Major role of HSP70 as a paracrine inducer of cytokine production in human oxidized LDL treated macrophages

Abstract

Lipid accumulation and inflammation are key hallmarks of the atherosclerotic plaque and macrophage uptake of oxidized low-density lipoprotein (oxLDL) is believed to drive these processes. Initial experiments show that supernatants from oxLDL treated macrophages could induce IL-1β production in naïve macrophages. To search for potential paracrine mediators that could mediate this effect a DNA microarray scan of oxLDL treated human macrophages was performed. This analysis revealed that oxLDL induced activation of heat shock protein (HSP) expression. HSPs have been implicated in the development of atherosclerosis, but the exact mechanisms for this is unclear. Extracellular heat shock protein 70 (HSP70) has been shown to elicit a pro-inflammatory cytokine response in monocytes and could therefore be a potential paracrine pro-inflammatory mediator. After 24 h of oxLDL treatment there was a significant increase of HSP70 concentrations in supernatants from oxLDL treated macrophages (oxLDLsup) compared to untreated controls (P < 0.05). OxLDLsup could induce both interleukin (IL)-1β and IL-12 secretion in naïve macrophages. We also demonstrate that the effect of oxLDLsup on cytokine production and release could be blocked by inhibition of HSP70 transcription or secretion or by the use of HSP70 neutralizing antibodies. This suggests that extracellular HSP70 can mediate pro-inflammatory changes in macrophages in response to oxLDL.

Extracellular Release of the Atheroprotective Heat Shock Protein 27 Is Mediated by Estrogen and Competitively Inhibits acLDL Binding to Scavenger Receptor-A

“…For example, HSP70 can bind toll-like receptors 2 and 4 (TLR-2 and -4) and thereby induce NFB activation, IL-6 production, as well as the secretion of IL-1␤ and IL-12-both proinflammatory cytokines. 22,33 Other reports show that SR-A is capable of binding Gp96, an endoplasmic reticulum-bound HSP on antigen presenting cells. 34 However, we now show that HSP27 may have effects opposite to those observed for other extracellular HSPs.…”

Diet-induced elevation of circulating HSP70 may trigger cell adhesion and promote the development of atherosclerosis in rats

“…Functional studies have also reported that extracellular HSP70 could stimulate the production of anti-inflammatory cytokine IL-10 in responsive T cells (Wendling et al 2000) and attenuate the intimal thickening in mice exposed to cigarette smoke (Matsumoto et al 2008). In contrast, some conflicting reports showed the adverse effects of circulating HSP70 as a paracrine inducer of proinflammatory cytokines, especially IL-6, which exacerbate the inflammatory process in the development of atherosclerosis plaques (Asea et al 2000;Gonzalez-Ramos et al 2013;Svensson et al 2006). HSP70 serum concentration was also shown to increase in patients with peripheral atherosclerosis according to some epidemiological investigations (Wright et al 2000).…”

Atherogenesis and the humoral immune response to modified lipoproteins

“…The immune system also appears to recognize other by-products of macrophage activation, such as heat shock proteins (Hsp) [16]. Hsp are also immunogenic [17], and are also able to activate macrophages through interactions with Toll-like receptors [18] and lipid rafts [19,20]. Therefore, a variety of circuits are activated by modified lipoproteins and mLDL-IC, setting the conditions for a chronic inflammatory reaction in the vessel walls.…”