In noncontractile cells, increases in intracellular Ca2+ concentration serve as a second messenger to signal proliferation, differentiation, metabolism, motility, and cell death. Many of these Ca2+-dependent regulatory processes operate in cardiomyocytes, although it remains unclear how Ca2+ serves as a second messenger given the high Ca2+ concentrations that control contraction. T-type Ca2+ channels are reexpressed in adult ventricular myocytes during pathologic hypertrophy, although their physiologic function remains unknown. Here we generated cardiac-specific transgenic mice with inducible expression of α1G, which generates Cav3.1 current, to investigate whether this type of Ca2+ influx mechanism regulates the cardiac hypertrophic response. Unexpectedly, α1G transgenic mice showed no cardiac pathology despite large increases in Ca2+ influx, and they were even partially resistant to pressure overload–, isoproterenol-, and exercise-induced cardiac hypertrophy. Conversely, α1G–/– mice displayed enhanced hypertrophic responses following pressure overload or isoproterenol infusion. Enhanced hypertrophy and disease in α1G–/– mice was rescued with the α1G transgene, demonstrating a myocyte-autonomous requirement of α1G for protection. Mechanistically, α1G interacted with NOS3, which augmented cGMP-dependent protein kinase type I activity in α1G transgenic hearts after pressure overload. Further, the anti-hypertrophic effect of α1G overexpression was abrogated by a NOS3 inhibitor and by crossing the mice onto the Nos3–/– background. Thus, cardiac α1G reexpression and its associated pool of T-type Ca2+ antagonize cardiac hypertrophy through a NOS3-dependent signaling mechanism.
Hiroyuki Nakayama, Ilona Bodi, Robert N. Correll, Xiongwen Chen, John Lorenz, Steven R. Houser, Jeffrey Robbins, Arnold Schwartz, Jeffery D. Molkentin