Search

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.

Induction of pyruvate dehydrogenase kinase 4 (PDK4) conserves glucose and substrates for gluconeogenesis and thereby helps regulate blood glucose levels during starvation. We report here that retinoic acids (RA) as well as Trichostatin A (TSA), an inhibitor of histone deacetylase (HDAC), regulate PDK4 gene expression. Two retinoic acid response elements (RAREs) to which retinoid X receptor alpha (RXRalpha) and retinoic acid receptor alpha (RARalpha) bind and activate transcription are present in the human PDK4 (hPDK4) proximal promoter. Sp1 and CCAAT box binding factor (CBF) bind to the region between two RAREs. Mutation of either the Sp1 or the CBF site significantly decreases basal expression, transactivation by RXRalpha/RARalpha/RA, and the ability of TSA to stimulate hPDK4 gene transcription. By the chromatin immunoprecipitation assay, RA and TSA increase acetylation of histones bound to the proximal promoter as well as occupancy of CBP and Sp1. Interaction of p300/CBP with E1A completely prevented hPDK4 gene activation by RXRalpha/RARalpha/RA and TSA. The p300/CBP may enhance acetylation of histones bound to the hPDK4 promoter and cooperate with Sp1 and CBF to stimulate transcription of the hPDK4 gene in response to RA and TSA.

In order to identify key genes involved in the development of atherosclerotic lesions, differentially expressed genes in atherosclerotic plaques obtained from diet-induced hypercholesterolemic rabbit aorta were screened using the differential display (DD) RT-PCR technique. Aortic RNAs were isolated from rabbits fed cholesterol-supplemented (2% cholesterol in lab-chow, w/w) chow diet for 12 weeks, followed by the synthesis of cDNAs by reverse-transcription using 2-base anchored oligo (dT) (5'-T11VN) as 3'-primers. Synthesized cDNAs were amplified by PCR using arbitrary 10-mers as 5'-primers and the same 3'-primers used in the reverse-transcription. Amplified cDNAs sized between 0.2 to 0.5kb obtained from control and cholesterol-fed rabbit aortas were displayed on the 6% DNA-sequencing gel for comparisons. The cDNA bands showing distinctive differences in patterns of display or in density of the band were extracted from the gel. A total of 66 differentially displayed cDNAs was isolated and subjected to the reverse-Northern and Northern blot analyses in order to confirm the differences. Through the extensive confirming processes, three cDNAs were finally selected (designated CRGRA-1 through -3) and their nucleotide sequences were determined. Two of those (CRGRA-1 and -2) were determined to be up regulated and the other (CRGRA-3) was down-regulated by the cholesterol-feeding. Upon homology search on databases for the identification of the genes, the first cDNA (CRGRA-1) turned out to be a part of a novel gene, the second one (CRGRA-2) was homologous (82%) to the corresponding segment of mitochondrial NADH dehydrogenase subunits 4 gene, and the last one (CRGRA-2) was identified to be homologous (94%) to a segment of human small GTP-binding protein (Rab7) gene.