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Bcl2‐associated athanogene 3 (BAG3) is a 575 amino acid protein that is found predominantly in the heart, skeletal muscle, and many cancers. Deletions and truncations in BAG3 that result in haplo‐insufficiency have been associated with the development of dilated cardiomyopathy. To study the cellular and molecular events attributable to BAG3 haplo‐insufficiency we generated a mouse in which one allele of BAG3 was flanked by loxP recombination sites (BAG3fl/+). Mice were crossed with α‐MHC‐Cre mice in order to generate mice with cardiac‐specific haplo‐insufficiency (cBAG3+/−) and underwent bi–weekly echocardiography to assess their cardiac phenotype. By 10 weeks of age, cBAG3+/− mice demonstrated increased heart size and diminished left ventricular ejection fraction when compared with non‐transgenic littermates (Cre−/−BAG3fl/+). Contractility in adult myocytes isolated from cBAG3+/− mice were similar to those isolated from control mice at baseline, but showed a significantly decreased response to adrenergic stimulation. Intracellular calcium ([Ca2+]i) transient amplitudes in myocytes isolated from cBAG3+/− mice were also similar to myocytes isolated from control mice at baseline but were significantly lower than myocytes from control mice in their response to isoproterenol. BAG3 haplo‐insufficiency was also associated with decreased autophagy flux and increased apoptosis. Taken together, these results suggest that mice in which BAG3 has been deleted from a single allele provide a model that mirrors the biology seen in patients with heart failure and BAG3 haplo‐insufficiency. [ABSTRACT FROM AUTHOR]

The mechanisms by which Trpm2 channels enhance mitochondrial bioenergetics and protect against oxidative stress‐induced cardiac injury remain unclear. Here, the role of proline‐rich tyrosine kinase 2 (Pyk2) in Trpm2 signaling is explored. Activation of Trpm2 in adult myocytes with H2O2 resulted in 10‐ to 21‐fold increases in Pyk2 phosphorylation in wild‐type (WT) myocytes which was significantly lower (~40%) in Trpm2 knockout (KO) myocytes. Pyk2 phosphorylation was inhibited (~54%) by the Trpm2 blocker clotrimazole. Buffering Trpm2‐mediated Ca2+ increase with 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid (BAPTA) resulted in significantly reduced pPyk2 in WT but not in KO myocytes, indicating Ca2+ influx through activated Trpm2 channels phosphorylated Pyk2. Part of phosphorylated Pyk2 translocated from cytosol to mitochondria which has been previously shown to augment mitochondrial Ca2+ uptake and enhance adenosine triphosphate generation. Although Trpm2‐mediated Ca2+ influx phosphorylated Ca2+‐calmodulin kinase II (CaMKII), the CaMKII inhibitor KN93 did not significantly affect Pyk2 phosphorylation in H2O2‐treated WT myocytes. After ischemia/reperfusion (I/R), Pyk2 phosphorylation and its downstream prosurvival signaling molecules (pERK1/2 and pAkt) were significantly lower in KO‐I/R when compared with WT‐I/R hearts. After hypoxia/reoxygenation, mitochondrial membrane potential was lower and superoxide level was higher in KO myocytes, and were restored to WT values by the mitochondria‐targeted superoxide scavenger MitoTempo. Our results suggested that Ca2+ influx via tonically activated Trpm2 phosphorylated Pyk2, part of which translocated to mitochondria, resulting in better mitochondrial bioenergetics to maintain cardiac health. After I/R, Pyk2 activated prosurvival signaling molecules and prevented excessive increases in reactive oxygen species, thereby affording protection from I/R injury. [ABSTRACT FROM AUTHOR]

The pathophysiology of human immunodeficiency virus (HIV)‐associated cardiomyopathy remains uncertain. We used HIV‐1 transgenic (Tg26) mice to explore mechanisms by which HIV‐related proteins impacted on myocyte function. Compared to adult ventricular myocytes isolated from nontransgenic (wild type [WT]) littermates, Tg26 myocytes had similar mitochondrial membrane potential (ΔΨm) under normoxic conditions but lower Δ Ψm after hypoxia/reoxygenation (H/R). In addition, Δ Ψm in Tg26 myocytes failed to recover after Ca 2+ challenge. Functionally, mitochondrial Ca 2+ uptake was severely impaired in Tg26 myocytes. Basal and maximal oxygen consumption rates (OCR) were lower in normoxic Tg26 myocytes, and further reduced after H/R. Complex I subunit and ATP levels were lower in Tg26 hearts. Post‐H/R, mitochondrial superoxide (O 2•–) levels were higher in Tg26 compared to WT myocytes. Overexpression of B‐cell lymphoma 2‐associated athanogene 3 (BAG3) reduced O 2•– levels in hypoxic WT and Tg26 myocytes back to normal. Under normoxic conditions, single myocyte contraction dynamics were similar between WT and Tg26 myocytes. Post‐H/R and in the presence of isoproterenol, myocyte contraction amplitudes were lower in Tg26 myocytes. BAG3 overexpression restored Tg26 myocyte contraction amplitudes to those measured in WT myocytes post‐H/R. Coimmunoprecipitation experiments demonstrated physical association of BAG3 and the HIV protein Tat. We conclude: (a) Under basal conditions, mitochondrial Ca 2+ uptake, OCR, and ATP levels were lower in Tg26 myocytes; (b) post‐H/R, Δ Ψm was lower, mitochondrial O 2•– levels were higher, and contraction amplitudes were reduced in Tg26 myocytes; and (c) BAG3 overexpression decreased O 2•– levels and restored contraction amplitudes to normal in Tg26 myocytes post‐H/R in the presence of isoproterenol. The hemizygous NL4‐3 Δgag/pol transgenic (Tg26) mouse with replication‐deficient, noninfectious human immunodeficiency virus type 1 (HIV‐1) but with HIV‐1 proteins present in tissues simulates contemporary HIV‐1‐infected patients treated with combination antiretroviral therapy and is an excellent model to study chronic complications of HIV‐1 infection such as HIV‐associated cardiomyopathy. Cardiac myocytes isolated from Tg26 mice demonstrate mitochondrial dysfunction and elevated reactive oxygen species (ROS) that are exacerbated by hypoxia/reoxygenation and adrenergic stress. B‐cell lymphoma 2‐associated athanogene 3 (BAG3) regulates autophagy, apoptosis, excitation‐contraction coupling, mitochondrial quality control, and sarcomere stability in cardiac myocytes and can associate with the HIV‐1 protein Tat. Overexpression of BAG3 in Tg26 myocytes restores the elevated ROS levels to normal and improves contractile dysfunction. BAG3 may be a useful therapeutic modality in the treatment of HIV‐associated cardiomyopathy. [ABSTRACT FROM AUTHOR]