Inhibition of mitochondrial oxidative metabolism attenuates EMCV replication and protects β-cells from virally mediated lysis

Abstract

Viral infection is one environmental factor that may contribute to the initiation of pancreatic β-cell destruction during the development of autoimmune diabetes. Picornaviruses, such as encephalomyocarditis virus (EMCV), induce a pro-inflammatory response in islets leading to local production of cytokines, such as IL-1, by resident islet leukocytes. Furthermore, IL-1 is known to stimulate β-cell expression of iNOS and production of the free radical nitric oxide. The purpose of this study was to determine whether nitric oxide contributes to the β-cells response to viral infection. We show that nitric oxide protects β-cells against virally mediated lysis by limiting EMCV replication. This protection requires low micromolar, or iNOS-derived, levels of nitric oxide. At these concentrations nitric oxide inhibits the TCA enzyme aconitase and complex IV of the electron transport chain. Like nitric oxide, pharmacological inhibition of mitochondrial oxidative metabolism attenuates EMCV-mediated β-cell lysis by inhibiting viral replication. These findings provide novel evidence that cytokine signaling in β-cells functions to limit viral replication and subsequent β-cell lysis by attenuating mitochondrial oxidative metabolism in a nitric oxide-dependent manner.

Single-cell RNA sequencing of mouse islets exposed to proinflammatory cytokines

“…Generally, cytokines and nitric oxide are viewed as damaging to β-cells based on observations that exogenous IL-1β treatment impairs oxidative phosphorylation and insulin secretion and eventually causes β-cell death with prolonged exposure in a nitric oxide–dependent manner ( Mandrup-Poulsen et al, 1985 ; Bendtzen et al, 1986 ; Southern et al, 1990 ; Welsh et al, 1991 ; Corbett & McDaniel, 1992 , 1995 ; Corbett et al, 1992a, 1993 ; Cunningham & Green, 1994 ; Mandrup-Poulsen, 1996 ). However, our recent studies suggest that the ability of nitric oxide to inhibit mitochondrial oxidation and ATP generation protects β-cells from apoptosis ( Oleson et al, 2016 ) and viral infection ( Stafford et al, 2020 ). Our observations here that IL-1β induces antiviral genes ( Fig 3 ) and fails to induce apoptotic mediators ( Fig S4 ) dovetail with these recent findings and further support the idea that the primary functions of IL-1β and nitric oxide are to protect β-cells from damage.…”

“…Together with the observation that cytokine-induced nitric oxide promotes heat shock protein expression in rat islets ( Helqvist et al, 1991 ), our results suggest that the heat shock response may provide an internal “off switch” to prevent cytokine-mediated islet damage after protective signaling has been initiated. In other words, nitric oxide may not only protect β-cells through inhibition of mitochondrial oxidation ( Oleson et al, 2016 ; Stafford et al, 2020 ), but may also provide a means to shut down prolonged cytokine signaling, which is known to be damaging.…”

“…Nitric oxide, produced in β-cells after the expression of inducible nitric oxide synthase (iNOS) in response to IL-1β exposure, mediates these damaging effects ( Southern et al, 1990; Corbett et al, 1991 , 1992a , 1993 ; Welsh et al, 1991 ; Corbett & McDaniel, 1992 ). However, whereas IL-1β and nitric oxide are primarily viewed as damaging to the islet, we have recently shown that nitric oxide protects β-cells against DNA damage–induced apoptosis and against viral infection ( Oleson et al, 2016 ; Stafford et al, 2020 ).…”

Regulation of ATR-dependent DNA damage response by nitric oxide

“…While additional studies are required to more fully appreciate the roles of nitric oxide production in regulating DDR signaling in β-cells, our studies are beginning to shed light on the physiological roles for cytokine signaling, iNOS expression and the production of nitric oxide by β-cells. On such role being the inhibition of picornavirus replication in a pancreatic β-cell selective manner (67,68). Cell culture and islet isolation.…”

Inhibition of oxidative metabolism by nitric oxide restricts EMCV replication selectively in pancreatic beta-cells

“…In reevaluating these contrasting responses, we reasoned that cytokine signaling in β-cells could play a physiologically protective role in promoting β-cell survival, and in support of this hypothesis, we have recently shown that nitric oxide attenuates EMCV replication in insulinoma MIN6 cells and mouse islets by inhibiting mitochondrial oxidative metabolism ( 25 ). Inhibitors of the electron transport chain and mitochondrial uncouplers attenuate EMCV replication and EMCV-mediated MIN6 cell lysis in a manner like nitric oxide.…”