Jaetaek Kim

Insulin-like growth factor I receptor signaling is required for exercise-induced cardiac hypertrophy.

The receptors for IGF-I (IGF-IR) and insulin (IR) have been implicated in physiological cardiac growth, but it is unknown whether IGF-IR or IR signaling are critically required. We generated mice with cardiomyocyte-specific knockout of IGF-IR (CIGF1RKO) and compared them with cardiomyocyte-specific insulin receptor knockout (CIRKO) mice in response to 5 wk exercise swim training. Cardiac development was normal in CIGF1RKO mice, but the hypertrophic response to exercise was prevented. In contrast, despite reduced baseline heart size, the hypertrophic response of CIRKO hearts to exercise was preserved. Exercise increased IGF-IR content in control and CIRKO hearts. Akt phosphorylation increased in exercise-trained control and CIRKO hearts and, surprisingly, in CIGF1RKO hearts as well. In exercise-trained control and CIRKO mice, expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) and glycogen content were both increased but were unchanged in trained CIGF1RKO mice. Activation of AMP-activated protein kinase (AMPK) and its downstream target eukaryotic elongation factor-2 was increased in exercise-trained CIGF1RKO but not in CIRKO or control hearts. In cultured neonatal rat cardiomyocytes, activation of AMPK with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) prevented IGF-I/insulin-induced cardiomyocyte hypertrophy. These studies identify an essential role for IGF-IR in mediating physiological cardiomyocyte hypertrophy. IGF-IR deficiency promotes energetic stress in response to exercise, thereby activating AMPK, which leads to phosphorylation of eukaryotic elongation factor-2. These signaling events antagonize Akt signaling, which although necessary for mediating physiological cardiac hypertrophy, is insufficient to promote cardiac hypertrophy in the absence of myocardial IGF-I signaling.

Mechanisms for increased myocardial fatty acid utilization following short-term high-fat feeding

AIMS Diet-induced obesity is associated with increased myocardial fatty acid (FA) utilization, insulin resistance, and cardiac dysfunction. The study was designed to test the hypothesis that impaired glucose utilization accounts for initial changes in FA metabolism. METHODS AND RESULTS Ten-week-old C57BL6J mice were fed a high-fat diet (HFD, 45% calories from fat) or normal chow (4% calories from fat). Cardiac function and substrate metabolism in isolated working hearts, glucose uptake in isolated cardiomyocytes, mitochondrial function, insulin-stimulated protein kinase B (Akt/PKB) and Akt substrate (AS-160) phosphorylation, glucose transporter 4 (GLUT4) translocation, pyruvate dehydrogenase (PDH) activity, and mRNA levels for metabolic genes were determined after 2 or 5 weeks of HFD. Two weeks of HFD reduced basal rates of glycolysis and glucose oxidation and prevented insulin stimulation of glycolysis in hearts and reduced insulin-stimulated glucose uptake in cardiomyocytes. Insulin-stimulated Akt/PKB and AS-160 phosphorylation were preserved, and PDH activity was unchanged. GLUT4 content was reduced by 55% and GLUT4 translocation was significantly attenuated. HFD increased FA oxidation rates and myocardial oxygen consumption (MVO2), which could not be accounted for by mitochondrial uncoupling or by increased expression of peroxisome proliferator activated receptor-alpha (PPAR-alpha) target genes, which increased only after 5 weeks of HFD. CONCLUSION Rates of myocardial glucose utilization are altered early in the course of HFD because of reduced GLUT4 content and GLUT4 translocation despite normal insulin signalling to Akt/PKB and AS-160. The reciprocal increase in FA utilization is not due to PPAR-alpha-mediated signalling or mitochondrial uncoupling. Thus, the initial increase in myocardial FA utilization in response to HFD likely results from impaired glucose transport that precedes impaired insulin signalling.

Methylglyoxal Induces Apoptosis Mediated by Reactive Oxygen Species in Bovine Retinal Pericytes

One of the histopathologic hallmarks of early diabetic retinopathy is the loss of pericytes. Evidences suggest that the pericyte loss in vivo is mediated by apoptosis. However, the underlying cause of pericyte apoptosis is not fully understood. This study investigated the influence of methylglyoxal (MGO), a reactive α-dicarbonyl compound of glucose metabolism, on apoptotic cell death in bovine retinal pericytes. Analysis of internucleosomal DNA fragmentation by ELISA showed that MGO (200 to 800 µM) induced apoptosis in a concentration-dependent manner. Intracellular reactive oxygen species were generated earlier and the antioxidant, N-acetyl cysteine, inhibited the MGO-induced apoptosis. NF-κB activation and increased caspase-3 activity were detected. Apoptosis was also inhibited by the caspase-3 inhibitor, Z-DEVD-fmk, or the NF-κB inhibitor, pyrrolidine dithiocarbamate. These data suggest that elevated MGO levels observed in diabetes may cause apoptosis in bovine retinal pericytes through an oxidative stress mechanism and suggests that the nuclear activation of NF-κB are involved in the apoptotic process.

