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Endothelial progenitor cells (EPCs) are reduced in number and impaired in function in diabetic patients. Whether and how Nrf2 regulates the function of diabetic EPCs remains unclear. In this study, we found that the expression of Nrf2 and its downstream genes were decreased in EPCs from both diabetic patients and db/db mice. Survival ability and angiogenic function of EPCs from diabetic patients and db/db mice also were impaired. Gain- and loss-of-function studies, respectively, showed that knockdown of Nrf2 increased apoptosis and impaired tube formation in EPCs from healthy donors and wild-type mice, while Nrf2 overexpression decreased apoptosis and rescued tube formation in EPCs from diabetic patients and db/db mice. Additionally, proangiogenic function of Nrf2-manipulated mouse EPCs was validated in db/db mice with hind limb ischemia. Mechanistic studies demonstrated that diabetes induced mitochondrial fragmentation and dysfunction of EPCs by dysregulating the abundance of proteins controlling mitochondrial dynamics; upregulating Nrf2 expression attenuated diabetes-induced mitochondrial fragmentation and dysfunction and rectified the abundance of proteins controlling mitochondrial dynamics. Further RNA-sequencing analysis demonstrated that Nrf2 specifically upregulated the transcription of isocitrate dehydrogenase 2 (IDH2), a key enzyme regulating tricarboxylic acid cycle and mitochondrial function. Overexpression of IDH2 rectified Nrf2 knockdown- or diabetes-induced mitochondrial fragmentation and EPC dysfunction. In a therapeutic approach, supplementation of an Nrf2 activator sulforaphane enhanced angiogenesis and blood perfusion recovery in db/db mice with hind limb ischemia. Collectively, these findings indicate that Nrf2 is a potential therapeutic target for improving diabetic EPC function. Thus, elevating Nrf2 expression enhances EPC resistance to diabetes-induced oxidative damage and improves therapeutic efficacy of EPCs in treating diabetic limb ischemia likely via transcriptional upregulation of IDH2 expression and improving mitochondrial function of diabetic EPCs.

BACKGROUND AND AIMS Fibroblast growth factor (FGF) 1 demonstrated protection against nonalcoholic fatty liver disease (NAFLD) in type 2 diabetic and obese mice by an uncertain mechanism. This study investigated the therapeutic activity and mechanism of a nonmitogenic FGF1 variant carrying 3 substitutions of heparin-binding sites (FGF1△HBS ) against NAFLD. APPROACH AND RESULTS FGF1△HBS administration was effective in 9-month-old diabetic mice carrying a homozygous mutation in the leptin receptor gene (db/db) with NAFLD; liver weight, lipid deposition, and inflammation declined and liver injury decreased. FGF1△HBS reduced oxidative stress by stimulating nuclear translocation of nuclear erythroid 2 p45-related factor 2 (Nrf2) and elevation of antioxidant protein expression. FGF1△HBS also inhibited activity and/or expression of lipogenic genes, coincident with phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and its substrates. Mechanistic studies on palmitate exposed hepatic cells demonstrated that NAFLD-like oxidative damage and lipid accumulation could be reversed by FGF1△HBS . In palmitate-treated hepatic cells, small interfering RNA (siRNA) knockdown of Nrf2 abolished only FGF1△HBS antioxidative actions but not improvement of lipid metabolism. In contrast, AMPK inhibition by pharmacological agent or siRNA abolished FGF1△HBS benefits on both oxidative stress and lipid metabolism that were FGF receptor (FGFR) 4 dependent. Further support of these in vitro findings is that liver-specific AMPK knockout abolished therapeutic effects of FGF1△HBS against high-fat/high-sucrose diet-induced hepatic steatosis. Moreover, FGF1△HBS improved high-fat/high-cholesterol diet-induced steatohepatitis and fibrosis in apolipoprotein E knockout mice. CONCLUSIONS These findings indicate that FGF1△HBS is effective for preventing and reversing liver steatosis and steatohepatitis and acts by activation of AMPK through hepatocyte FGFR4.

