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Vascular calcification, a pathologic response to defective calcium and phosphate homeostasis, is strongly associated with cardiovascular mortality and morbidity. In this study, we have observed that pyruvate dehydrogenase kinase 4 (PDK4) is upregulated and pyruvate dehydrogenase complex phosphorylation is increased in calcifying vascular smooth muscle cells (VSMCs) and in calcified vessels of patients with atherosclerosis, suggesting that PDK4 plays an important role in vascular calcification. Both genetic and pharmacological inhibition of PDK4 ameliorated the calcification in phosphate-treated VSMCs and aortic rings and in vitamin D3-treated mice. PDK4 augmented the osteogenic differentiation of VSMCs by phosphorylating SMAD1/5/8 via direct interaction, which enhances BMP2 signaling. Furthermore, increased expression of PDK4 in phosphate-treated VSMCs induced mitochondrial dysfunction followed by apoptosis. Taken together, our results show that upregulation of PDK4 promotes vascular calcification by increasing osteogenic markers with no adverse effect on bone formation, demonstrating that PDK4 is a therapeutic target for vascular calcification.

Abstract-Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are important pathogenic mechanisms in atherosclerosis and restenosis after vascular injury. In this study, we investigated the effects of

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Clinical prescription of cisplatin, one of the most widely used chemotherapeutic agents, is limited by its side effects, particularly tubular injury-associated nephrotoxicity. Since details of the underlying mechanisms are not fully understood, we investigated the role of pyruvate dehydrogenase kinase (PDK) in cisplatin-induced acute kidney injury. Among the PDK isoforms, PDK4 mRNA and protein levels were markedly increased in the kidneys of mice treated with cisplatin, and c-Jun N-terminal kinase activation was involved in cisplatin-induced renal PDK4 expression. Treatment with the PDK inhibitor sodium dichloroacetate (DCA) or genetic knockout of PDK4 attenuated the signs of cisplatin-induced acute kidney injury, including apoptotic morphology of the kidney tubules along with numbers of TUNEL-positive cells, cleaved caspase-3, and renal tubular injury markers. Cisplatin-induced suppression of the mitochondrial membrane potential, oxygen consumption rate, expression of electron transport chain components, cytochrome c oxidase activity, and disruption of mitochondrial morphology were noticeably improved in the kidneys of DCA-treated or PDK4 knockout mice. Additionally, levels of the oxidative stress marker 4-hydroxynonenal and mitochondrial reactive oxygen species were attenuated, whereas superoxide dismutase 2 and catalase expression and glutathione synthetase and glutathione levels were recovered in DCA-treated or PDK4 knockout mice. Interestingly, lipid accumulation was considerably attenuated in DCA-treated or PDK4 knockout mice via recovered expression of peroxisome proliferator-activated receptor-α and coactivator PGC-1α, which was accompanied by recovery of mitochondrial biogenesis. Thus, PDK4 mediates cisplatin-induced acute kidney injury, suggesting that PDK4 might be a therapeutic target for attenuating cisplatin-induced acute kidney injury.

TGF-β plays a key role in the development of renal fibrosis. Suppressing the TGF-β signaling pathway is a possible therapeutic approach for preventing this disease, and reports have suggested that Nrf2 protects against renal fibrosis by inhibiting TGF-β signaling. This study examines whether dimethylfumarate (DMF), which stimulates Nrf2, prevents renal fibrosis via the Nrf2-mediated suppression of TGF-β signaling. Results showed that DMF increased nuclear levels of Nrf2, and both DMF and adenovirus-mediated overexpression of Nrf2 (Ad-Nrf2) decreased PAI-1, alpha-smooth muscle actin (α-SMA), fibronectin and type 1 collagen expression in TGF-β-treated rat mesangial cells (RMCs) and renal fibroblast cells (NRK-49F). Additionally, DMF and Ad-Nrf2 repressed TGF-β-stimulated Smad3 activity by inhibiting Smad3 phosphorylation, which was restored by siRNA-mediated knockdown of Nrf2 expression. However, downregulation of the antioxidant response element (ARE)-driven Nrf2 target genes such as NQO1, HO-1 and glutathione S-transferase (GST) did not reverse the inhibitory effect of DMF on TGF-β-induced upregulation of profibrotic genes or extracellular matrix proteins, suggesting an ARE-independent anti-fibrotic activity of DMF. Finally, DMF suppressed unilateral ureteral obstruction (UUO)-induced renal fibrosis and α-SMA, fibronectin and type 1 collagen expression in the obstructed kidneys from UUO mice, along with increased and decreased expression of Nrf2 and phospho-Smad3, respectively. In summary, DMF attenuated renal fibrosis via the Nrf2-mediated inhibition of TGF-β/Smad3 signaling in an ARE-independent manner, suggesting that DMF could be used to treat renal fibrosis.

