8.A.110.1.4
Junctophilin-2, JPH2 or JP2, of 696 aas and 2 TMSs, N- and C-terminal. It is a structural membrane protein that tethers T-tubules to the sarcoplasmic reticulum to allow coordinated calcium-induced calcium release in cardiomyocytes (Chan et al. 2019). Defective excitation-contraction coupling in myocardial ischemia-reperfusion (IR) injury is associated with junctophilin-2 proteolysis. Matrix metalloproteinase-2 (MMP-2) is a zinc and calcium-dependent protease that is activated by oxidative stress in myocardial IR injury and cleaves both intracellular and extracellular substrates. Junctophilin-2 is targeted by MMP-2, an MMP inhibitor, ARP-100, was used. IR injury impaired the recovery of cardiac contractile function which was associated with increased degradation of junctophilin-2 and damaged cardiac dyads. In IR hearts, ARP-100 improved the recovery of cardiac contractile function, attenuated junctophilin-2 proteolysis, and prevented ultrastructural damage to the dyad. MMP-2 was co-localized with junctophilin-2 in aerobic and IR hearts by immunoprecipitation and immunohistochemistry. In situ zymography showed that MMP activity was localized to the Z-disc and sarcomere in aerobic hearts and accumulated at sites where the striated JPH-2 staining was disrupted in IR hearts. In vitro proteolysis assays showed that junctophilin-2 is susceptible to proteolysis by MMP-2 with multiple MMP-2 cleavage sites between the membrane occupation and recognition nexus repeats and within the divergent region of junctophilin-2. Degradation of junctophilin-2 by MMP-2 is an early consequence of myocardial IR injury which may initiate a cascade of sequelae leading to impaired contractile function (Chan et al. 2019). S-Palmitoylation of junctophilin-2 is critical for its role in tethering the sarcoplasmic reticulum to the plasma membrane (Jiang et al. 2019).