Renal ischemia-reperfusion injury (IRI) is a major risk factor for delayed graft function in renal transplantation. Compelling evidence exists that the stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against IRI. However, the role of myeloid HO-1 during IRI remains poorly characterized. Mice with myeloid-restricted deletion of HO-1 (HO-1M-KO), littermate (LT), and wild-type (WT) mice were subjected to renal IRI or sham procedures and sacrificed after 24 hours or 7 days. In comparison to LT, HO-1M-KO exhibited significant renal histological damage, pro-inflammatory responses and oxidative stress 24 hours after reperfusion. HO-1M-KO mice also displayed impaired tubular repair and increased renal fibrosis 7 days after IRI. In WT mice, HO-1 induction with hemin specifically upregulated HO-1 within the CD11b+ F4/80lo subset of the renal myeloid cells. Prior administration of hemin to renal IRI was associated with significant increase of the renal HO-1+ CD11b+ F4/80lo myeloid cells in comparison to control mice. In contrast, this hemin-mediated protection was abolished in HO-1M-KO mice. In conclusion, myeloid HO-1 appears as a critical protective pathway against renal IRI and could be an interesting therapeutic target in renal transplantation.

The outbreak of coronavirus disease 2019 (COVID-19) requires urgent need for effective treatment. Severe COVID-19 is characterized by a cytokine storm syndrome with subsequent multiple organ failure (MOF) and acute respiratory distress syndrome (ARDS), which may lead to intensive care unit and increased risk of death. While awaiting a vaccine, targeting COVID-19-induced cytokine storm syndrome appears currently as the efficient strategy to reduce the mortality of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The stress-responsive enzyme, heme oxygenase-1 (HO-1) is largely known to protect against inflammatory response in animal models. HO-1 is induced by hemin, a well-tolerated molecule, used for decades in the treatment of acute intermittent porphyria. Experimental studies showed that hemin-induced HO-1 mitigates cytokine storm and lung injury in mouse models of sepsis and renal ischemia-reperfusion injury. Furthermore, HO-1 may also control numerous viral infections by inhibiting virus replication. In this context, we suggest the hypothesis that HO-1 cytoprotective pathway might be a promising target to control SARS-CoV-2 infection and mitigate COVID-19-induced cytokine storm and subsequent ARDS.

Cellular necrosis has long been regarded as an incidental and uncontrolled form of cell death. However, a regulated form of cell death termed necroptosis has been identified recently. Necroptosis can be induced by extracellular cytokines, pathogens and several pharmacological compounds, which share the property of triggering the formation of a RIPK3-containing molecular complex supporting cell death. Of interest, most ligands known to induce necroptosis (including notably TNF and FASL) can also promote apoptosis, and the mechanisms regulating the decision of cells to commit to one form of cell death or the other are still poorly defined. We demonstrate herein that intracellular nicotinamide adenine dinucleotide (NAD + ) has an important role in supporting cell progression to necroptosis. Using a panel of pharmacological and genetic approaches, we show that intracellular NAD + promotes necroptosis of the L929 cell line in response to TNF. Use of a pan-sirtuin inhibitor and shRNA-mediated protein knockdown led us to uncover a role for the NAD + -dependent family of sirtuins, and in particular for SIRT2 and SIRT5, in the regulation of the necroptotic cell death program. Thus, and in contrast to a generally held view, intracellular NAD + does not represent a universal pro-survival factor, but rather acts as a key metabolite regulating the choice of cell demise in response to both intrinsic and extrinsic factors. + as a substrate in a number of regulatory processes has shed a new light on its role in cell physiology. Indeed, NAD + represents a substrate for a wide range of enzymes including cADP-ribose synthases, poly (ADP-ribose) polymerases (PARPs) and the sirtuin family of NAD + -dependent deacylases (SIRTs). In marked contrast to its role in energy metabolism, the involvement of NAD + in these enzymatic reactions is based on its ability to function as a donor of ADP-ribose, a reaction that, if sustained, can lead to the depletion of the intracellular NAD + pool. 1-5The pro-survival role of NAD + has been particularly well described in cells exposed to genotoxic/oxidative stress. In response to DNA damage, PARP1, the founding and most abundant member of the PARP family, binds to DNA strand breaks and initiates a repair response by catalyzing the posttranslational modification of several nuclear proteins, including itself. This protective response is characterized by the transfer of successive units of the ADP-ribose moiety (up to 200 units) from NAD + to other proteins, compromising therefore both energy production (slowing the rate of glycolysis, electron transport and ATP formation) and activity of other NAD + -dependent enzymes through NAD + depletion. 6,7 Moreover, PARP1-synthesized PAR polymers can be degraded into free oligomers, known to translocate to the mitochondria where they can trigger the release of AIF from mitochondria to the nucleus. [8][9][10][11] The precise molecular steps linking PARP1 activation to this form of stress-induced cell death, termed parthanatos, have not been fully elucidated, and...

No abstract