCP-1 and TNF in the serum of aged subjects evaluated in this study and a decrease in
PDGF, VEGF and IL-6R. In addition, no changes were found in TGFβ1 and HGF protein
levels. According to these findings, the augmented levels of inflammatory cytokines might
contribute with increased levels of inflammatory cells in tissues that may delay wound repair. It is
important to consider that TGFβ-stimulated myofibroblastic differentiation is effectively
inhibited by the inflammatory cytokine TNF as described for dermal [
] and gingival
] In addition, TNF may impair wound healing in diabetes [
], suggesting that this
12 / 16
cytokine is probably implicated in delayed wound healing in different contexts. The results
described in our study suggest that increased TNF levels found in serum from middle-aged
and aged donors may be responsible for the decrease in myofibroblastic differentiation found
in cells exposed to these factors. More studies are needed to identify and quantify the amount
of TGFβ1, TNF and other relevant cytokines during wound healing in young and aged tissues.
The diminished levels of PDGF and VEGF found in the serum of middle-aged and aged
subjects might also contribute to explain the reduction in cell proliferation observed in our
study. PDGF and VEGF are also involved in cell migration [
] and angiogenesis [
Although we did not test this possibility in the present study, these assays should identify other
relevant functions putatively modulated by serum factors in aged subjects.
Previous studies have evaluated PDGF, VEGF and TGFβ1 serum levels in 18 years old
males. These determinations were similar to our findings with measurements approaching 1.7
ng/mL for PDGF, 20 ng/mL for TGFβ1 and 91.83 pg/mL of VEGF [
]. Moreover, a similar
result was obtained by Bayer et al, (2012), who found that TGFβ1 serum levels did not change
with age . Moreover, work by Weibrich et al (2002) analyzed platelet rich plasma of 203
donors between 17 and 62 years old and found no influence of gender or age on platelet count
In recent studies, Belsky et al (2015) analyzed the correspondence between chronological
and physiological ages. In that study they evaluated young adults of 38 years old, showing a
great discrepancy between chronological age and biological age [
]. These results coincide
with our observations concerning the concentration of soluble mediators present in serum in
the middle-aged group. Further studies are needed to better characterize aging within this
It has been proposed that senescent cells develop the so called senescent associated secretory
phenotype (SASP), a trait characterized by the production of growth factors, matrix
remodeling enzymes and inflammatory cytokines that include IL-6 and IL-8 among others [
]. In this
work we have observed MCP-1 and TNF are found at increased levels in the serum of aged
subjects. It is possible to propose that these inflammatory cytokines may be responsible for the
detrimental effects of middle-aged and aged serum on cell proliferation and myofibroblastic
differentiation. It is interesting to consider whether cells responsible for the secretion of these
cytokines are involved cellular senescence at some level. Moreover, our observation of the
effect of middle-aged and aged serum on the induction of cellular senescence in young
fibroblasts may also suggest that serum may contribute to the initiation of cellular senescence in
tissues. It is important to consider that in aged organisms the proportion of senescent cells may
vary between 1% to 15% [
]. Hubackova et al (2016) demonstrated that TNFα and IFN
gamma induce cellular senescence in mouse tumor cells [
]. Given our observation of
increased TNF levels in the serum of aged subjects it is interesting to propose whether this
cytokine may play a role in the induction of cellular senescence in periodontal tissues.
Interestingly, diabetes delay wound healing, which may result in limb amputation.
Enhanced levels of advanced glycation end product (AGEs) and TNF are associated with these
phenomena. Impaired wound healing in diabetic animals are improved by blocking TNF,
which reduces infiltration by proinflammatory macrophages, decreases fibroblast apoptosis
and improves collagen synthesis [
Wang et al demonstrates that γ-H2A.X immunohistochemistry is a reliable quantitate
indicator of senescence in fibroblast. Moreover, increased with age in dermis, liver and gut
]. In our data, we show increased levels of γ-H2A.X foci-positive cells in old rats
compared to young rats (S2 Fig).
The present study provides a series of observations that contribute to understand the
deficiencies detected in gingival wound healing during aging and suggests that it is important to
13 / 16
study middle-aged subjects during the early manifestations of tissue changes associated with
S1 File. Blood samples.
S1 Fig. TNF increased cellular senescence.
S2 Fig. Old rats have an increased of γ-H2A.X positive cells.
The present study was funded by a grant from the National Fund for Science and Technology
(Fondecyt) Grant 11140064 (MC), Grant from Universidad de Chile UINICIA 44051 (MC)
and Fondecyt Grant 1160518 (OC). The authors have stated explicitly that there are no
conflicts of interest in connection with this article.
Conceptualization: MoÂnica CaÂceres.
Data curation: MarÂõa Paz SaldÂõas, Christian FernaÂndez, Alejandra Morgan, Catalina DÂõaz,
Diego Morales, Alvaro GoÂmez, Alonso Silva, Fernanda Briceño, Alejandro OyarzuÂn, Felipe
Maldonado, MoÂnica CaÂceres.
Formal analysis: FabiaÂn Jaña, Oscar Cerda, MoÂnica CaÂceres.
Funding acquisition: MoÂnica CaÂceres.
Investigation: MoÂnica CaÂceres.
Methodology: MoÂnica CaÂceres.
Project administration: MoÂnica CaÂceres.
Resources: MoÂnica CaÂceres.
Supervision: MoÂnica CaÂceres.
Writing ± original draft: Patricio C. Smith, MoÂnica CaÂceres.
Writing ± review & editing: Oscar Cerda, Patricio C. Smith, MoÂnica CaÂceres.
14 / 16
10. Smith PC, Martinez J. J Dent Res. 2006; Feb; 85(2):150±5. https://doi.org/10.1177/
154405910608500207 PMID: 16434733
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