Background/Aims: Morphological and biochemical maladaptation of cardiomyocytes are associated with mitochondrial dysfunction and dysregulation in hypertrophic conditions. Peroxisome proliferator activated receptor α (PPARα), a drug target for dyslipidemia, is known to be downregulated in cardiomyocytes in response to hypertrophic stimuli. The current study was undertaken to investigate the role of PPARα signaling in mitochondrial remodeling and thereby dysregulation of cardiomyocytes due to hypertrophy in vitro. Methods: Rat cardiomyocytes H9c2 (2-1) and neonatal rat ventricular myocytes (NRVMs) were cultured and treated with α₁-adrenergic agonist phenylephrine (PE, 100 µM, 24 hours) in the presence or absence of 10 µM fenofibrate or bezafibrate. Cellular hypertrophy was observed by atomic force microscopy and immunofluorescence with F-actin antibody. mRNA levels of hypertrophic marker genes and other genes were examined by quantitative real time PCR. Structural as well as functional remodeling of the mitochondria were evaluated by immunofluorescence (F-actin and COX-I), live cell imaging microscopy (JC-I, mitotracker), mitochondrial complex V activity, MPTP activity and ATP assay. Oxidative stress was measured by using sensitive fluorescent indicator probes. Cellular and mitochondrial calcium were measured by using fluorescent indicator probes Rhod-2 AM and X-rhod-1 AM, respectively. Targetscan prediction analysis was performed to find out miRNAs as putative regulators of VDAC. Luciferase assay was conducted to confirm binding of miR28 with VDAC. Results: Co-treatment of H9c2(2-1) cells with PE and fenofibrate restricted increase in cell size and expression of marker genes such as atrial-natriuretic peptide (ANP), brain-natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) compared to those with PE alone. Fenofibrate prevented PE-induced down regulation of PPARα-target genes like CPT-I and MCAD. Mitochondrial trans-membrane potential (Δψ_m) and motility were reduced by PE which were significantly checked by fenofibrate. Increased ROS production and calcium level in PE-treated cells were ameliorated by fenofibrate. Mitochondrial activity and ATP generation were reduced by PE which was rescued by fenofibrate. Fenofibrate also prevented PE-induced down regulation of mitochondrial genes like VDAC-I and COX-IV. Expression of several miRNAs was altered in hypertrophic cardiomyocytes which were restored when co-treated with fenofibrate. miR28 was found to target 3’ untranslated region of VDAC-I. Conclusion: Overall, the results demonstrate that PPARα signaling is critically involved in mitochondrial dysfunction in hypertrophic cardiomyocytes in which miR28 plays a pivotal role.

This study elucidates the role of metabolic remodeling in cardiac dysfunction induced by hyperthyroidism. Cardiac hypertrophy, structural remodeling, and expression of the genes associated with fatty acid metabolism were examined in rats treated with triiodothyronine (T 3 ) alone (8 mg/100 g body weight (BW), i.p.) for 15 days or along with a peroxisome proliferator-activated receptor alpha agonist bezafibrate (Bzf; 30 mg/100 g BW, oral) and were found to improve in the Bzf co-treated condition. Ultrastructure of mitochondria was damaged in T 3 -treated rat heart, which was prevented by Bzf co-administration. Hyperthyroidism-induced oxidative stress, reduction in cytochrome c oxidase activity, and myocardial ATP concentration were also significantly checked by Bzf. Heart function studied at different time points during the course of T 3 treatment shows an initial improvement and then a gradual but progressive decline with time, which is prevented by Bzf co-treatment. In summary, the results demonstrate that hyperthyroidism inflicts structural and functional damage to mitochondria, leading to energy depletion and cardiac dysfunction.

Ventricular dysfunction is one of the important side effects of the anti-inflammatory agent, glucocorticoid (GC). The present study was undertaken to examine whether abnormal calcium signaling is responsible for cardiac dysfunction due to an excess of GC hormone. The synthetic GC drug, dexamethasone (DEX), significantly (P!0 . 001, nZ20) increased heart weight to body weight ratio, left ventricular remodeling, and fibrosis. The microarray analysis showed altered expression of several genes encoding calcium cycling/ion channel proteins in DEXtreated rat heart. The altered expression of some of the genes was validated by real-time PCR and western blotting analyses. The expression of the L-type calcium channels and calsequestrin was increased, whereas sarcoendoplasmic reticulum calcium transport ATPase 2a (SERCA2a) and junctin mRNAs were significantly reduced in DEX-treated rat left ventricular tissues. In neonatal rat ventricular cardiomyocytes, DEX also increased the level of mRNAs of atrial-and brain natriuretic peptides, L-type calcium channels, and calsequestrin after 24 h of treatment, which were mostly restored by mifepristone. The caffeine-induced calcium release was prolonged by DEX compared to the sharp release in control cardiomyocytes. Taken together, these data show that impaired calcium kinetics may be responsible for cardiac malfunction by DEX. The results are important in understanding the pathophysiology of the heart in patients treated with excess GC.

Cardiac hypertrophy is characterized by an increase in the size of the cardiomyocytes which is initially triggered as an adaptive response but ultimately becomes maladaptive with chronic exposure to different hypertrophic stimuli. Prolonged cardiac hypertrophy is often associated with mitochondrial dysfunctions and cardiomyocyte cell death. Peroxisome proliferator activated receptor alpha (PPAR α), which is critical for mitochondrial biogenesis and fatty acid oxidation, is down regulated in hypertrophied cardiomyocytes. Yet, the role of PPAR α in cardiomyocyte death is largely unknown. To assess the role of PPAR α in chronic hypertrophy, isoproterenol, a β-adrenergic receptor agonist was administered in PPAR α knock out (PPAR α−/−) mice for 2 weeks and hypertrophy associated changes in cardiac tissues were observed. Echocardiographic analysis ensured the development of cardiac hypertrophy and compromised hemodynamics in PPAR α−/− mice. Proteomic analysis using high resolution mass spectrometer identified about 1,200 proteins enriched in heart tissue. Proteins were classified according to biological pathway and molecular functions. We observed an unexpected down regulation of apoptotic markers, Annexin V and p53 in hypertrophied heart tissue. Further validation revealed a significant down regulation of apoptosis regulator, PTEN, along with other apoptosis markers like p53, Caspase 9 and c-PARP. The autophagy markers Atg3, Atg5, Atg7, p62, Beclin1 and LC3 A/B were up regulated in PPAR α−/− mice indicating an increase in autophagy. Similar observations were made in a high cholesterol diet fed PPAR α−/−mice. The results were further validated in vitro using NRVMs and H9C2 cell line by blocking PPAR α that resulted in enhanced autophagosome formation upon hypertrophic stimulation. The results demonstrate that in the absence of PPAR α apoptotic pathway is inhibited while autophagy is enhanced. The data suggest that PPAR α signaling might act as a molecular switch between apoptosis and autophagy thereby playing a critical role in adaptive process in cardiac hypertrophy.

Triazine-aryl-bis-indole derivative inhibits phosphodiesterase activity.