Metabolic reprogramming during macrophage polarization supports the effector functions of these cells in health and disease. Here, we demonstrate that pyruvate dehydrogenase kinase (PDK), which inhibits the pyruvate dehydrogenase-mediated conversion of cytosolic pyruvate to mitochondrial acetyl-CoA, functions as a metabolic checkpoint in M1 macrophages. Polarization was not prevented by PDK2 or PDK4 deletion but was fully prevented by the combined deletion of PDK2 and PDK4; this lack of polarization was correlated with improved mitochondrial respiration and rewiring of metabolic breaks that are characterized by increased glycolytic intermediates and reduced metabolites in the TCA cycle. Genetic deletion or pharmacological inhibition of PDK2/4 prevents polarization of macrophages to the M1 phenotype in response to inflammatory stimuli (lipopolysaccharide plus IFN-γ). Transplantation of PDK2/4-deficient bone marrow into irradiated wild-type mice to produce mice with PDK2/4-deficient myeloid cells prevented M1 polarization, reduced obesity-associated insulin resistance, and ameliorated adipose tissue inflammation. A novel, pharmacological PDK inhibitor, KPLH1130, improved high-fat diet-induced insulin resistance; this was correlated with a reduction in the levels of pro-inflammatory markers and improved mitochondrial function. These studies identify PDK2/4 as a metabolic checkpoint for M1 phenotype polarization of macrophages, which could potentially be exploited as a novel therapeutic target for obesity-associated metabolic disorders and other inflammatory conditions.

Excessive proliferation of vascular smooth muscle cells (VSMCs) and incomplete re-endothelialization is a major clinical problem limiting the long-term efficacy of percutaneous coronary angioplasty. We tested if dimethylfumarate (DMF), an anti-psoriasis drug, could inhibit abnormal vascular remodeling via NF−E2-related factor 2 (Nrf2)-NAD(P)H quinone oxidoreductase 1 (NQO1) activity. DMF significantly attenuated neointimal hyperplasia induced by balloon injury in rat carotid arteries via suppression of the G1 to S phase transition resulting from induction of p21 protein in VSMCs. Initially, DMF increased p21 protein stability through an enhancement in Nrf2 activity without an increase in p21 mRNA. Later on, DMF stimulated p21 mRNA expression through a process dependent on p53 activity. However, heme oxygenase-1 (HO-1) or NQO1 activity, well-known target genes induced by Nrf2, were dispensable for the DMF induction of p21 protein and the effect on the VSMC proliferation. Likewise, DMF protected endothelial cells from TNF-α-induced apoptosis and the dysfunction characterized by decreased eNOS expression. With knock-down of Nrf2 or NQO1, DMF failed to prevent TNF-α-induced cell apoptosis and decreased eNOS expression. Also, CD31 expression, an endothelial specific marker, was restored in vivo by DMF. In conclusion, DMF prevented abnormal proliferation in VSMCs by G1 cell cycle arrest via p21 upregulation driven by Nrf2 and p53 activity, and had a beneficial effect on TNF-α-induced apoptosis and dysfunction in endothelial cells through Nrf2–NQO1 activity suggesting that DMF might be a therapeutic drug for patients with vascular disease.