Activation of Heat Shock Factor 1 Attenuates Murine Intestinal Inflammation via Enhanced Treg Function

Abstract

Inflammatory Bowel Disease (IBD) is a chronic inflammatory condition thought to reflect a failure of the enteral immune system to adequately regulate itself, resulting in unrestrained inflammation. Regulatory T cells (Tregs) mediate suppression of this overactive immune response; therefore, better understanding of their role in the pathogenesis of IBD will undoubtedly inform the development of novel therapies. Previous data demonstrates that inhibition of heat shock protein 90 (HSP90) activity enhances Treg function via a mechanism involving disruption of a complex containing HSP90 and heat-shock factor 1 (HSF1). Genetic deficiency in HSF1 has been shown previously to result in more severe chemically-induced colitis, yet efforts to enhance HSF1 activation in mouse models of IBD have not been attempted to date. Heat-shock proteins are up-regulated in response to cellular stress including inflammation to prevent protein misfolding and aggregation as well as to act as molecular chaperone proteins to drive de novo transcription. HSF1 has been shown previously to translocate to the nucleus and drive expression of a number of anti-inflammatory genes such as IL-10 and HSP70. We hypothesized, therefore, that enhanced HSF1 function might enhance Treg function and thereby attenuate murine colitis. Heat shock (42oC, 30 min) of naïve CD4+ T cells resulted in a significant increase in Treg induction upon anti-CD3 activation when coupled with TGFb. Conversion from naïve cell to Treg coincided with shuttling of HSF1 from the cytoplasm into the nucleus within 1 hr of stimulation with anti-CD3 as well as a significant increase in nuclear expression of HSF1 from bona fide Tregs relative to naïve CD4+ CD25neg T cells. In contrast, genetic deletion of HSF1 resulted in a decrease in intestinal Foxp3+ Treg frequency along with impaired Treg suppressive function in vitro. This phenomenon is characteristic of human IBD. Administration of Celastrol, an HSF1 activator, enhanced Treg suppressive function and drove translocation of HSF1 from the cytoplasm into the nucleus in WT cells relative to vehicle controls. HSF1 translocation in turn resulted in upregulation of IL-10 mRNA transcripts in isolated Tregs in vitro. Activation of HSF1 with Celastrol attenuated established inflammation in the T-cell driven CD45RBHigh colitis model. Two week continuous treatment with an osmotic pump attenuated histological evidence of inflammation and increased the frequency of Foxp3+ IL-10 producing Tregs in the colonic lamina propria. Targeting HSF1 for therapeutic benefit represents an exciting strategy, as HSF1 is preferentially upregulated at sites of specific inflammation. Furthermore, as we increase our understanding of the anti-inflammatory mechanisms of HSF1 activation in murine models of IBD, this data will provide proof of principle for the expansion of current clinical trials using HSF1 activators for cancer chemotherapy to include indications in IBD. Funding from K08DK080189 (EDZ) & CCFA-2652 (CBC) and UL1 RR025780 (EDZ & CBC).