Sox6 as a new modulator of renin expression in the kidney.

Juxtaglomerular (JG) cells, major sources of renin, differentiate from metanephric mesenchymal cells that give rise to JG cells or a subset of smooth muscle cells of the renal afferent arteriole. During periods of dehydration and salt deprivation, renal mesenchymal stromal cells (MSCs) differentiate from JG cells. JG cells undergo expansion and smooth muscle cells redifferentiate to express renin along the afferent arteriole. Gene expression profiling comparing resident renal MSCs with JG cells indicates that the transcription factor Sox6 is highly expressed in JG cells in the adult kidney. In vitro, loss of Sox6 expression reduces differentiation of renal MSCs to renin-producing cells. In vivo, Sox6 expression is upregulated after a low-Na+ diet and furosemide. Importantly, knockout of Sox6 in Ren1d+ cells halts the increase in renin-expressing cells normally seen during a low-Na+ diet and furosemide as well as the typical increase in renin. Furthermore, Sox6 ablation in renin-expressing cells halts the recruitment of smooth muscle cells along the afferent arteriole, which normally express renin under these conditions. These results support a previously undefined role for Sox6 in renin expression.

HASF (C3orf58) is a novel ligand of the insulin-like growth factor 1 receptor.

We have recently shown that hypoxia and Akt-induced stem cell factor (HASF) protects the heart from ischemia-induced damage and promotes cardiomyocyte proliferation. While we have identified certain signaling pathways responsible for these protective effects, the receptor mediating these effects was unknown. Here, we undertook studies to identify the HASF receptor. A yeast two-hybrid screen identified a partial fragment of insulin-like growth factor 1 receptor (IGF1R) as a binding partner of HASF. Subsequent co-immunoprecipitation experiments showed that HASF bound to full-length IGF1R. Binding assays revealed a high affinity of HASF for IGF1R. The treatment of neonatal ventricular cardiomyocytes with HASF resulted in the phosphorylation of IGF1R and other proteins known to be involved in IGF1R-mediated signaling pathways. HASF-mediated ERK activation was abrogated by IGF1R pharmacological inhibitors and siRNAs that targeted IGF1R. However, siRNA-mediated knockdown of either IGF2R or the insulin receptor had no effect on HASF-induced cell signaling. Additionally, pharmacologic inhibition of IGF1R impeded HASF's ability to induce cardiomyocyte proliferation. Finally, we documented that in vivo deletion of the IGF1R completely abolished the ability of HASF to promote cardiomyocyte proliferation in an overexpression mouse model providing further evidence in vivo that the IGF1R is the functional receptor for HASF.

Selenium Augments microRNA Directed Reprogramming of Fibroblasts to Cardiomyocytes via Nanog.

We have recently shown that a combination of microRNAs, miR combo, can directly reprogram cardiac fibroblasts into functional cardiomyocytes in vitro and in vivo. However, direct reprogramming strategies are inefficient and slow. Moving towards the eventual goal of clinical application it is necessary to develop new methodologies to overcome these limitations. Here, we report the identification of a specific media composition, reprogramming media (RM), which augmented the effect of miR combo by 5-15-fold depending upon the cardiac marker tested. RM alone was sufficient to strongly induce cardiac gene and protein expression in neonatal tail-tip as well as cardiac fibroblasts. Expression of pluripotency markers Nanog, Oct4, Sox2, and Klf4 was significantly enhanced by RM, with miR combo augmenting the effect further. Knockdown of Nanog by siRNA inhibited the effect of RM on cardiac gene expression. Removal of insulin-transferrin-selenium completely inhibited the effect of reprogramming media upon cardiac gene expression and the addition of selenium to standard culture media recapitulated the effects of RM. Moreover, selenium enhanced the reprogramming efficiency of miR combo.

Abi3bp regulates cardiac progenitor cell proliferation and differentiation.

RATIONALE: Cardiac progenitor cells (CPCs) are thought to differentiate into the major cell types of the heart: cardiomyocytes, smooth muscle cells, and endothelial cells. We have recently identified ABI family, member 3 (NESH) binding protein (Abi3bp) as a protein important for mesenchymal stem cell biology. Because CPCs share several characteristics with mesenchymal stem cells, we hypothesized that Abi3bp would similarly affect CPC differentiation and proliferation. OBJECTIVE: To determine whether Abi3bp regulates CPC proliferation and differentiation. METHODS AND RESULTS: In vivo, genetic ablation of the Abi3bp gene inhibited CPC differentiation, whereas CPC number and proliferative capacity were increased. This correlated with adverse recovery after myocardial infarction. In vitro, CPCs, either isolated from Abi3bp knockout mice or expressing an Abi3bp shRNA construct, displayed a higher proliferative capacity and, under differentiating conditions, reduced expression of both early and late cardiomyocyte markers. Abi3bp controlled CPC differentiation via integrin-ß1, protein kinase C-ζ, and v-akt murine thymoma viral oncogene homolog. CONCLUSIONS: We have identified Abi3bp as a protein important for CPC differentiation and proliferation.