Publications

Sudden cardiac death due to abnormal heart rhythm kills 400,000-460,000 Americans each year. To identify genes that regulate heart rhythm, we are developing a screen that uses mouse embryonic stem cells (mESCs) with gene disruptions that can be differentiated into cardiac cells for phenotyping. Here, we show that the heterozygous disruption of the Akap10 (D-AKAP2) gene that disrupts the final 51 aa increases the contractile response of cultured cardiac cells to cholinergic signals. In both heterozygous and homozygous mutant mice derived from these mESCs, the same Akap10 disruption increases the cardiac response to cholinergic signals, suggesting a dominant interfering effect of the Akap10 mutant allele. The mutant mice have cardiac arrhythmias and die prematurely. We also found that a common variant of AKAP10 in humans (646V, 40% of alleles) was associated with increased basal heart rate and decreased heart rate variability (markers of low cholinergic/vagus nerve sensitivity). These markers predict an increased risk of sudden cardiac death. Although the molecular mechanism remains unknown, our findings in mutant mESCs, mice, and a common human AKAP10 SNP all suggest a role for AKAP10 in heart rhythm control. Our stem cell-based screen may provide a means of identifying other genes that control heart rhythm.

There is increasing evidence that epithelial-vascular interactions are essential for tissue patterning. Here we identified components of the molecular cross talk between respiratory epithelial cells and pulmonary capillaries necessary for the formation of the gas exchange surface of the lung. Selective inactivation of the Vegf-A gene in respiratory epithelium results in an almost complete absence of pulmonary capillaries, demonstrating the dependence of pulmonary capillary development on epithelium-derived Vegf-A. Deficient capillary formation in Vegf-A deficient lungs is associated with a defect in primary septae formation, a morphogenetic process critical for distal lung morphogenesis, coupled with suppression of epithelial cell proliferation and decreased hepatocyte growth factor (Hgf) expression. Lung endothelial cells express Hgf, and selective deletion of the Hgf receptor gene in respiratory epithelium phenocopies the malformation of septae, confirming the requirement for epithelial Hgf signaling in normal septae formation and suggesting that Hgf serves as an endothelium-derived factor that signals to the epithelium. Our findings support a mechanism for primary septae formation dependent on reciprocal interactions between respiratory epithelium and the underlying vasculature, establishing the dependence of pulmonary capillary development on epithelium-derived Vegf-A, and identify Hgf as a putative endothelium-derived factor that mediates the reciprocal signaling from the vasculature to the respiratory epithelium.