Trueblood KE, Mohr S, Dubyak GR. Purinergic regulation of high-glucose-induced caspase-1 activation in the rat retinal Müller cell line rMC-1. Am J Physiol Cell Physiol 301: C1213-C1223, 2011. First published August 10, 2011; doi:10.1152/ajpcell.00265.2011.-Chronic activation of proinflammatory caspase-1 in the retinas of diabetic animals and patients in vivo and retinal Müller cells in vitro is well documented. In this study we characterized how elevated glucose and extracellular purines contribute to the activation of caspase-1 in a cultured rat Müller cell (rMC-1) model. The ability of high glucose (25 mM, 24 h) to activate caspase-1 was attenuated by either apyrase, which metabolizes extracellular ATP to AMP, or adenosine deaminase (ADA), which metabolizes extracellular adenosine to inosine. This suggested that autocrine stimulation of ATPsensing P2 receptors and adenosine-sensing P1 receptors may in part mediate the response to high glucose. Exogenous ATP, 5=-N-ethylcarboxamido-adenosine (NECA), a nonselective P1 receptor agonist, or forskolin (FSK) increased caspase-1 activity in rMC-1 cells cultured in control glucose (5 mM) medium. Accumulation of active caspase-1 was also increased by dipyridamole, which suppresses adenosine reuptake. High-glucose stimulation of caspase-1 was attenuated by suramin, a nonselective P2 antagonist, or A2 adenosine receptor antagonists, but not by antagonism of P2X7 ATP-gated ion channel receptors. Although high glucose increased P2X7 mRNA, neither P2X7 protein nor function was detected in rMC-1 cells. The increased caspase-1 activity stimulated by high glucose, FSK, NECA, or ATP was correlated with increased gene expression of caspase-1 and thioredoxin-interacting-protein (TXNIP). These findings support a novel role for autocrine P1 and P2 purinergic receptors coupled to cAMP signaling cascades and transcriptional induction of caspase-1 in mediating the high-glucose-induced activation of caspase-1 and secretion of IL-1␤ in a cell culture model of nonhematopoietic retinal Müller cells. sterile inflammation; hyperglycemia; inflammasome; purinergic signaling DIABETIC RETINOPATHY, a chronic, sterile inflammatory condition, is characterized by increased levels of active caspase-1 and interleukin-1-␤ (IL-1␤), which are strongly implicated in retinal degeneration (11,15,22,31,44). One source of active caspase-1 and IL-1␤ are retinal Müller cells which, as the principal glia of the retina, provide vital structural and metabolic support to retinal neurons (5, 53, 54). As such, it has been postulated that inflammatory activation, characterized by increased caspase-1/IL-1␤ signaling and mitochondrial stress, of Müller cells under hyperglycemic conditions contributes to the development and progression of the disease (31, 44). We and others have previously reported that inhibition of caspase-1/ interleukin-1␤ signaling prevents degeneration of retinal capillaries in diabetes (11,15,22,31,44). Our more recent studies have demonstrated that a vicious cycle of autocrine activation of caspa...

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