Regulation of extracellular matrix homeostasis via amino acid-operated cation channels

体内的氨基酸不仅作为蛋白质的组成部分，而且还作为激活细胞内营养信号的特定配体发挥作用。虽然体内氨基酸平衡失调与多种疾病的发生有关，但将氨基酸失衡与疾病直接联系起来的分子靶点(S)尚未确定。我们发现了由细胞外基质组成的氨基酸直接激活的脯氨酸激活的阳离子通道(PRAC)，这些氨基酸包括：脯氨酸、羟脯氨酸、丙氨酸和甘氨酸。我们证实，在原代培养的心肌细胞和心脏成纤维细胞中，二酰甘油激活的瞬时受体潜伏期通道(TRPC3和TRPC6)作为PRAC的主要成分参与其中。TRPC3或TRPC6的缺失取消了氨基酸诱导的阳离子内流和随后细胞内钙离子浓度的增加。我们还发现，在TRPC3和TRPC6缺陷的小鼠心脏以及用TRPC3/6抑制剂处理的心肌细胞中，显著诱导了自噬。这些发现有力地表明，PRAC在心脏的蛋白质循环中起着关键作用。另一方面，在PRAC不表达的细胞中，TRPC3和TRPC6的过表达增加了对氨基酸诱导的钙信号的敏感性。这些结果有力地表明TRPC3/6异源多聚体通道具有PRAC的功能。

Amino acids in vivo work not only as components of proteins, but also specificligands activating intracellular nutrition signalings. Although collapse of amino acid balance in vivo has been implicated in the development of several diseases, molecular target(s) connecting amino acid imbalance directly to diseases have not been identified. We identified proline-activated cation channel (PRAC), which is directly activated by extracellular matrix-composing amino acids, such as proline, hydroxyproline, alanine, and glycine. We demonstrated that diacylglycerol-activated transient receptor potential canonical (TRPC) channels (TRPC3 and TRPC6) participated as major components of PRAC in primary-cultured cardiomyocytes and cardiac fibroblasts. Deletion of TRPC3 or TRPC6 abolished amino acid-induced cation influx and subsequent increase in intracellular Ca2+concentration. We also found that autophagy was significantly induced in TRPC3- and TRPC6-deficient mouse hearts, and in cardiomyocytes treated with TRPC3/6 inhibitor. These findings strongly suggest that PRAC plays a critical role in protein recycling in the heart. On the other hand, overexpression of TRPC3 and TRPC6 conferred susceptibility to amino acid -induced Ca2+signaling in PRAC-nonexpressing cells. These results strongly suggest that TRPC3/6 heteromultimer channels function as PRAC.