Since PI treatment decreased and increased myocardial UPS activity and ubiquitination, respectively, this may lead to an accumulation of contractile protein aggregates and impaired cardiac contractility and signaling pathways. For example, protein turnover of connexin 43, PLB and SERCA-2a are all regulated by the UPS and may explain the higher expression levels found here and before by us. Others have established that altered connexin 43 expression can precede arrhythmias, ventricular fibrillation and incorrect 957054-30-7 signal propagation in the long-term. Therefore we tentatively suggest that elevated connexin 43 expression in our model may results in detrimental effects on contractile function in the future, especially within the context of HIV-AIDS. We previously identified lower myocardial calcium levels and higher SERCA-2a protein expression with PI treatment, and now report attenuated and elevated calmodulin and pPLB expression levels, respectively. In parallel, we found increased myocardial calcineurin and NFAT3 expression levels. Of note, others found that cardiac-specific calcineurin overexpression resulted in enhanced pPLB and SERCA-2a expression and diminished phosphorylation and redistribution of connexin 43. This was associated with depressed contractility and cardiac hypertrophy. Here the authors proposed that connexin 43 may be a downstream target of calcineurin and that attenuated connexin 43 levels may be linked to perturbed gap junction assembly and arrhythmogenesis. We propose that a α-Amatoxin cost similar scenario may exist in our model and that greater calcineurin activation is linked to elevated connexin 43 expression that may compromise gap junction function. Increased SERCA-2a, connexin 43 and pPLB expression may occur as a result of lower myocardial UPS and have also been implicated as downstream transcriptional targets of calcineurin. Thus, elevated connexin 43 and pPLB expression may represent an adaptive response by PI-treated hearts to improve calcium handling, which may improve cardiac function. Higher calcineurin activation also leads to increased dephosphorylation and translocation of NFAT3 to the nucleus for activation of downstream targets, PGC-1a and pro-hypertrophic genes. However, since the calcineurin-NFAT3 pathway did not result in cardiac hypertrophy in our model, we are of the opinion that longer-term activation may eventually result in a hypertrophic response. These findings, however, represent a model of altered cardiac physiology and suggest a potential association with PI-induced molecular alterations to key junction and ionic proteins that may precede the onset of contractile dysfunction.
