Cardiac hypertrophy(CH)is characterized by an increase in cardiomyocyte size,and is the most common cause of cardiac-related sudden death.A decrease in gap junction(GJ)coupling and mitochondrial dysfunction are important features of CH,but the mechanisms of decreased coupling and energy impairment are poorly understood.It has been reported that GJA1-20k has a strong tropism for mitochondria and is required for the trafficking of connexin 43(Cx43)to cell-cell borders.In this study,we investigated the effects of GJA1-20k on Cx43 GJ coupling and mitochondrial function in the pathogenesis of CH.We performed hematoxylin-eosin(HE)and Masson staining,and observed significant CH in 18-week-old male spontaneously hypertensive rats(SHRs)compared to age-matched normotensive Wistar-Kyoto(WKY)rats.In cardiomyocytes from SHRs,the levels of Cx43 at the intercalated disc(ID)and the expression of GJA1-20k were significantly reduced,whereas JAK-STAT signaling was activated.Furthermore,the SHR rats displayed suppressed mitochondrial GJA1-20k and mitochondrial biogenesis.Administration of valsartan(10 mg·kg-1 d-1,i.g.,for 8 weeks)prevented all of these changes.In neonatal rat cardiomyocytes(NRCMs),overexpression of GJA1-20k attenuated Ang Ⅱ-induced cardiomyocyte hypertrophy and caused elevated levels of GJ coupling at the cell-cell borders.Pretreatment of NRCMs with the Jak2 inhibitor AG490(10 μM)blocked Ang Il-induced reduction in GJA1-20k expression and Cx43 gap junction formation;knockdown of Jak2 in NRCMs significantly lessened Ang Il-induced cardiomyocyte hypertrophy and normalized GJA1-20k expression and Cx43 gap junction formation.Overexpression of GJA1-20k improved mitochondrial membrane potential and respiration and lowered ROS production in Ang Il-induced cardiomyocyte hypertrophy.These results demonstrate the importance of GJA1-20k in regulating gap junction formation and mitochondrial function in Ang Il-induced cardiomyocyte hypertrophy,thus providing a novel therapeutic strategy for patients with cardiomyocyte hypertrophy.