Ablation of miRNA-22 protects against obesity-induced adipocyte senescence and ameliorates metabolic disorders in middle-aged mice.

High-fat diet (HFD) promotes obesity-related metabolic complications by activating cellular senescence in white adipose tissue (WAT). Growing evidence supports the importance of microRNA-22 (miR-22) in metabolic disorders and cellular senescence. Recently, we showed that miR-22 deletion attenuates obesity-related metabolic abnormalities. However, whether miR-22 mediates HFD-induced cellular senescence of WAT remains unknown. Here, we uncovered that obese mice displayed increased pri-miR-22 levels and cellular senescence in WAT. However, miR-22 ablation protected mice against HFD-induced WAT senescence. In addition, in vitro studies showed that miR-22 deletion prevented preadipocyte senescence in response to Doxorubicin (Doxo). Loss-of-function studies in vitro and in vivo revealed that miR-22 increases H2ax mRNA and γH2ax levels in preadipocytes and WAT without inducing DNA damage. Intriguingly, miR-22 ablation prevented HFD-induced increase in γH2ax levels and DNA damage in WAT. Similarly, miR-22 deletion prevented Doxo-induced increase in γH2ax levels in preadipocytes. Adipose miR-22 levels were enhanced in middle-aged mice fed a HFD than those found in young mice. Furthermore, miR-22 deletion attenuated fat mass gain and glucose imbalance induced by HFD in middle-aged mice. Overall, our findings indicate that miR-22 is a key regulator of obesity-induced WAT senescence and metabolic disorders in middle-aged mice.

Set7 deletion attenuates isoproterenol-induced cardiac fibrosis and delays cardiac dysfunction.

Cardiovascular diseases are the main cause of death worldwide. Recent studies have revealed the influence of histone-modifying enzymes in cardiac remodeling and heart dysfunction. The Set7 methyltransferase regulates the expression of several genes through the methylation of histones and modulates the activity of non-histone proteins. However, the role of Set7 in cardiac remodeling and heart dysfunction remains unknown. To address this question, wild-type (WT) and Set7 knockout (KO) male mice were injected with isoproterenol or saline. WT mice injected with isoproterenol displayed a decrease in Set7 activity in the heart. In addition, WT and Set7 KO mice injected with isoproterenol exhibited cardiac hypertrophy. Interestingly, Set7 deletion exacerbated cardiac hypertrophy in response to isoproterenol but attenuated myocardial fibrosis. Echocardiograms revealed that WT mice injected with isoproterenol had lowered ejection fractions and fractional shortening, and increased E'-wave deceleration time and E/A ratio compared with their controls. Conversely, Set7 KO mice did not show alteration in these parameters in response to isoproterenol. However, prolonged exposure to isoproterenol induced cardiac dysfunction both in WT and Set7 KO mice. Both isoproterenol and Set7 deletion changed the transcriptional profile of the heart. Moreover, Set7 deletion increased the expression of Pgc1α and mitochondrial DNA content in the heart, and reduced the expression of cellular senescence and inflammation markers in response to isoproterenol. Taken together, our data suggest that Set7 deletion attenuates isoproterenol-induced myocardial fibrosis and delays heart dysfunction, suggesting that Set7 plays an important role in cardiac remodeling and dysfunction in response to stress.

M-protein is down-regulated in cardiac hypertrophy driven by thyroid hormone in rats.

Although it is well known that the thyroid hormone (T3) is an important positive regulator of cardiac function over a short term and that it also promotes deleterious effects over a long term, the molecular mechanisms for such effects are not yet well understood. Because most alterations in cardiac function are associated with changes in sarcomeric machinery, the present work was undertaken to find novel sarcomeric hot spots driven by T3 in the heart. A microarray analysis indicated that the M-band is a major hot spot, and the structural sarcomeric gene coding for the M-protein is severely down-regulated by T3. Real-time quantitative PCR-based measurements confirmed that T3 (1, 5, 50, and 100 physiological doses for 2 days) sharply decreased the M-protein gene and protein expression in vivo in a dose-dependent manner. Furthermore, the M-protein gene expression was elevated 3.4-fold in hypothyroid rats. Accordingly, T3 was able to rapidly and strongly reduce the M-protein gene expression in neonatal cardiomyocytes. Deletions at the M-protein promoter and bioinformatics approach suggested an area responsive to T3, which was confirmed by chromatin immunoprecipitation assay. Functional assays in cultured neonatal cardiomyocytes revealed that depletion of M-protein (by small interfering RNA) drives a severe decrease in speed of contraction. Interestingly, mRNA and protein levels of other M-band components, myomesin and embryonic-heart myomesin, were not altered by T3. We concluded that the M-protein expression is strongly and rapidly repressed by T3 in cardiomyocytes, which represents an important aspect for the basis of T3-dependent sarcomeric deleterious effects in the heart.