Regional differences in colonic mucosa-associated microbiota determine the physiological expression of host heat shock proteins

Abstract

Cytoprotective heat shock proteins (Hsps) are critical for intestinal homeostasis and are known to be decreased in inflammatory bowel diseases. Signals responsible for maintenance of Hsp expression are incompletely understood. In this study, we find that Hsp25/27 and Hsp70 protein expressions are differentially regulated along the longitudinal length of the large intestine, being highest in the proximal colon and decreasing to the distal colon. This longitudinal gradient was similar in both conventionally colonized mouse colon as well as biopsies of human proximal and distal colon but was abolished in the colon of germ-free mice, suggesting a role of intestinal microbiota in the Hsp regional expression. Correspondingly, analysis of 16S ribosomal RNA genes of bacteria from each colonic segment indicated increased bacterial richness and diversity in the proximal colon. The mechanism of regulation is transcriptional, as Hsp70 mRNA followed a similar pattern to Hsp70 protein expression. Lysates of mucosa-associated bacteria from the proximal colon stimulated greater Hsp25 and Hsp70 mRNA transcription and subsequent protein expression in intestinal epithelial cells than did lysates from distal colon. In addition, transrectal administration of cecal contents stimulated Hsp25 and Hsp70 expression in the distal colon. Thus host-microbial interactions resulting in differential Hsp expression may have significant implications for the maintenance of intestinal homeostasis and possibly for development of inflammatory diseases of the bowel.

Expression of heat shock proteins 27 and 72 correlates with specific commensal microbes in different regions of porcine gastrointestinal tract

“…Experiments in rodents and humans have shown that expression of intestinal HSP25/27 and HSP72 is dependent on the presence of gut microbiota (19,26). In a striking difference to our results, those studies found that the proximal colonic mucosa exerted the strongest HSP25/27 and HSP72 expression, due to the highly diversified and dense bacteria population.…”

“…Indeed, microbiota is one of the major determinants of HSP expression in IECs, as has been clearly demonstrated in antibiotic-treated mice, in which HSP25 and HSP72 are significantly reduced in the colonic mucosa (26). Moreover, HSP expression is absent in the gut of germ-free mice (19). An unexpected finding in the present study was that the distal ileal mucosa in pigs exhibited stronger expression of both HSPs than the proximal colon.…”

“…In the healthy porcine gut, we found a pattern in expression of both HSP27 and HSP72 along the villus/crypt axis, with the highest expression at the surface epithelium, lowest expression in crypt cells, and limited expression in the lamina propria. This suggests that physiological expression of HSPs is most likely dependent on dietary components, microbes, and the metabolites to which the mucosa surface is exposed, as seen in human and mouse colonic mucosa (19,26). Indeed, microbiota is one of the major determinants of HSP expression in IECs, as has been clearly demonstrated in antibiotic-treated mice, in which HSP25 and HSP72 are significantly reduced in the colonic mucosa (26).…”

“…Such colonization is known to be essential for the maintenance of host immune homeostasis (22). Indeed, the intestinal mucosal immune system of germ-free mice is typically undeveloped, with hypoplastic Peyer's patches (PPs) (32), lack of regulatory T (T reg ) cells (21), and minimal expression of heat shock protein (HSP) 25 and HSP70 (19). Disruption of the balance between host immunity and microbiota can easily lead to dysbiosis (microbial imbalance), which is believed to be a crucial step in disease progression, for example of diarrhea or inflammatory bowel disease (IBD) in humans (11,41) and swine dysentery in pigs (43).…”

Heat shock proteins are no DAMPs, rather 'DAMPERs'

“…Based on the current experimental data, it seems that HSPs are key elements in the type of immune system responsiveness or reactivity that is induced by the following three typical conditions: one, sterile tissue damage, when tissue-derived HSPs in combination with DAMPs activate tissue repair and regulation; two, damage caused by infectious pathogens, when HSPs in the presence of DAMPs and pathogen-derived PAMPs lead to a full proinflammatory response with elimination of infection and regulation; and three, homeostatic interactions with commensal symbionts of the gut microbiota, when a combination of PAMPs and HSPs leads to the regulation and maintenance of symbiosis [22][23][24] . Given the ubiquitous presence and stressinducible nature of HSPs in both tissue cells and microbial invaders or symbionts, therapeutic targeting of HSPs offers an attractive possibility for the fine-tuning of such immune responses and the dampening of inflammation through the induction or activation of regulatory T cells.…”