YAP activation promotes the transdifferentiation of cardiac fibroblasts to myofibroblasts in matrix remodeling of dilated cardiomyopathy

Yes-associated protein (YAP) is an important regulator of cellular proliferation and transdifferentiation. However, little is known about the mechanisms underlying myofibroblast transdifferentiation in dilated cardiomyopathy (DCM). We investigated the role of YAP in the pathological process of cardiac matrix remodeling. A classic model of DCM was established in BALB/c mice by immunization with porcine cardiac myosin. Cardiac fibroblasts were isolated from neonatal Sprague-Dawley rats by density gradient centrifugation. The expression levels of α-smooth muscle actin (α-SMA) and collagen volume fraction (CVF) were significantly increased in DCM mice. Angiotensin II (Ang II)-mediated YAP activation promoted the proliferation and transdifferentiation of neonatal rat cardiac fibroblasts, and this effect was significantly suppressed in the shRNA YAP + Ang II group compared with the shRNA Control + Ang II group in vitro (2.98±0.34 ×105 vs 5.52±0.82 ×105, P<0.01). Inhibition of endogenous Ang II-stimulated YAP improved the cardiac function by targeting myofibroblast transdifferentiation to attenuate matrix remodeling in vivo. In the valsartan group, left ventricular ejection fraction and fractional shortening were significantly increased compared with the DCM group (52.72±5.51% vs 44.46±3.01%, P<0.05; 34.84±3.85% vs 26.65±3.12%, P<0.01). Our study demonstrated that YAP was a regulator of cardiac myofibroblast differentiation, and regulation of YAP signaling pathway contributed to improve cardiac function of DCM mice, possibly in part by decreasing myofibroblast transdifferentiation to inhibit matrix remodeling.

Biphasic modulation of insulin receptor substrate-1 during goitrogenesis

Insulin receptor substrate-1 (IRS-1) is the main intracellular substrate for both insulin and insulin-like growth factor I (IGF-I) receptors and is critical for cell mitogenesis. Thyrotropin is able to induce thyroid cell proliferation through the cyclic AMP intracellular cascade; however, the presence of either insulin or IGF-I is required for the mitogenic effect of thyroid-stimulating hormone (TSH) to occur. The aim of the present study was to determine whether thyroid IRS-1 content is modulated by TSH in vivo. Strikingly, hypothyroid goitrous rats, which have chronically high serum TSH levels (control, C = 2.31 ± 0.28; methimazole (MMI) 21d = 51.02 ± 6.02 ng/mL, N = 12 rats), when treated with 0.03 percent MMI in drinking water for 21 days, showed significantly reduced thyroid IRS-1 mRNA content. Since goiter was already established in these animals by MMI for 21 days, we also evaluated IRS-1 expression during goitrogenesis. Animals treated with MMI for different periods of time showed a progressive increase in thyroid weight (C = 22.18 ± 1.21; MMI 5d = 32.83 ± 1.48; MMI 7d = 31.1 ± 3.25; MMI 10d = 33.8 ± 1.25; MMI 14d = 45.5 ± 2.56; MMI 18d = 53.0 ± 3.01; MMI 21d = 61.9 ± 3.92 mg, N = 9-15 animals per group) and serum TSH levels (C = 1.57 ± 0.2; MMI 5d = 9.95 ± 0.74; MMI 7d = 10.38 ± 0.84; MMI 10d = 17.72 ± 1.47; MMI 14d = 25.65 ± 1.23; MMI 18d = 35.38 ± 3.69; MMI 21d = 31.3 ± 2.7 ng/mL, N = 9-15 animals per group). Thyroid IRS-1 mRNA expression increased progressively during goitrogenesis, being significantly higher by the 14th day of MMI treatment, and then started to decline, reaching the lowest values by the 21st day, when a significant reduction was detected. In the liver of these animals, however, a significant decrease of IRS-1 mRNA was detected after 14 days of MMI treatment, a mechanism probably involved in the insulin resistance that occurs in hypothyroidism. The increase in IRS-1 expression during goitrogenesis may represent...