Role of miR-181c in Diet-induced obesity through regulation of lipid synthesis in liver

We recently identified a nuclear-encoded miRNA (miR-181c) in cardiomyocytes that can translocate into mitochondria to regulate mitochondrial gene mt-COX1 and influence obesity-induced cardiac dysfunction through the mitochondrial pathway. Because liver plays a pivotal role during obesity, we hypothesized that miR-181c might contribute to the pathophysiological complications associated with obesity. Therefore, we used miR-181c/d^-/- mice to study the role of miR-181c in hepatocyte lipogenesis during diet-induced obesity. The mice were fed a high-fat (HF) diet for 26 weeks, during which indirect calorimetric measurements were made. Quantitative PCR (qPCR) was used to examine the expression of genes involved in lipid synthesis. We found that miR-181c/d^-/- mice were not protected against all metabolic consequences of HF exposure. After 26 weeks, the miR-181c/d^-/- mice had a significantly higher body fat percentage than did wild-type (WT) mice. Glucose tolerance tests showed hyperinsulinemia and hyperglycemia, indicative of insulin insensitivity in the miR-181c/d^-/- mice. miR-181c/d^-/- mice fed the HF diet had higher serum and liver triglyceride levels than did WT mice fed the same diet. qPCR data showed that several genes regulated by isocitrate dehydrogenase 1 (IDH1) were more upregulated in miR-181c/d^-/- liver than in WT liver. Furthermore, miR-181c delivered in vivo via adeno-associated virus attenuated the lipogenesis by downregulating these same lipid synthesis genes in the liver. In hepatocytes, miR-181c regulates lipid biosynthesis by targeting IDH1. Taken together, the data indicate that overexpression of miR-181c can be beneficial for various lipid metabolism disorders.

Inhibition of phosphodiesterase type 9 reduces obesity and cardiometabolic syndrome in mice

Central obesity with cardiometabolic syndrome (CMS) is a major global contributor to human disease, and effective therapies are needed. Here, we show that cyclic GMP-selective phosphodiesterase 9A inhibition (PDE9-I) in both male and ovariectomized female mice suppresses preestablished severe diet-induced obesity/CMS with or without superimposed mild cardiac pressure load. PDE9-I reduces total body, inguinal, hepatic, and myocardial fat; stimulates mitochondrial activity in brown and white fat; and improves CMS, without significantly altering activity or food intake. PDE9 localized at mitochondria, and its inhibition in vitro stimulated lipolysis in a PPARα-dependent manner and increased mitochondrial respiration in both adipocytes and myocytes. PPARα upregulation was required to achieve the lipolytic, antiobesity, and metabolic effects of PDE9-I. All these PDE9-I-induced changes were not observed in obese/CMS nonovariectomized females, indicating a strong sexual dimorphism. We found that PPARα chromatin binding was reoriented away from fat metabolism-regulating genes when stimulated in the presence of coactivated estrogen receptor-α, and this may underlie the dimorphism. These findings have translational relevance given that PDE9-I is already being studied in humans for indications including heart failure, and efficacy against obesity/CMS would enhance its therapeutic utility.

PKG oxidation at Cys42 amplifies mTORC1 activation to worsen hypertrophic heart disease

Rationale

Protein kinase G-1a (PKG1a) phosphorylation of tuberous sclerosis complex 2 (TSC2, or tuberin) at serine 1365 (S1365) potently suppresses mTORC1 activation. This results in greater autophagy and limits pathological hypertrophy myocytes and the heart. Cardiac stress also induce oxidation of PKG1a between cysteine 42 residues in homo-monomers, which reduces cardioprotection.

Objective

We tested the hypothesis that pathological mTORC1 activation is potently amplified by concomitant PKG1a C42-oxidation, and that this is countered by stimulating soluble guanylyl cyclase-1 (GC-1).

Methods and results

In mice expressing only C42-redox inhibited PKG1a (PKG1aCS), pressure-overload (PO) induces markedly less mTORC1 activation, increasing autophagic flux and reducing protein aggregation, hypertrophy, and dysfunction compared to PO in PKG1aWT mice. Similar results were obtained in cardiomyocytes exposed to endothelin-1. Protection against PO in PKG1aCS mice was similar to PKG1aWT co-treated with the mTORC1-inhibitor everolimus. TSC2 S1365 phosphorylation increased more in PKG1aCS than PKG1aWT myocardium after PO. Knock-in mice with TSC2 S1365A and PKG1aCS mutations, to prevent TSC2 phosphorylation by PKG1a displayed amplified mTORC1, cardiodepression, and mortality after PO as compared to PKG1aCS. Lastly, the marked disparity between PKG1aWT and PKG1aCS PO phenotype for TSC2 S1365 phosphorylation, mTORC1 activation, and cardiac dysfunction is overcome by BAY-602770, a direct stimulator of GC-1.

