Desacyl‐ghrelin and synthetic GH‐secretagogues modulate the production of inflammatory cytokines in mouse microglia cells stimulated by β‐amyloid fibrils

Abstract

Data from Alzheimer's disease (AD) patients and AD animal models demonstrate the accumulation of inflammatory microglia at sites of insoluble fibrillar beta-amyloid protein (fAbeta) deposition. It is known that fAbeta binds to CD36, a type B scavenger receptor also involved in internalization of oxidized low-density lipoprotein (LDL), and initiate a signaling cascade that regulates microglial recruitment, activation, and secretion of inflammatory mediators leading to neuronal dysfunction and death. The recent demonstration of a binding site for the growth hormone secretagogues (GHS) on CD36 prompted us to ascertain whether ghrelin and synthetic GHS could modulate the synthesis of inflammatory cytokines in fAbeta-activated microglia cells. We demonstrate that N9 microglia cells express the CD36 and are a suitable model to study the activation of inflammatory cytokines synthesis. In fact, in N9 cells exposed to fAbeta(25-35) for 24 hr, the expression of interleukin (IL)-1beta and IL-6 mRNA significantly increased. Interestingly, 10(-7) M desacyl-ghrelin, hexarelin, and EP80317 in the nanomolar range effectively counteracted fAbeta(25-35) stimulation of IL-6 mRNA levels, whereas ghrelin was ineffective. Similarly, the effects of fAbeta(25-35) on IL-1beta mRNA levels were attenuated by desacyl-ghrelin, hexarelin, and EP80317, but not ghrelin. Because we have observed that the specific GHS receptor GHS-R1a is not expressed in N9 cells, the actions of GHS should be mediated by different receptors. Reportedly, hexarelin and EP80317 are capable of binding the CD36 in mouse macrophages and reducing atherosclerotic plaque deposition in mice. We conclude that desacyl-ghrelin, hexarelin, and EP80317 might interfere with fAbeta activation of CD36 in microglia cells.

Identification of activated protein C as a ghrelin endopeptidase in bovine plasma

“…7A), consistent with previous reports that desacyl ghrelin does not activate the ghrelin receptor (Bednarek et al 2000, Johansson et al 2008. In contrast, desacyl ghrelin has been reported to have synergistic or antagonistic effects on ghrelin-dependent physiological events (Filigheddu et al 2007, Bulgarelli et al 2009). Desacyl ghrelin fragments protect pancreatic b-cells from oxidative stress to prevent diabetes in streptozotocin-treated rats (Granata et al 2012).…”

“…6D) and found that digested forms of ghrelin exert cellular functions in a ghrelin-receptor-dependent fashion. Importantly, these results indicate that ghrelin might have diverse health-related effects under the influence of thrombotic/thrombolytic system, including antiinflammatory (Li et al 2004, Chorny et al 2008, Waseem et al 2008, Bulgarelli et al 2009) and cardiovascular effects (Baldanzi et al 2002, Rossi et al 2007, in addition to its previously reported roles in GH release and appetite control (Wren et al 2001, Asakawa et al 2005, Drucker 2007, Sun et al 2008. Synthetic human o-ghrelin(15) can also be cleaved into smaller peptide fragments, such as o-ghrelin (14) or o-ghrelin(13) (Fig.…”

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

“…Of note, the actions of ghrelin in neuroprotection seem to be specifically mediated by the inhibition of proapoptotic molecules associated with mitochondrial pathways and by activating endogenous protective molecules (Miao et al 2007). Interestingly, ghrelin acts by inhibiting apoptotic pathways regardless of its acylation (Chung et al 2008); however, while AG acts through GHSR1a, UAG would bind to the CD36 scavenger receptor to exert these actions (Bulgarelli et al 2009). …”

Des-acyl ghrelin attenuates pilocarpine-induced limbic seizures via the ghrelin receptor and not the orexin pathway

“…Both ghrelin and DAG share an identical amino acid sequence, with the only difference that DAG lacks an O-n-octanoylation at serine 3 (Chen et al, 2009). This was believed to render DAG unable to bind with the growth hormone secretagogue receptor (now preferably denoted as ghrelin receptor (IUPHAR/BPS, 2015), and numerous studies have been performed to try to elucidate the receptor on which DAG exerts its function (Bulgarelli et al, 2009;Delhanty et al, 2012Delhanty et al, , 2013Pei et al, 2014).…”