Smyd1, a muscle-specific histone methyltransferase, has established roles in skeletal and cardiac muscle development, but its role in the adult heart remains poorly understood. Our prior work demonstrated that cardiac-specific deletion of Smyd1 in adult mice (Smyd1-KO) leads to hypertrophy and heart failure. Here we show that down-regulation of mitochondrial energetics is an early event in these Smyd1-KO mice preceding the onset of structural abnormalities. This early impairment of mitochondrial energetics in Smyd1-KO mice is associated with a significant reduction in gene and protein expression of PGC-1α, PPARα, and RXRα, the master regulators of cardiac energetics. The effect of Smyd1 on PGC-1α was recapitulated in primary cultured rat ventricular myocytes, in which acute siRNA-mediated silencing of Smyd1 resulted in a greater than twofold decrease in PGC-1α expression without affecting that of PPARα or RXRα. In addition, enrichment of histone H3 lysine 4 trimethylation (a mark of gene activation) at the PGC-1α locus was markedly reduced in Smyd1-KO mice, and Smyd1-induced transcriptional activation of PGC-1α was confirmed by luciferase reporter assays. Functional confirmation of Smyd1's involvement showed an increase in mitochondrial respiration capacity induced by overexpression of Smyd1, which was abolished by siRNA-mediated PGC-1α knockdown. Conversely, overexpression of PGC-1α rescued transcript expression and mitochondrial respiration caused by silencing Smyd1 in cardiomyocytes. These findings provide functional evidence for a role of Smyd1, or any member of the Smyd family, in regulating cardiac energetics in the adult heart, which is mediated, at least in part, via modulating PGC-1α.

Metabolic adaption is crucial for the heart to sustain its contractile activity under various physiological and pathological conditions. At the molecular level, the changes in energy demand impinge on the expression of genes encoding for metabolic enzymes. Among the major components of an intricate transcriptional circuitry, peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC-1α) plays a critical role as a metabolic sensor, which is responsible for the fine-tuning of transcriptional responses to a plethora of stimuli. Cumulative evidence suggests that energetic impairment in heart failure is largely attributed to the dysregulation of PGC-1α. In this review, we summarize recent studies revealing how PGC-1α is regulated by a multitude of mechanisms, operating at different regulatory levels, which include epigenetic regulation, the expression of variants, post-transcriptional inhibition, and post-translational modifications. We further discuss how the PGC-1α regulatory cascade can be impaired in the failing heart.

The transcriptional regulatory machinery in mitochondrial bioenergetics is complex and is still not completely understood. We previously demonstrated that the histone methyltransferase Smyd1 regulates mitochondrial energetics. Here, we identified Perm1 (PPARGC-1 and ESRR-induced regulator, muscle specific 1) as a downstream target of Smyd1 through RNA-seq. Chromatin immunoprecipitation assay showed that Smyd1 directly interacts with the promoter of Perm1 in the mouse heart, and this interaction was significantly reduced in mouse hearts failing due to pressure overload for 4 weeks, where Perm1 was downregulated (24.4 ± 5.9% of sham, p<0.05). Similarly, the Perm1 protein level was significantly decreased in patients with advanced heart failure (55.2 ± 13.1% of donors, p<0.05). Phenylephrine (PE)-induced hypertrophic stress in cardiomyocytes also led to downregulation of Perm1 (55.7 ± 5.7% of control, p<0.05), and adenovirus-mediated overexpression of Perm1 rescued PE-induced downregulation of estrogen-related receptor alpha (ERRα), a key transcriptional regulator of mitochondrial energetics, and its target gene, Ndufv1 (Complex I). Pathway enrichment analysis of cardiomyocytes in which Perm1 was knocked-down by siRNA (siPerm1), revealed that the most downregulated pathway was metabolism. Cell stress tests using the Seahorse XF analyzer showed that basal respiration and ATP production were significantly reduced in siPerm1 cardiomyocytes (40.7% and 23.6% of scrambled-siRNA, respectively, both p<0.05). Luciferase reporter gene assay further revealed that Perm1 dose-dependently increased the promoter activity of the ERRα gene and known

The “stress” kinases cAMP-dependent protein kinase (PKA) and calcium/calmodulin-dependent protein kinase II (CaMKII), phosphorylate the Na+ channel Nav1.5 subunit to regulate its function. However, how the channel regulation translates to ventricular conduction is poorly understood. We hypothesized that the stress kinases positively and differentially regulate conduction in the right (RV) and the left (LV) ventricles. We applied the CaMKII blocker KN93 (2.75 μM), PKA blocker H89 (10 μM), and broad-acting phosphatase blocker calyculin (30 nM) in rabbit hearts paced at a cycle length (CL) of 150-8,000 ms. We used optical mapping to determine the distribution of local conduction delays (inverse of conduction velocity). Control hearts exhibited constant and uniform conduction at all tested CLs. Calyculin (15-min perfusion) accelerated conduction, with greater effect in the RV (by 15.3%) than in the LV (by 4.1%; P < 0.05). In contrast, both KN93 and H89 slowed down conduction in a chamber-, time-, and CL-dependent manner, with the strongest effect in the RV outflow tract (RVOT). Combined KN93 and H89 synergistically promoted conduction slowing in the RV (KN93: 24.7%; H89: 29.9%; and KN93 + H89: 114.2%; P = 0.0016) but not the LV. The progressive depression of RV conduction led to conduction block and reentrant arrhythmias. Protein expression levels of both the CaMKII-δ isoform and the PKA catalytic subunit were higher in the RVOT than in the apical LV ( P < 0.05). Thus normal RV conduction requires a proper balance between kinase and phosphatase activity. Dysregulation of this balance due to pharmacological interventions or disease is potentially proarrhythmic. NEW & NOTEWORTHY We show that uniform ventricular conduction requires a precise physiological balance of the activities of calcium/calmodulin-dependent protein kinase II (CaMKII), PKA, and phosphatases, which involves region-specific expression of CaMKII and PKA. Inhibiting CaMKII and/or PKA activity elicits nonuniform conduction depression, with the right ventricle becoming vulnerable to the development of conduction disturbances and ventricular fibrillation/ventricular tachycardia.

Tumor necrosis factor-α (TNF-α) is a pleiotropic inflammatory cytokine that exerts potent cytotoxic effects on solid tumor cells, while not affecting their normal counterparts. It is also known that TNF-α exerts many of its biological functions via interaction with specific receptors. To understand the potential roles of intrinsic disorder in the functioning of this important cytokine, we explored the peculiarities of intrinsic disorder distribution in human TNF-α and its homologs from various species, ranging from zebrafish to chimpanzee. We also studied the peculiarities of intrinsic disorder distribution in human TNF-α receptors, TNFR1 and TNFR2. Analysis revealed that cytoplasmic domains of TNF-α and its receptors are expected to be highly disordered. Furthermore, although the sequence identities of analyzed TNF-α homologs range from 99.57% (between human and chimpanzee proteins) to 22.33% (between frog and fish proteins), their intrinsic disorder profiles are characterized by a remarkable similarity. These observations indicate that the peculiarities of distribution of the intrinsic disorder propensity within the amino acid sequences are evolutionary conserved, and therefore could be of functional importance for this family of proteins. We also show that disordered and flexible regions of human TNF-α and its TNFR1 and TNFR2 receptors are crucial for some of their biological activities.