Abstract 054: Deficiency Of Nuclear Receptor Interaction Protein Causes Cardiac Hypertrophy

Abstract

Previously, we demonstrate a novel gene, nuclear receptor interaction protein (NRIP, also named as DCAF6 or IQWD1). We also identify NRIP as a Ca2+- dependent calmodulin binding protein that activates calcineurin phosphatase activity. To investigate insights into in vivo function of NRIP, we generated NRIP-null mice and found that loss of NRIP impairs cardiac function and lead to cardiac hypertrophy progressively. Furthermore, NRIP-/- mice display weaker muscle strength, reduced cardiac function, and cardiac fibrosis compared with WT. To verify the regulation mechanism, we found that α-actinin-2 (ACTN2), which is a biomarker of muscular Z-disc complex, is one of NRIP-interacting proteins from the yeast two-hybrid system. ACTN2 cross-links with actin filament to stabilize sarcomeric structure and muscle contraction, which is an essential constituent of sarcomere. Through the in vitro and in vivo binding assays, we further confirm the interaction and define the interacting domains between NRIP and ACTN2. Plus co-localization of NRIP and ACTN2 is discovered in cardiac tissue by immunofluorescence assays, we firstly define NRIP as a Z-disc protein. Although the Z-disc has been viewed as a passive constituent of the sarcomere traditionally, increasing numbers of mutations in Z-disc proteins leading to disruption and malfunction of the contractile apparatus have been shown to cause cardiomyopathies and/or muscular dystrophies. Hence, we analyzed the sarcomeric structure of NRIP-/- cardiomyocytes and found reduction of I-band width and extension of Z-disc. Besides, we know that NRIP is a Ca2+- dependent calmodulin binding protein. In cardiomyocytes, calmodulin interacts with multiple calcium ion channels or proteins to directly or indirectly regulate the variation of calcium concentration during muscle contraction. Therefore, we isolated and measured the calcium transient of cardiomyocytes. Then, we found that deficiency of NRIP decreases the amplitude of calcium transient. In a conclusion, we speculated that loss of NRIP impairs the structure of sarcomere, the amplitude of calcium transient during muscle contraction and the function of muscle contraction resulting in cardiomyopathy.