Are heat shock proteins involved in autoimmunity?

Interplay between the Chaperone System and Gut Microbiota Dysbiosis in Systemic Lupus Erythematosus Pathogenesis: Is Molecular Mimicry the Missing Link between Those Two Factors?

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease characterized by self-immune tolerance breakdown and the production of autoantibodies, causing the deposition of immune complexes and triggering inflammation and immune-mediated damage. SLE pathogenesis involves genetic predisposition and a combination of environmental factors. Clinical manifestations are variable, making an early diagnosis challenging. Heat shock proteins (Hsps), belonging to the chaperone system, interact with the immune system, acting as pro-inflammatory factors, autoantigens, as well as immune tolerance promoters. Increased levels of some Hsps and the production of autoantibodies against them are correlated with SLE onset and progression. The production of these autoantibodies has been attributed to molecular mimicry, occurring upon viral and bacterial infections, since they are evolutionary highly conserved. Gut microbiota dysbiosis has been associated with the occurrence and severity of SLE. Numerous findings suggest that proteins and metabolites of commensal bacteria can mimic autoantigens, inducing autoimmunity, because of molecular mimicry. Here, we propose that shared epitopes between human Hsps and those of gut commensal bacteria cause the production of anti-Hsp autoantibodies that cross-react with human molecules, contributing to SLE pathogenesis. Thus, the involvement of the chaperone system, gut microbiota dysbiosis, and molecular mimicry in SLE ought to be coordinately studied.

Heat-shock proteins as powerful weapons in vaccine development

Heat-shock proteins (HSPs) have been known as multifunctional proteins. They facilitate the folding and unfolding of proteins, participate in vesicular transport processes, prevent protein aggregation in the densely packed cytosol and are involved in signaling processes. HSPs have been involved in different fields, including autoimmunity, immunity to infections and tumor immunology. Although there are many different kinds of HSPs, only some HSPs, including HSP70 and Gp96, have immunological properties. HSP molecules have been applied into DNA- or protein (peptide)-based vaccines as antigens, chaperones or adjuvants. HSP-based vaccines have been shown to immunize against cancer and infectious diseases in both prophylactic and therapeutic protocols. The immunogenicity of HSPs results from two different properties: a peptide-dependent capacity to chaperone and elicit adaptive cytotoxic T-lymphocyte responses against antigenic peptides and a peptide-independent immunomodulatory capacity. Furthermore, HSPs could be immunoregulatory agents with potent and widely applicable therapeutic uses. Accordingly, certain HSPs, such as HSP70 and Gp96, are highly effective carrier molecules for cross-presentation. Their ability in eliciting immune responses against different pathogens (parasite and virus) and their role in cancer immunity will be discussed in this review.

Downregulation of a rheumatoid arthritis-related antigen (RA-A47) by ra-a47 antisense oligonucleotides induces inflammatory factors in chondrocytes

Previously we have shown that the expression of RA-A47 (rheumatoid arthritis-related antigen) which is identical to HSP47, a collagen-binding chaperon, is downregulated in chondrocytes by tumor necrosis factor alpha (TNFalpha). RA-A47 was also found on the surface of chondrocytes where it is recognized as an antigen in the serum of rheumatoid arthritis (RA) patients. Its translocation to the cell surface from endoplasmic reticulum membrane where it is normally located was also enhanced by TNFalpha. To understand the significance of RA-A47 downregulation in chondrocytes independent from other effects of TNFalpha, we used an antisense oligonucleotide approach and investigated the effect of this treatment on the expression of molecules related to matrix degradation and production of growth factors for chondrocytic, endothelial, and synovial cells. Here we show that treatment of rabbit chondrocyes and human chondrosarcoma cells HCS-2/8 by ra-a47 antisense S-oligonucleotides significantly reduced the expression of ra-a47 both at mRNA and protein level. Interestingly, this TNFalpha-independent RA-A47 downregulation was associated with a strong induction of matrix metalloproteinase (MMP)-9 mRNA and inducible NO synthase (iNOS) mRNA. The induction of active-type MMP-9 was further detected by gelatin zymography. Under the same conditions, the release of basic fibroblast growth factor (bFGF) and connective tissue growth factor (CTGF) from HCS-2/8 cells into the conditioned medium (CM) was strongly enhanced. These effects were not a result of TNFalpha upregulation, since the ra-a47 antisense oligonucleotide treatment did not enhance TNFalpha synthesis. These observations indicate that downregulation of RA-A47 induces TNFalpha-independent cartilage-degrading pathways involving iNOS and MMP-9. Furthermore, the stimulation of bFGF and CTGF release from chondrocytes may stimulate the proliferation of adjacent endothelial and/or synovial cells.

Stress proteins: nomenclature, division and functions

The heat shock response, characterized by increased expression of heat shock proteins (Hsps) is induced by exposure of cells and tissues to extreme conditions that cause acute or chronic stress. Hsps function as molecular chaperones in regulating cellular homeostasis and promoting survival. If the stress is too severe, a signal that leads to programmed cell death, apoptosis, is activated, thereby providing a finely tuned balance between survival and death. In addition to extracellular stimuli, several nonstressfull conditions induce Hsps during normal cellular growth and development. The enhanced heat shock gene expression in response to various stimuli is regulated by heat shock transcription factors.

The role of hsp90 in SLE

The heat shock proteins are a group of evolutionarily conserved proteins with important physiological functions, whose synthesis is enhanced by elevated temperature or other stresses. A role for one or more of these proteins in human autoimmune disease has been extensively discussed. This review considers the evidence of a role for hsp90 in systemic lupus erythematosus (SLE) where overexpression of this protein, its surface localization and auto-antibodies to it have been observed in both human patients and in the MRL/lpr mouse model of SLE.