Palmitic Acid Upregulates Type I Interferon–Mediated Antiviral Response and Cholesterol Biosynthesis in Human Astrocytes

Molecular Neurobiology https://doi.org/10.1007/s12035-023-03366-z Palmitic Acid Upregulates Type I Interferon–Mediated Antiviral Response and Cholesterol Biosynthesis in Human Astrocytes Alexis Felipe Rojas‑Cruz1 Andrés Mauricio Pinzón3 · Cynthia Alexandra Martín‑Jiménez2 · Janneth González1 · George E. Barreto4 · Andrés Felipe Aristizábal‑Pachón1 · Yeimy González‑Giraldo1 · Received: 19 December 2022 / Accepted: 22 April 2023 © The Author(s) 2023 Abstract Chronic intake of a high-fat diet increases saturated fatty acids in the brain causing the progression of neurodegenerative diseases. Palmitic acid is a free fatty acid abundant in the diet that at high concentrations may penetrate the blood–brain barrier and stimulate the production of pro-inflammatory cytokines, leading to inflammation in astrocytes. The use of the synthetic neurosteroid tibolone in protection against fatty acid toxicity is emerging, but its transcriptional effects on palmitic acid–induced lipotoxicity remain unclear. Herein, we performed a transcriptome profiling of normal human astrocytes to investigate the molecular mechanisms by which palmitic acid causes cellular damage to astrocytes, and whether tibolone could reverse its detrimental effects. Astrocytes undergo a profound transcriptional change at 2 mM palmitic acid, affecting the expression of 739 genes, 366 upregulated and 373 downregulated. However, tibolone at 10 nM does not entirely reverse palmitic acid effects. Additionally, the protein–protein interaction reveals two novel gene clustering modules. The first module involves astrocyte defense responses by upregulation of pathways associated with antiviral innate immunity, and the second is linked to lipid metabolism. Our data suggest that activation of viral response signaling pathways might be so far, the initial molecular mechanism of astrocytes in response to a lipotoxic insult by palmitic acid, triggered particularly upon increased expression levels of IFIT2, IRF1, and XAF1. Therefore, this novel approach using a global gene expression analysis may shed light on the pleiotropic effects of palmitic acid on astrocytes, and provide a basis for future studies addressed to elucidate these responses in neurodegenerative conditions, which is highly valuable for the design of therapeutic strategies. Keywords Human astrocytes · Lipotoxicity · Tibolone · RNA-seq · Neuroinflammation · Lipid metabolism Introduction * Andrés Felipe Aristizábal‑Pachón 1 Departamento de Nutrición Y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá 110231, Colombia 2 Department of Neuroscience and Regenerative Medicine, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA 3 Laboratorio de Bioinformática Y Biología de Sistemas, Universidad Nacional de Colombia, Bogotá 110231, Colombia 4 Department of Biological Sciences, University of Limerick, V94 T9PX Limerick, Ireland Astrocytes are located in the entire central nervous system (CNS), playing different roles such as regulation of homeostasis and synapses; they participate in inflammatory processes and contribute to the maintenance of the blood–brain barrier (BBB), among others. Due to these important functions, astrocytes have been related to the development of several diseases such as neurodegenerative and neuropsychiatric disorders (ND) [1]. Astrocytes respond to stressful conditions to maintain and protect brain functions through a mechanism named reactivity [2]. However, when these cells become reactive, they not only can trigger protective effects, but also induce detrimental actions, which depend on specific contexts such as diseases, infections, injuries, and others [3]. It should be noted that astrocytes are heterogeneous, and they have different molecular, morphological, and functional profiles depending on the brain region [4], and 13 Vol.:(0123456789) Molecular Neurobiology most important, mouse and human astrocytes trigger different signals under stressful conditions [5]. In order to know the possible role of astrocytes in the development of ND, a large number of studies have analyzed the effects of several molecules in in vitro and in vivo models [6–9]. Nowadays, several studies are focused on assessing the effects of palmitic acid (PA), a saturated fatty acid that is part of cell membranes and is involved in several processes such as protein palmitoylation and palmitoylethanolamide synthesis [10]. The interest in this fatty acid has arisen due to high levels of PA trigger detrimental effects on the brain. For instance, it can induce the production of pro-inflammatory cytokines, reactive oxygen species (ROS), and endoplasmic reticulum stress, altering the functions of different types of cells [11]. Moreover, it has been reported an increased concentration of PA in the brains of Alzheimer’s disease (AD) patients [12]. These findings suggest that PA could be involved in the pathophysiological mechanism of ND [13], and thus, it has been used to evaluate the protective effects of different drugs, including hormones [14]. On the other hand, previous studies have found that tibolone (TIB), a synthetic steroid with estrogenic, progestogenic, and androgenic actions, protects astrocytes against the detrimental effects induced by PA. For instance, TIB attenuates inflammatory responses induced by PA [15]; it reduces oxidative damage and preserves mitochondrial functionality [16–18]. Although some genes have been explored in astrocytic cell models submitted to PA and TIB stimuli [15], to the best of our knowledge, there is no evidence of studies analyzing transcriptome-wide expression under these conditions. Regarding downstream molecules, such as proteins and metabolites, two recent studies have investigated the effects of PA and TIB treatments in in vitro experiments of astrocytes [19, 20]. Considering the relevance of PA to elucidate the role of astrocytes in relation to ND, this study analyzes the transcriptome profile of normal human astrocytes (NHA) to investigate the molecular mechanisms of lipotoxic-triggering stimuli by PA, and whether TIB might reverse its detrimental effects, according to conditions previously standardized by [18]. Interestingly, we found that PA may activate relevant genes associated with astrocyte defense responses by upregulating pathways associated with antiviral innate immunity and lipid metabolism. On the contrary, TIB has no effect in ameliorating PA-induced transcriptomic changes. Materials and Methods Cells and Culture Methods NHA cells were obtained from Lonza (Basel, Switzerland, Catalog: CC-2565). Three different batches of NHA cells: 13 (i) 0000514417 (male donor), (ii) 00005656712 (female donor), and (iii) 0000612736 (female donor) were grown at 37 °C with a humidified atmosphere and 5% C O2. The cells were seeded at 5000 cells/cm2 and kept for 12 days until they reached 80% of confluence using the astrocyte basal medium (ABM) (Lonza; Basel, Switzerla (...truncated)