AICAR suppresses TNF-α-induced complement factor B in RPE cells

Abstract

Age related macular degeneration is the leading cause of blindness in the developed world. Although its precise cause remains elusive, dysfunction of the retinal pigment epithelium (RPE) and dysregulation of complement have been implicated in its pathogenesis. The goal of this study was to evaluate the role of an AMP-dependent kinase (AMPK) activator, 5-aminoimidazole-4-carboxamide riboside (AICAR), on tumor necrosis factor alpha (TNF-α) induction of complement factor B (CFB) in RPE cells. We found that AICAR inhibited TNF-α-induced CFB expression in ARPE-19 and human primary RPE cells in a dose-dependent fashion. Treatment of cells with dipyridamole, which blocks AICAR cellular uptake abolished these effects. In contrast, the adenosine kinase inhibitor, 5-iodotubericidin, which inhibits the conversion of AICAR to the direct activator of AMPK, ZMP, did not reverse the effects on TNF-α-induced CFB expression, suggesting AMPK-independent effects. Indeed, knockout of AMPK in RPE cells using Clustered Regularly Interspaced Palindromic Repeats (CRISPR)/Cas9 did not abolish the inhibitory effects of AICAR on RPE CFB expression. Collectively, our results suggest that AICAR can suppress TNF-α-induced CFB expression in RPE cells in an AMPK-independent mechanism, and could be used as a therapeutic target in certain complement over-activation scenarios.

Acadesine suppresses TNF-α induced complement component 3 (C3), in retinal pigment epithelial (RPE) cells

“…Acadesine, can exert its effects through either extracellular or intracellular mechanisms. To examine if acadesine’s effects are mediated via an extracellular or via an intracellular mechanism we used dipyridamole (DPY) which blocks the cell membrane adenosine transporters and prevents acadesine uptake into the cells [ 37 ]. Pretreatment with 4 μM of DPY abolished the effect of acadesine on TNF-α induced C3 protein expression in both human primary and ARPE-19 cell lysates ( Fig 2 ).…”

“…This result is in agreement with previous studies in which inflammatory cytokines like TNF-α induced complement component synthesis [ 48 , 49 ]. Acadesine has anti-inflammatory properties [ 33 , 34 , 37 , 45 ], is an exercise mimetic [ 71 , 72 ] and has been used in human clinical trials as a cardioprotectant [ 73 , 74 ]. Pre-treatment of human RPE cells with the AMP analog, acadesine, downregulated TNF-α induced C3 and its cleaved products C3α and C3β.Cleavage of C3 alpha chain leads to C3a, which is an anaphylatoxin and is implicated in a variety of studies with AMD pathology.…”

“…Acadesine (5-Aminoimidazole-4-carboxamide-1-β-D-ribofuranoside) is an adenosine analog which has cytoprotective properties [32] as well as anti-inflammatory and anti-exudative properties [33][34][35][36][37]. Acadesine is taken up into cells by adenosine transporters [38] and subsequently is phosphorylated by adenosine kinase to generate ZMP, an adenosine monophosphate (AMP)-mimetic and activator of AMPK [39].…”

“…Acadesine is taken up into cells by adenosine transporters [38] and subsequently is phosphorylated by adenosine kinase to generate ZMP, an adenosine monophosphate (AMP)-mimetic and activator of AMPK [39]. Activation of AMPK has been shown to suppress inflammation, and ameliorate exudation [33][34][35][36][37][40][41][42][43][44][45][46] and has been implicated in vascular cytoprotection against complement-mediated injury [47]. Hence, we wanted to explore the potential effect of acadesine in suppressing inflammatory induction of C3 in RPE cells and explore its mechanism of action.…”

The effect of complement factor B gene variation on age-related macular degeneration in Iranian patients

“…CFB protein is produced in several parts of the eye including the choroid, RPE, and neural retina 11 . Previous studies have shown that pro-inflammatory cytokines of TNF-α and IFN-γ can up-regulate the expression of CFB in RPE cells 12, 13. A study performed by Crowley et al.…”