Small heat shock proteins are induced during multiple sclerosis lesion development in white but not grey matter

Peferoen et al. Acta Neuropathologica Communications (2015) 3:87 DOI 10.1186/s40478-015-0267-2 RESEARCH Open Access Small heat shock proteins are induced during multiple sclerosis lesion development in white but not grey matter Laura A. N. Peferoen1*, Wouter H. Gerritsen1, Marjolein Breur1, Kimberley M. D. Ummenthum1, Regina M. B. Peferoen-Baert1, Paul van der Valk1, Johannes M. van Noort2 and Sandra Amor1,3 Abstract Introduction: The important protective role of small heat-shock proteins (HSPs) in regulating cellular survival and migration, counteracting protein aggregation, preventing apoptosis, and regulating inflammation in the central nervous system is now well-recognized. Yet, their role in the neuroinflammatory disorder multiple sclerosis (MS) is largely undocumented. With the exception of alpha B-crystallin (HSPB5), little is known about the roles of small HSPs in disease. Results: Here, we examined the expression of four small HSPs during lesion development in MS, focussing on their cellular distribution, and regional differences between white matter (WM) and grey matter (GM). It is well known that MS lesions in these areas differ markedly in their pathology, with substantially more intense blood-brain barrier damage, leukocyte infiltration and microglial activation typifying WM but not GM lesions. We analysed transcript levels and protein distribution profiles for HSPB1, HSPB6, HSPB8 and HSPB11 in MS lesions at different stages, comparing them with normal-appearing brain tissue from MS patients and non-neurological controls. During active stages of demyelination in WM, and especially the centre of chronic active MS lesions, we found significantly increased expression of HSPB1, HSPB6 and HSPB8, but not HSPB11. When induced, small HSPs were exclusively found in astrocytes but not in oligodendrocytes, microglia or neurons. Surprisingly, while the numbers of astrocytes displaying high expression of small HSPs were markedly increased in actively demyelinating lesions in WM, no such induction was observed in GM lesions. This difference was particularly obvious in leukocortical lesions covering both WM and GM areas. Conclusions: Since induction of small HSPs in astrocytes is apparently a secondary response to damage, their differential expression between WM and GM likely reflects differences in mediators that accompany demyelination in either WM or GM during MS. Our findings also suggest that during MS, cortical structures fail to benefit from the protective actions of small HSPs. Keywords: Small heat shock proteins, Multiple sclerosis, White matter lesions, Grey matter lesions Introduction Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS), affecting about 2.3 million people worldwide. Disease onset is usually first observed in young adults and it is the most common cause of non-traumatic disability in this age group [1, 2]. The pathology of MS is characterized by focal areas of inflammatory myelin damage, axonal injury and axonal loss both in white matter (WM) and * Correspondence: 1 Department of Pathology, VU University Medical Centre, Amsterdam, The Netherlands Full list of author information is available at the end of the article grey matter (GM) [3]. Actively demyelinating WM lesions that continuously emerge and regress during disease are characterised by disruption of the blood-brain barrier, marked leukocyte infiltration, and large-scale activation of microglia/macrophages. While in the GM, demyelination generally progresses with much less tissue infiltration and microglial activation [4, 5]. In addition to focal lesions of overt myelin damage, small focal clusters of activated microglia are frequently observed in the normal appearing white matter (NAWM) of MS patients, in the absence of any detectable blood-brain barrier breakdown, leukocyte recruitment or myelin damage [6, 7]. In vivo imaging © 2015 Peferoen et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Peferoen et al. Acta Neuropathologica Communications (2015) 3:87 studies support the notion that these so-called preactive lesions may be the first, still reversible signs of inflammatory damage that can precede actively demyelinating MS lesions by several months [8, 9]. Previously, we have documented a close association between the development of preactive MS lesions and the presence of stressed oligodendrocytes that produce large amounts of the small heat-shock protein (HSP) alpha B-crystallin (also known as HSPB5) [10]. At later stages of lesion development, high levels of HSPB5 also emerge in astrocytes [11–13]. Elevated expression of HSPB5 by oligodendrocytes during MS may have particular relevance since HSPB5 activates a regulatory innate response by microglia via Toll-like receptor (TLR) 2 and CD14, the signs of which can already be found in preactive lesions [10, 14]. In the presence of IFN-γ as an additional co-stimulus, however, HSPB5 triggers a classical state of activation in microglia and macrophages, which is characteristic of the more advanced stages of actively demyelinating lesions [15]. HSPB5 thus offers a molecular link between stressed oligodendrocytes and the development of destructive inflammation. Since other small HSP such as HSPB1 and HSPB8 have previously been reported to share TLR agonist activity with HSPB5 [16–18], the present study addressed the question whether small HSPs other than HSPB5 display similar expression profiles during lesional development in MS. The group of small HSPs consists of eleven members, HSPB1-HSPB10 and the recently described HSPB11 [19, 20]. However, whether HSPB11 really belongs to the family is still under debate [21]. The small HSPs share many structural and functional similarities, yet they differ in tissue distribution and expression patterns. HSPB1, HSPB5, HSPB6, HSPB8 and HSPB11 have been described to be present in the central nervous system either under normal condition or after stress induction [22–25]. Since not all small HSPs show the same response to particular types of stress [13, 23, 24, 26], differentiating their expression profiles may shed light on the molecular triggers that either drive or accompany the development of MS lesions. In this study, we therefore evaluated by quantitative polymerase chain reaction (qPCR) and immunohistochemical staining the expression at different stages of lesion development during MS of HSPB1, HSPB6, HSPB8 and H (...truncated)