Diabetes mellitus associated dysfunction of endothelial progenitor cells (EPCs) may contribute to dysregulation of endothelial regeneration. Whether oxidative protection of EPCs by an antioxidant, such as the protein metallothionein (MT) can have positive angiogenic effects and by what mechanisms remain unclear. Endothelial-specific MT overexpression (JTMT) mice were made diabetic by high fat diet followed by streptozocin administration (HFD/STZ). Diabetic hind limb ischemia (HLI) was established by femoral artery ligation. Bone marrow mononuclear cells (MNCs) collected from JTMT mice were transplanted into db/db mice with HLI. Blood reperfusion was monitored. High glucose and hypoxia conditions in culture were adopted to mimic diabetic ischemia. Compared with wild-type (WT) littermates, JTMT mice were resistant to diabetes-induced impairment in ischemia angiogenesis and blood reperfusion in HFD/STZ diabetes. Similarly, transplantation of MT overexpressing MNCs showed better therapeutic effect on db/db mice with HLI than transplantation of WT MNCs. These changes were accompanied by increased mobilization and infiltration of EPCs in JTMT mice, and enhanced incorporation of EPCs into capillaries in JTMT MNCs transplanted db/db mice. Furthermore, EPCs from JTMT mice exhibited augmented cell survival, tube formation, and migration capacities under diabetic ischemia-like conditions. Mechanistically, the expression of hypoxia-inducible factor 1α (HIF-1α) and the secretion of stromal cell-derived factor (SDF-1) in blood and expression in ischemic tissues were upregulated in JTMT and JTMT-MNC transplanted db/db mice, and in cultured JTMT EPCs, which were accompanied by marked amelioration of oxidative stress. However, MT-mediated elevation of SDF-1 and improvements of function in EPCs were all abrogated by siRNA knockdown of HIF-1α expression without effect on the anti-oxidative capacity of MT. Endothelial-specific MT elevation is sufficient to protect against diabetes mellitus-induced impairment of ischemia angiogenesis by promoting EPC function. The benefits of MT are predominantly mediated by upregulation of the HIF-1α/SDF-1 pathway.

Aims: Sulforaphane (SFN) as a nuclear factor erythroid 2-related factor 2 (Nrf2) activator protects the heart from, and deletion of the Nrf2 gene exaggerates, the effects of diabetes. Angiotensin II (Ang II) plays a critical role in the development of diabetic cardiomyopathy; therefore, whether SFN prevents Ang II-induced cardiomyopathy through activation of Nrf2 was examined. Methods and Results: The chronic cardiac effects of Ang II with and without SFN were examined in wild-type mice, transgenic Nrf2 knockout (Nrf2-KO) mice, and mice in which cardiac tissue overexpressed Nrf2 (Nrf2-TG). The signaling pathways of SFN-mediated Nrf2 activation were examined in H9C2 cells. Administration of a subpressor dose of Ang II to WT mice induced cardiac oxidative stress, inflammation, remodeling and dysfunction, all of which could be prevented by SFN treatment, which also up-regulated Nrf2 expression and activation. Nrf2-TG mice showed resistance and Nrf2-KO mice displayed resistance to Ang II-induced cardiomyopathy. Meanwhile, the ability of SFN to protect against Ang II-induced cardiac damage was lost in Nrf2-KO mice. Up-regulation and activation of Nrf2 by SFN is accompanied by activation of AKT, inhibition of glycogen synthase kinase (GSK)-3β, and increased nuclear accumulation of Fyn. In vitro up-regulation of Nrf2 by SFN in H9C2 cells was abolished and nuclear Fyn accumulation was increased when cells were exposed to a PI3K inhibitor or GSK-3β-specific activator. Conclusion: Nrf2 plays a central role in the prevention of Ang II-induced pathological effects, and SFN can prevent Ang II-induced cardiomyopathy through activation of Nrf2 partially via the AKT/GSK-3β/Fyn pathway.