Receptor activator of nuclear factor-κB ligand is a novel inducer of myocardial inflammation

AIMS Although increased levels of myocardial receptor activator of nuclear factor (NF)-κB ligand (RANKL) have been reported in heart failure, the role of this pathway in mediating activation of inflammatory pathways during myocardial remodelling is less well understood. This study sought to determine the role of myocardial RANKL in regulating cytokine expression. METHODS AND RESULTS A marked increase in RANKL expression occurred as early as 6h following transverse aortic constriction (TAC) in mouse hearts and persisted at 3 and 17 days. An increase in tumour necrosis factor-α (TNF-α), interleukin (IL)-1α, and IL-1β was observed in the hypertrophied hearts only at 3 or 17 days after TAC. Treatment with losartan significantly attenuated TAC-induced cardiac hypertrophy, in parallel with decreased expression of RANKL, TNF-α, IL-1α, and IL-1β. Furthermore, injection of a RANKL-neutralizing monoclonal antibody attenuated RANKL-induced cytokine expression. RANKL stimulated expression of TNF-α, IL-1α, and IL-1β in neonatal rat cardiomyocytes via activation of NF-κB. RANKL-induced NF-κB activation and expression of these cytokines were both attenuated when RANK, receptor for RANKL, or TRAF2 or TRAF6, adaptors for RANK, was silenced by siRNA. Furthermore, inhibitors of phospholipase C (PLC), protein kinase C (PKC), and inhibitor of κB kinase also significantly inhibited RANKL-induced cellular activities, but inhibitors of phosphatidylinositol 3-kinase, extracellular signal-regulated kinase, or p38 mitogen-activated protein kinase were without effect. CONCLUSION Our data demonstrate for the first time that the pressure-overloaded myocardium generates RANKL, which induces TNF-α, IL-1α, and IL-1β production via a RANK-TRAF2/TRAF6-PLC-PKC-NF-κB-mediated autocrine mechanism.

Mechanisms and Consequences of Inflammatory Signaling in the Myocardium

To further understand chronic heart disease, such as heart failure and cardiomyopathy, we must fully define signaling pathways within the myocardium. Recent studies suggest that some forms of heart disease are associated with a chronic low-grade inflammation that promotes adverse ventricular remodeling and correlates with disease progression. Several inflammatory mediators, including TNF-α, IL-1β, and IL-6, are involved in cardiac injury subsequent to myocardial ischemia and reperfusion, sepsis, viral myocarditis, and transplant rejection. Once activated, components of the inflammatory response can have both beneficial and deleterious effects on the heart. In this review, we discuss the complex inflammatory signaling pathways in the myocardium and potential therapeutic implications.

Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions.

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear family of ligand activated transcriptional factors and comprise three different isoforms, PPAR-α, PPAR-β/δ, and PPAR-γ. The main role of PPARs is to regulate the expression of genes involved in lipid and glucose metabolism. Several studies have demonstrated that PPAR agonists improve dyslipidemia and glucose control in animals, supporting their potential as a promising therapeutic option to treat diabetes and dyslipidemia. However, substantial differences exist in the therapeutic or adverse effects of specific drug candidates, and clinical studies have yielded inconsistent data on their cardioprotective effects. This review summarizes the current knowledge regarding the molecular function of PPARs and the mechanisms of the PPAR regulation by posttranslational modification in the heart. We also describe the results and lessons learned from important clinical trials on PPAR agonists and discuss the potential future directions for this class of drugs.

IGF-1 receptor deficiency in thyrocytes impairs thyroid hormone secretion and completely inhibits TSH-stimulated goiter

Although thyroid‐stimulating hormone (TSH) is known to be a major regulator of thyroid hormone biosynthesis and thyroid growth, insulin‐like growth factor 1 (IGF‐1) is required for mediating thyrocyte growth in concert with TSH in vitro. We generated mice with thyrocyte‐selective ablation of IGF‐1 receptor (TIGF1RKO) to explore the role of IGF‐1 receptor signaling on thyroid function and growth. In 5‐wk‐old TIGF1RKO mice, serum thyroxine (T4) concentrations were decreased by 30% in concert with a 43% down‐regulation of the monocarboxylate transporter 8 (MCT8), which is involved in T4 secretion. Despite a 3.5‐fold increase in circulating concentrations of TSH, thyroid architecture and size were normal. Furthermore, thyrocyte area was increased by 40% in WT thyroids after 10 d TSH injection, but this effect was absent in TSH‐injected TIGF1RKO mice. WT mice treated with methimazole and sodium perchlorate for 2 or 6 wk exhibited pronounced goiter development (2.0 and 5.4‐fold, respectively), but in TIGF1RKO mice, goiter development was completely abrogated. These data reveal an essential role for IGF‐1 receptor signaling in the regulation of thyroid function and TSH‐stimulated goitrogenesis.—Ock, S., Ahn, J., Lee, S. H., Kang, H., Offermanns, S., Ahn, H. Y., Jo, Y.S., Shong, M., Cho, B. Y., Jo, D., Abel, E. D., Lee, T. J., Park, W. J., Lee, I.‐K., Kim, J. IGF‐1 receptor deficiency in thyrocytes impairs thyroid hormone secretion and completely inhibits TSH‐stimulated goiter. FASEB J. 27, 4899–4908 (2013). www.fasebj.org

