PurposeProgrammed Death-1 (PD-1) and its ligand, PD-L1, are regulators of immune/ inflammatory mechanisms. We explored the potential involvement of PD-1/PD-L1 pathway in the inflammatory response and tissue damage in cardiac injury models.Experimental DesignIschemic-reperfused and cryoinjured hearts were processed for flow cytometry and immunohistochemical studies for determination of cardiac PD-1 and PD-L1 in the context of assessment of the growth arrest- and DNA damage-inducible protein 153 (GADD153) which regulates both inflammation and cell death. Further, we explored the potential ability of injured cardiac cells to influence proliferation of T lymphocytes.ResultsThe isolated ischemic-reperfused hearts displayed marked increases in expression of PD-1 and PD-L1 in cardiomyocytes; however, immunofluorescent studies indicate that PD-1 and PD-L1 are not primarily co-expressed on the same cardiomyocytes. Upregulation of PD-1/PD-L1 was associated with a) marked increases in GADD153 and interleukin (IL)-17 but a mild increase in IL-10 and b) disruption of mitochondrial membrane potential (ψm) as well as apoptotic and necrotic cell death. Importantly, while isotype matching treatment did not affect the aforementioned changes, treatment with the PD-L1 blocking antibody reversed those effects in association with marked cardioprotection. Further, ischemic-reperfused cardiac cells reduced proliferation of T lymphocytes, an effect partially reversed by PD-L1 antibody. Subsequent studies using the cryoinjury model of myocardial infarction revealed significant increases in PD-1, PD-L1, GADD153 and IL-17 positive cells in association with significant apoptosis/necrosis.ConclusionsThe data suggest that upregulation of PD-1/PD-L1 pathway in cardiac injury models mediates tissue damage likely through a paracrine mechanism. Importantly, inhibition of T cell proliferation by ischemic-reperfused cardiac cells is consistent with the negative immunoregulatory role of PD-1/PD-L1 pathway, likely reflecting an endogenous cardiac mechanism to curtail the deleterious impact of infiltrating immune cells to the damaged myocardium. The balance of these countervailing effects determines the extent of cardiac injury.

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BackgroundChromium picolinate (Cr(pic)3) is advocated as adjuvant therapy for impaired glycemic control, despite concerns for DNA damage. Potential toxicity of Cr(pic)3 should be greater for the kidney that accumulates chromium. Therefore, we tested the hypothesis that Cr(pic)3 treatment of obese Zucker rats (OZR) exacerbates renal abnormalities associated with dysglycemia.MethodsMale OZR were treated with diets lacking or containing 5 and 10 mg/kg of chromium, as Cr(pic)3, for 20 weeks; lean Zucker rats (LZR) served as controls. Glycemic and renal effects of Cr(pic)3 were determined in the context of indices of oxidative stress and inflammation.ResultsThe OZR displayed increased fasting plasma glucose and insulin in association with enlarged pancreatic islets exhibiting collagen and periodic acid Schiff-positive deposits compared to LZR; Cr(pic)3 treatment did not affect these parameters. The OZR, irrespective of Cr(pic)3, excreted more albumin than LZR. Also, other indices of renal function or histopathology were not affected by Cr(pic)3 treatment. Urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG), an index of oxidative DNA damage, was greater in the OZR than LZR; dietary Cr(pic)3 treatment attenuated 8-OHdG excretion. However, immunostaining of kidney for 8-OHdG revealed similar staining pattern and intensity, despite significant renal accumulation of chromium in Cr(pic)3-treated groups. Finally, increased renal nitrotyrosine and cyclooxygenase-2 levels and urinary excretion of monocyte chemoattractant protein-1 of OZR were partially reversed by Cr(pic)3 treatment.ConclusionDietary Cr(pic)3 treatment of OZR does not beneficially influence glycemic status or increase the risk for oxidative DNA damage; rather, the treatment attenuates indices of oxidative stress and inflammation.

Abstract-The growth arrest-and DNA-damage inducible protein 153 (GADD153) regulates both apoptosis and inflammatory response. Importantly, glycogen synthase kinase-3β (GSK-3β) may provide a mechanistic link for cellular expression of GADD153, inflammatory response, and cell death. We previously showed that pressure overload exacerbates myocardial ischemia reperfusion injury associated with significant reduction in phosphorylated (inactive) GSK-3β. This raises the possibility that pressure overload, through a GSK-3β-dependent mechanism, increases GADD153 expression, thereby upregulating inflammatory cytokine production and contributing to worsening of myocardial ischemia reperfusion injury. Accordingly, Langendorff-perfused rat hearts were subjected to global ischemia reperfusion protocol in the absence or presence of the GSK-3β inhibitor, lithium chloride (1 mmol/L), with perfusion pressure set at 80 or 160 cmH 2 O; normoxic hearts served as controls. Compared with normoxia, an ischemia reperfusion insult increased expressions of proinflammatory cytokines, γH2AX, and GADD153 in association with increased cell death. In the ischemic-reperfused hearts, pressure overload did the following: (1) reduced interleukin-10 but increased interleukin-17 (cardiomyocytes), without affecting interleukin-23; (2) increased expressions of γH2AX and GADD153; (3) decreased 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) aggregates but increased JC-1 monomers (suggestive of reduced mitochondrial membrane potential, ψ m ); and (4) increased annexin V immunostaining as well as apoptotic and necrotic cell death. Treatment with lithium chloride caused a robust increase in interleukin-10, preserved ψ m , and markedly decreased all other parameters with the effect being most prominent for hearts perfused at the high pressure.In conclusion, pressure overload, via a GSK-3β-dependent mechanism, exacerbates cell death in the isolated ischemicreperfused heart involving regulation of inflammatory response, DNA injury, and GADD153 expression.