Conclusion

Oxidant-induced PKG1a C42 dimerization blunts its attenuation of mTORC1 activity by reducing TSC2 S1365 phosphorylation, thereby contributing to inadequate autophagy and worsened hypertrophic dysfunction. This is ameliorated by direct GC-1 stimulation.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): DFG

CHIP phosphorylation by protein kinase G enhances protein quality control and attenuates cardiac ischemic injury

Proteotoxicity from insufficient clearance of misfolded/damaged proteins underlies many diseases. Carboxyl terminus of Hsc70-interacting protein (CHIP) is an important regulator of proteostasis in many cells, having E3-ligase and chaperone functions and often directing damaged proteins towards proteasome recycling. While enhancing CHIP functionality has broad therapeutic potential, prior efforts have all relied on genetic upregulation. Here we report that CHIP-mediated protein turnover is markedly post-translationally enhanced by direct protein kinase G (PKG) phosphorylation at S20 (mouse, S19 human). This increases CHIP binding affinity to Hsc70, CHIP protein half-life, and consequent clearance of stress-induced ubiquitinated-insoluble proteins. PKG-mediated CHIP-pS20 or expressing CHIP-S20E (phosphomimetic) reduces ischemic proteo- and cytotoxicity, whereas a phospho-silenced CHIP-S20A amplifies both. In vivo, depressing PKG activity lowers CHIP-S20 phosphorylation and protein, exacerbating proteotoxicity and heart dysfunction after ischemic injury. CHIP-S20E knock-in mice better clear ubiquitinated proteins and are cardio-protected. PKG activation provides post-translational enhancement of protein quality control via CHIP.

Exosomal MicroRNA-15a Transfer from the Pancreas Augments Diabetic Complications by Inducing Oxidative Stress

AIMS

MicroRNAs (miRNAs), one type of noncoding RNA, modulate post-transcriptional gene expression in various pathogenic pathways in type 2 diabetes (T2D). Currently, little is known about how miRNAs influence disease pathogenesis by targeting cells at a distance. The purpose of this study was to investigate the role of exosomal miRNAs during T2D.

RESULTS

We show that miR-15a is increased in the plasma of diabetic patients, correlating with disease severity. miR-15 plays an important role in insulin production in pancreatic β-cells. By culturing rat pancreatic β-cells (INS-1) cells in high-glucose media, we identified a source of increased miR-15a in the blood as exosomes secreted by pancreatic β-cells. We postulate that miR-15a, produced in pancreatic β-cells, can enter the bloodstream and contribute to retinal injury. miR-15a overexpression in Müller cells can be induced by exposing Müller cells to exosomes derived from INS-1 cells under high-glucose conditions and results in oxidative stress by targeting Akt3, which leads to apoptotic cell death. The in vivo relevance of these findings is supported by results from high-fat diet and pancreatic β-cell-specific miR-15a^-/- mice.

INNOVATION

This study highlights an important and underappreciated mechanism of remote cell-cell communication (exosomal transfer of miRNA) and its influence on the development of T2D complications.

CONCLUSION

Our findings suggest that circulating miR-15a contributes to the pathogenesis of diabetes and supports the concept that miRNAs released by one cell type can travel through the circulation and play a role in disease progression via their transfer to different cell types, inducing oxidative stress and cell injury. Antioxid. Redox Signal. 27, 913-930.

Divergent Effects of miR-181 Family Members on Myocardial Function Through Protective Cytosolic and Detrimental Mitochondrial microRNA Targets

Background

MicroRNA (miRNA) is a type of noncoding RNA that can repress the expression of target genes through posttranscriptional regulation. In addition to numerous physiologic roles for miRNAs, they play an important role in pathophysiologic processes affecting cardiovascular health. Previously, we reported that nuclear encoded microRNA (miR‐181c) is present in heart mitochondria, and importantly, its overexpression affects mitochondrial function by regulating mitochondrial gene expression.

Methods and Results

To investigate further how the miR‐181 family affects the heart, we suppressed miR‐181 using a miR‐181‐sponge containing 10 repeated complementary miR‐181 “seed” sequences and generated a set of H9c2 cells, a cell line derived from rat myoblast, by stably expressing either a scrambled or miR‐181‐sponge sequence. Sponge‐H9c2 cells showed a decrease in reactive oxygen species production and reduced basal mitochondrial respiration and protection against doxorubicin‐induced oxidative stress. We also found that miR‐181a/b targets phosphatase and tensin homolog (PTEN), and the sponge‐expressing stable cells had increased PTEN activity and decreased PI3K signaling. In addition, we have used miR‐181a/b^−/− and miR‐181c/d^−/− knockout mice and subjected them to ischemia‐reperfusion injury. Our results suggest divergent effects of different miR‐181 family members: miR‐181a/b targets PTEN in the cytosol, resulting in an increase in infarct size in miR‐181a/b^−/− mice due to increased PTEN signaling, whereas miR‐181c targets mt‐COX1 in the mitochondria, resulting in decreased infarct size in miR‐181c/d^−/− mice.

Conclusions

The miR‐181 family alters the myocardial response to oxidative stress, notably with detrimental effects by targeting mt‐COX1 (miR‐181c) or with protection by targeting PTEN (miR‐181a/b).