ABSTRACT
Understanding the molecular mechanisms of skeletal muscle regeneration is crucial to exploiting this pathway for use in tissue repair. Our data demonstrate that the MEF2A transcription factor plays an essential role in skeletal muscle regeneration in adult mice. Injured Mef2a knockout mice display widespread necrosis and impaired myofiber formation. MEF2A controls this process through its direct regulation of the largest known mammalian microRNA (miRNA) cluster, the Gtl2-Dio3 locus. A subset of the Gtl2-Dio3 miRNAs represses secreted Frizzled-related proteins (sFRPs), inhibitors of WNT signaling. Consistent with these data, Gtl2-Dio3-encoded miRNAs are downregulated in regenerating Mef2a knockout muscle, resulting in upregulated sFRP expression and attenuated WNT activity. Furthermore, myogenic differentiation in Mef2a-deficient myoblasts is rescued by overexpression of miR-410 and miR-433, two miRNAs in the Gtl2-Dio3 locus that repress sFRP2, or by treatment with recombinant WNT3A and WNT5A. Thus, miRNA-mediated modulation of WNT signaling by MEF2A is a requisite step for proper muscle regeneration, and represents an attractive pathway for enhancing regeneration of diseased muscle.
Subject(s)
Carbocyanines/metabolism , MicroRNAs/metabolism , Muscle, Skeletal/physiology , Myogenic Regulatory Factors/physiology , RNA, Long Noncoding/genetics , RNA, Long Noncoding/metabolism , Regeneration/physiology , Wnt Proteins/metabolism , Animals , COS Cells , Cell Line , Cells, Cultured , Chlorocebus aethiops , Frizzled Receptors/genetics , Gene Knockdown Techniques , Humans , MEF2 Transcription Factors , Mice , Mice, Knockout , Myogenic Regulatory Factors/genetics , Signal Transduction/physiology , Up-Regulation/genetics , Wnt Proteins/physiologyABSTRACT
OBJECTIVE: Diabetes leads to protein kinase C (PKC)-beta overactivation and microvascular dysfunction, possibly resulting in disordered skin microvascular blood flow (SkBF) and other changes observed in diabetic peripheral neuropathy (DPN) patients. We investigate the effects of the isoform-selective PKC-beta inhibitor ruboxistaurin mesylate on neurovascular function and other measures of DPN. RESEARCH DESIGN AND METHODS: Endothelium-dependent and C fiber-mediated SkBF, sensory symptoms, neurological deficits, nerve fiber morphometry, quantitative sensory and autonomic function testing, nerve conduction studies, quality of life (using the Norfolk Quality-of-Life Questionnaire for Diabetic Neuropathy [QOL-DN]), and adverse events were evaluated for 20 placebo- and 20 ruboxistaurin-treated (32 mg/day) DPN patients (aged > or =18 years; with type 1 or type 2 diabetes and A1C < or =11%) during a randomized, double-masked, single-site, 6-month study. RESULTS: Endothelium-dependent (+78.2%, P < 0.03) and C fiber-mediated (+56.4%, P < 0.03) SkBF at the distal calf increased from baseline to end point. Significant improvements from baseline within the ruboxistaurin group were also observed for the Neuropathy Total Symptom Score-6 (NTSS-6) (3 months -48.3%, P = 0.01; end point -66.0%, P < 0.0006) and the Norfolk QOL-DN symptom subscore and total score (end point -41.2%, P = 0.01, and -41.0, P = 0.04, respectively). Between-group differences in baseline-to-end point change were observed for NTSS-6 total score (placebo -13.1%; ruboxistaurin -66.0%, P < 0.03) and the Norfolk QOL-DN symptom subscore (placebo -4.0%; ruboxistaurin -41.2%, P = 0.041). No significant ruboxistaurin effects were demonstrated for the remaining efficacy measures. Adverse events were consistent with those observed in previous ruboxistaurin studies. CONCLUSIONS: In this cohort of DPN patients, ruboxistaurin enhanced SkBF at the distal calf, reduced sensory symptoms (NTSS-6), improved measures of Norfolk QOL-DN, and was well tolerated.
Subject(s)
Diabetic Neuropathies/drug therapy , Enzyme Inhibitors/therapeutic use , Indoles/therapeutic use , Maleimides/therapeutic use , Microcirculation/physiology , Protein Kinase C/antagonists & inhibitors , Regional Blood Flow/drug effects , Skin/blood supply , Aged , Blood Flow Velocity , Diabetes Mellitus, Type 1/complications , Diabetes Mellitus, Type 2/complications , Diabetic Neuropathies/diagnosis , Female , Humans , Male , Microcirculation/drug effects , Middle Aged , Placebos , Protein Kinase C beta , Racial GroupsABSTRACT
A 57-year-old Caucasian man presented with diaphragmatic paralysis and type 2 diabetes. He had severe orthopnea that remained unchanged for 1 year. He was later diagnosed with distal symmetric polyneuropathy and was started on topiramate. Within 26 weeks of treatment, the patient showed improvement in diaphragmatic function and regrowth of intraepidermal nerve fibers, accompanied by improvement in respiratory and peripheral neuropathy symptoms. Topiramate may prove to be an effective agent in the treatment of nonremitting diaphragmatic paralysis and regrowth of intraepidermal nerve fibers.
