Heat Shock Protein 27 Immune Complex Altered Signaling and Transport (ICAST): Novel Mechanisms of Attenuating Inflammation

Abstract

Blood levels of heat shock protein (HSP27) and natural IgG auto-antibodies to HSP27 (AAbs) are higher in healthy controls compared to cardiovascular disease patients. Vaccination of mice with recombinant HSP25 (rHSP25, murine ortholog of human rHSP27) increased AAb levels, attenuated atherogenesis and reduced plaque inflammation and cholesterol content. We sought to determine if the HSP27 immune complex (IC) altered MΦ inflammation signaling (Toll Like Receptor 4; TLR4), and scavenger receptors involved in cholesterol uptake (SR-AI, CD-36). Combining a validated polyclonal IgG anti-HSP27 antibody (PAb) with rHSP27 enhanced binding to THP-1 MΦ cell membranes and activation of NF-κB signaling via TLR4, competing away LPS and effecting an anti-inflammatory cytokine profile. Similarly, adding the PAb with rHSP27 enhanced binding to SR-AI and CD-36, as well as lowered oxLDL binding in HEK293 cells separately transfected with SR-AI and CD-36, or THP-1 MΦ. Finally, the PAb enhanced the uptake and internalization of rHSP27 in THP-1 MΦ. Thus, the HSP27 IC potentiates HSP27 cell membrane signaling with receptors involved in modulating inflammation and cholesterol uptake, as well as HSP27 internalization. Going forward, we will explore HSP27 Immune Complex Altered Signaling and Transport (ICAST) as a new anti-inflammatory therapeutic strategy in vivo.

Sex differences in COVID-19 mortality: opportunity to develop HSP27 (HSPB1) immunotherapy to treat hyper-inflammation?

“…What we also uncovered is a complex relationship between HSP27 and estrogens, as HSP27 acts as a repressor of estrogen-mediated transcription in vitro, yet its expression and extracellular release are also partially regulated by estrogens (e.g., there is an estrogen response element found in the HSP27 promoter) (Miller et al 2005;Rayner et al 2009). As well, we recently noted that natural IgG auto-antibodies to HSP27 (AAbs) are detectable in human blood (Chen et al 2020b) and demonstrated how HSP27 immune complexes (ICs) form, dock at the cell membrane where they engage with Toll-like receptor 4 (TLR4), and compete with LPS to reduce inflammatory signaling (Shi et al 2020). Interestingly, HSP27 activates the NF-κB pathway-but only modestly-resulting in the expression of both pro-and anti-inflammatory cytokines and proteins (Salari et al 2013).…”

“…Interestingly, HSP27 activates the NF-κB pathway-but only modestly-resulting in the expression of both pro-and anti-inflammatory cytokines and proteins (Salari et al 2013). Boosting HSP27 antibodies via vaccination reduces atherosclerosis and promotes the antiinflammatory effects of the HSP27 immune complex (Shi et al 2020). It is the combination of the protein and its antibody that produces the therapeutic benefit-a concept that we refer to as HSP27 Immune Complex Altered Signaling and Transport (or ICAST; transport refers to cellular internalization of HSP27).…”

“…Treatment of macrophages with exogenous recombinant HSP27 reduces the uptake of modified low-density lipoprotein (LDL), lowers IL-1β levels, and increases levels of an anti-inflammatory cytokine, IL-10 (Miller-Graziano et al 2008;Rayner et al 2008). Additionally, extracellular recombinant HSP27 inhibits modified LDL uptake by competing for scavenger receptors, SR-A and CD36 (Shi et al 2020). Scavenger receptors bind modified LDL and intiate both signals 1 and 2 for complete NLRP3 inflammasome activation.…”

The Heat Shock Protein 27 Immune Complex Enhances Exosomal Cholesterol Efflux

“…To study the in vitro role of exosomal HSP27 we will incorporate new information showing that anti-HSP27 IgG antibodies levels are more abundant in healthy subjects vs. CVD patients. To this end, we have generated and validated a polyclonal anti-HSP27 IgG antibody (PAb) that combines with HSP27 to form an immune complex (IC) that facilitates the biological effects of HSP27 (referred to as Immune Complex Altered Signaling and Transport (ICAST)) [18,26].…”

Correlation between Serum Heat Shock Protein 27 and Interleukin- 17 Levels and Prognosis in Patients with Acute Myocardial Infarction

“…However, whether it plays a protective or destructive role in the in ammatory process is still controversial [7]. HSP27 and IL-17 can act through NF-κ B pathway [8][9][10]. But it is not clear whether there is a synergistic or antagonistic effect among them.…”