PICOT increases cardiac contractility by inhibiting PKCζ activity

Protein kinase C (PKC)-interacting cousin of thioredoxin (PICOT) has distinct anti-hypertrophic and inotropic functions. We have previously shown that PICOT exerts its anti-hypertrophic effect by inhibiting calcineurin-NFAT signaling through its C-terminal glutaredoxin domain. However, the mechanism underlying the inotropic effect of PICOT is unknown. The results of protein pull-down experiments showed that PICOT directly binds to the catalytic domain of PKCζ through its N-terminal thioredoxin-like domain. Purified PICOT protein inhibited the kinase activity of PKCζ in vitro, which indicated that PICOT is an endogenous inhibitor of PKCζ. The inhibition of PKCζ activity with a PKCζ-specific pseudosubstrate peptide inhibitor was sufficient to increase the cardiac contractility in vitro and ex vivo. Overexpression of PICOT or inhibition of PKCζ activity down-regulated PKCα activity, which led to the elevation of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) 2a activity, concomitant with the increased phosphorylation of phospholamban (PLB). Overexpression of PICOT or inhibition of PKCζ activity also down-regulated protein phosphatase (PP) 2A activity, which subsequently resulted in the increased phosphorylation of troponin (Tn) I and T, key myofilament proteins associated with the regulation of contractility. PICOT appeared to inhibit PP2A activity through the disruption of the functional PKCζ/PP2A complex. In contrast to the overexpression of PICOT or inhibition of PKCζ, reduced PICOT expression resulted in up-regulation of PKCα and PP2A activities, followed by decreased phosphorylation of PLB, and TnI and T, respectively, supporting the physiological relevance of these events. Transgene- or adeno-associated virus (AAV)-mediated overexpression of PICOT restored the impaired contractility and prevented further morphological and functional deterioration of the failing hearts. Taken together, the results of the present study suggest that PICOT exerts its inotropic effect by negatively regulating PKCα and PP2A activities through the inhibition of PKCζ activity. This finding provides a novel insight into the regulation of cardiac contractility.

Deletion of IGF-1 Receptors in Cardiomyocytes Attenuates Cardiac Aging in Male Mice

IGF-1 receptor (IGF-1R) signaling is implicated in cardiac hypertrophy and longevity. However, the role of IGF-1R in age-related cardiac remodeling is only partially understood. We therefore sought to determine whether the deletion of the IGF-1R in cardiomyocytes might delay the development of aging-associated myocardial pathologies by examining 2-year-old male cardiomyocyte-specific IGF-1R knockout (CIGF1RKO) mice. Aging was associated with the induction of IGF-1R expression in hearts. Cardiomyocytes hypertrophied with age in wild-type (WT) mice. In contrast, the cardiac hypertrophic response associated with aging was blunted in CIGF1RKO mice. Concomitantly, fibrosis was reduced in aged CIGF1RKO compared with aged WT hearts. Expression of proinflammatory cytokines such as IL-1α, IL-1β, IL-6, and receptor activator of nuclear factor-κB ligand was increased in aged WT hearts, but this increase was attenuated in aged CIGF1RKO hearts. Phosphorylation of Akt was increased in aged WT, but not in aged CIGF1RKO, hearts. In cultured cardiomyocytes, IGF-1 induced senescence as demonstrated by increased senescence-associated β-galactosidase staining, and a phosphoinositide 3-kinase inhibitor inhibited this effect. Furthermore, inhibition of phosphoinositide 3-kinase significantly prevented the increase in IL-1α, IL-1β, receptor activator of nuclear factor-κB ligand, and p21 protein expression by IGF-1. These data reveal an essential role for the IGF-1-IGF-1R-Akt pathway in mediating cardiomyocyte senescence.

Preparation of doxorubicin-containing chitosan microspheres for transcatheter arterial chemoembolization of hepatocellular carcinoma

A new form of doxorubicin hydrochloride (DRH)-containing chitosan microspheres (CMs) was prepared by employing an expanding-loading-shrinking (E-L-S) process. One hundred mg of pre-formed CMs were soaked in absolute ethanol and then placed in reduced pressure (the expanding process). Ten mg of DRH (2 mg ml−1) were added into the expanded CMs (the loading process). Next the microspheres were freeze-dried (the shrinking process). As a result of this E-L-S process, 10% (w/w) DRH-containing CMs (DRH-CM) were made. During 7 days, 22.6% of the DRH was observed to be released on the in vitro drug release study. In addition, these new DRH-CMs could be used for transcatheter arterial chemoembolization (TACE) procedure in VX2 hepatic tumour models of rabbit and the anti-tumour effects of DRH-CMs were investigated. On the post-CT scan 7 days after the TACE, total infarctions of the VX2 tumour were observed in 5 rabbits among the 6 total rabbits.