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Articles by M Leitges
Total Records ( 5 ) for M Leitges
  T. E Jensen , S. J Maarbjerg , A. J Rose , M Leitges and E. A. Richter

Conventional (c) protein kinase C (PKC) activity has been shown to increase with skeletal muscle contraction, and numerous studies using primarily pharmacological inhibitors have implicated cPKCs in contraction-stimulated glucose uptake. Here, to confirm that cPKC activity is required for contraction-stimulated glucose uptake in mouse muscles, contraction-stimulated glucose uptake ex vivo was first evaluated in the presence of three commonly used cPKC inhibitors (calphostin C, Gö-6976, and Gö-6983) in incubated mouse soleus and extensor digitorum longus (EDL) muscles. All potently inhibited contraction-stimulated glucose uptake by 50–100%, whereas both Gö compounds, but not calphostin C, inhibited insulin-stimulated glucose uptake modestly. AMP-activated protein kinase (AMPK) and eukaryotic elongation factor 2 phosphorylation was unaffected by the blockers. PKC was estimated to account for ~97% of total cPKC protein expression in skeletal muscle. However, in muscles from PKC knockout (KO) mice, neither contraction- nor phorbol ester-stimulated glucose uptake ex vivo differed compared with the wild type. Furthermore, the effects of calphostin C and Gö-6983 on contraction-induced glucose uptake were similar in muscles lacking PKC and in the wild type. It can be concluded that PKC, representing ~97% of cPKC in skeletal muscle, is not required for contraction-stimulated glucose uptake. Thus the effect of the PKC blockers on glucose uptake is either nonspecific working on other parts of contraction-induced signaling or the remaining cPKC isoforms are sufficient for stimulating glucose uptake during contractions.

  M. P Sajan , G Bandyopadhyay , A Miura , M. L Standaert , S Nimal , S. L Longnus , E Van Obberghen , I Hainault , F Foufelle , R Kahn , U Braun , M Leitges and R. V. Farese

Activators of 5'-AMP-activated protein kinase (AMPK) 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), metformin, and exercise activate atypical protein kinase C (aPKC) and ERK and stimulate glucose transport in muscle by uncertain mechanisms. Here, in cultured L6 myotubes: AICAR- and metformin-induced activation of AMPK was required for activation of aPKC and ERK; aPKC activation involved and required phosphoinositide-dependent kinase 1 (PDK1) phosphorylation of Thr410-PKC-; aPKC Thr410 phosphorylation and activation also required MEK1-dependent ERK; and glucose transport effects of AICAR and metformin were inhibited by expression of dominant-negative AMPK, kinase-inactive PDK1, MEK1 inhibitors, kinase-inactive PKC-, and RNA interference (RNAi)-mediated knockdown of PKC-. In mice, muscle-specific aPKC (PKC-) depletion by conditional gene targeting impaired AICAR-stimulated glucose disposal and stimulatory effects of both AICAR and metformin on 2-deoxyglucose/glucose uptake in muscle in vivo and AICAR stimulation of 2-[3H]deoxyglucose uptake in isolated extensor digitorum longus muscle; however, AMPK activation was unimpaired. In marked contrast to AICAR and metformin, treadmill exercise-induced stimulation of 2-deoxyglucose/glucose uptake was not inhibited in aPKC-knockout mice. Finally, in intact rodents, AICAR and metformin activated aPKC in muscle, but not in liver, despite activating AMPK in both tissues. The findings demonstrate that in muscle AICAR and metformin activate aPKC via sequential activation of AMPK, ERK, and PDK1 and the AMPK/ERK/PDK1/aPKC pathway is required for metformin- and AICAR-stimulated increases in glucose transport. On the other hand, although aPKC is activated by treadmill exercise, this activation is not required for exercise-induced increases in glucose transport, and therefore may be a redundant mechanism.

  Q Liu , X Chen , S. M MacDonnell , E. G Kranias , J. N Lorenz , M Leitges , S. R Houser and J. D. Molkentin

Protein kinase (PK)C, PKCβ, and PKC comprise the conventional PKC isoform subfamily, which is thought to regulate cardiac disease responsiveness. Indeed, mice lacking the gene for PKC show enhanced cardiac contractility and reduced susceptibility to heart failure. Recent data also suggest that inhibition of conventional PKC isoforms with Ro-32-0432 or Ro-31-8220 enhances heart function and antagonizes failure, although the isoform responsible for these effects is unknown. Here, we investigated mice lacking PKC, PKCβ, and PKC for effects on cardiac contractility and heart failure susceptibility. PKC–/– mice, but not PKCβ–/– mice, showed increased cardiac contractility, myocyte cellular contractility, Ca2+ transients, and sarcoplasmic reticulum Ca2+ load. PKC–/– mice were less susceptible to heart failure following long-term pressure-overload stimulation or 4 weeks after myocardial infarction injury, whereas PKCβ–/– mice showed more severe failure. Infusion of ruboxistaurin (LY333531), an orally available PKC/β/ inhibitor, increased cardiac contractility in wild-type and PKCβ–/– mice, but not in PKC–/– mice. More importantly, ruboxistaurin prevented death in wild-type mice throughout 10 weeks of pressure-overload stimulation, reduced ventricular dilation, enhanced ventricular performance, reduced fibrosis, and reduced pulmonary edema comparable to or better than metoprolol treatment. Ruboxistaurin was also administered to PKCβ–/– mice subjected to pressure overload, resulting in less death and heart failure, implicating PKC as the primary target of this drug in mitigating heart disease. As an aside, PKCβ triple-null mice showed no defect in cardiac hypertrophy following pressure-overload stimulation. In conclusion, PKC functions distinctly from PKCβ and PKC in regulating cardiac contractility and heart failure, and broad-acting PKC inhibitors such as ruboxistaurin could represent a novel therapeutic approach in treating human heart failure.

  M. P Sajan , M. L Standaert , S Nimal , U Varanasi , T Pastoor , S Mastorides , U Braun , M Leitges and R. V. Farese

Obesity is frequently associated with systemic insulin resistance, glucose intolerance, and hyperlipidemia. Impaired insulin action in muscle and paradoxical diet/insulin-dependent overproduction of hepatic lipids are important components of obesity, but their pathogenesis and inter-relationships between muscle and liver are uncertain. We studied two murine obesity models, moderate high-fat-feeding and heterozygous muscle-specific PKC- knockout, in both of which insulin activation of atypical protein kinase C (aPKC) is impaired in muscle, but conserved in liver. In both models, activation of hepatic sterol receptor element binding protein-1c (SREBP-1c) and NFB (nuclear factor-kappa B), major regulators of hepatic lipid synthesis and systemic insulin resistance, was chronically increased in the fed state. In support of a critical mediatory role of aPKC, in both models, inhibition of hepatic aPKC by adenovirally mediated expression of kinase-inactive aPKC markedly diminished diet/insulin-dependent activation of hepatic SREBP-1c and NFB, and concomitantly improved hepatosteatosis, hypertriglyceridemia, hyperinsulinemia, and hyperglycemia. Moreover, in high-fat–fed mice, impaired insulin signaling to IRS-1–dependent phosphatidylinositol 3-kinase, PKB/Akt and aPKC in muscle and hyperinsulinemia were largely reversed. In obesity, conserved hepatic aPKC-dependent activation of SREBP-1c and NFB contributes importantly to the development of hepatic lipogenesis, hyperlipidemia, and systemic insulin resistance. Accordingly, hepatic aPKC is a potential target for treating obesity-associated abnormalities.

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