Melanocortin 4 Receptor Activation Attenuates Mitochondrial Dysfunction in Skeletal Muscle of Diabetic Rats.

A previous study has confirmed that the central melanocortin system was able to mediate skeletal muscle AMP-activated protein kinase (AMPK) activation in mice fed a high-fat diet, while activation of the AMPK signaling pathway significantly induced mitochondrial biogenesis. Our hypothesis was that melanocortin 4 receptor (MC4R) was involved in the development of skeletal muscle injury in diabetic rats. In this study, we treated diabetic rats intracerebroventricularly with MC4R agonist R027-3225 or antagonist SHU9119, respectively. Then, we measured the production of reactive oxygen species (ROS), the levels of malondialdehyde (MDA) and glutathione (GSH), the mitochondrial DNA (mtDNA) content and mitochondrial biogenesis, and the protein levels of p-AMPK, AMPK, peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α), sirtuin 1 (SIRT1), and manganese superoxide dismutase (MnSOD) in the skeletal muscle of diabetic rats. The results showed that there was significant skeletal muscle injury in the diabetic rats along with serious oxidative stress and decreased mitochondrial biogenesis. Treatment with R027-3225 reduced oxidative stress and induced mitochondrial biogenesis in skeletal muscle, and also activated the AMPK-SIRT1-PGC-1α signaling pathway. However, diabetic rats injected with MC4R antagonist SHU9119 showed an aggravated oxidative stress and mitochondrial dysfunction in skeletal muscle. In conclusion, our results revealed that MC4R activation was able to attenuate oxidative stress and mitochondrial dysfunction in skeletal muscle induced by diabetes partially through activating the AMPK-SIRT1-PGC-1α signaling pathway. J. Cell. Biochem. 118: 4072-4079, 2017. © 2017 Wiley Periodicals, Inc.

[Clinical analysis and autoimmune regulator gene mutation of autoimmune polyendocrinopathy syndrome type I in a family: a report of one case].

The clinical data of one patient with autoimmune polyendocrinopathy syndrome type I were collected. PCR-DNA direct bidirectional sequencing was applied for mutation screening of 14 exons in autoimmune regulator (AIRE) gene in the patient and her parents. A total of 50 unrelated healthy controls were selected and tested. The bioinformatic methods were used to predict the possible impact of the mutations on the structure and function of the AIRE protein. The results of sequencing showed that heterozygous mutation c.622G>T (p.G208W) in exon 5 of the AIRE gene was detected in the patient and was a novel mutation, which had not been reported in the HGMD database and latest articles. This mutation was not detected in the 50 unrelated normal controls. The novel mutation of c.622G>T (p.G208W) in AIRE gene might play an important role in the pathogenesis of this case of autoimmune polyendocrinopathy syndrome type I.

Analysis of 2 novel mutations of PHEX gene inducing X-linked dominant hypophosphatemia rickets in 2 families: Two case reports.

RATIONALE: X-linked dominant hypophosphatemia rickets (XLH, OMIM 307800) is the most common hereditary hypophosphatemic rickets and characterized by growth retardation, skeletal malformations, dental dysplasia, spontaneous fractures and osteomalacia. PHEX gene was identified for XLH and novel mutations were consistent with loss of function. PATIENT CONCERNS: Case1: the proband 1 III3 in family 1 was a fourteen-year-old boy with bowing of bilateral legs, obviously enlarged joints, tooth absence and difficulty in walking; X-rays showed bilateral femoral multiple fractures with sclerosis at the fracture edge. Case 2: the proband 2 III2, a five-year-old boy in family 2, showed growth retardation, dental dysplasia, gingiva abscess and bilateral legs malformations; X-rays showed low bone density, delayed bone age, bowing of legs, frayed and widened metaphyses of the distal femurs and proximal tibias. Both of their mothers suffered from skeletal malformations, tooth absence and were performed with osteotomy due to fractures of lower limb. Their biochemical parameters showed hypophosphatemia, elevated alkaline phosphatase. DIAGNOSES: X-linked dominant hypophosphatemia rickets (XLH). INTERVENTIONS AND OUTCOMES: Treatment with high doses of phosphate and 1,25-dihydroxyvitamin D3, the height of proband 2 increased 10 cm and femoral Multiple fracture of proband1 almost healed after treatment for 6 months and the patients's PHEX gene was investigated. LESSONS: Two novel pathogenic PHEX mutations were found: c.497delG in family 1 and c.388G> T in family 2, both of which caused early termination of translation and produced truncated protein. Serum FGF23 concentration in our XLH patients were obviously higher than the normal and may be related to age to some extent. Early initiation of treatment produces better effect.

SIRT1 overexpression in skeletal muscle in vivo induces increased insulin sensitivity and enhanced complex I but not complex II-V functions in individual subsarcolemmal and intermyofibrillar mitochondria.

SIRT1 is known to improve insulin resistance (IR), but whether this effect is direct or not is still unclear, and this question has not been addressed in vivo in the skeletal muscle. Therefore, we sought to test if acute overexpression of SIRT1 in skeletal muscle of high-fat diet (HFD) rats in vivo would affect subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondrial complexes I-V activities and antioxidant enzymes thereby improving insulin action. In vivo electrotransfer was used to overexpress SIRT1 in the skeletal muscle of rats fed HFD for 12 weeks. Skeletal muscle insulin sensitivity and downstream effects of SIRT1 on AMPK, SIRT3, and mitochondrial biogenesis were studied. Citrate synthase (CS), complexes I-V, oxidative stress, and antioxidant levels were assessed in SS and IMF mitochondria. HFD rats showed skeletal muscle IR as well as decreased SIRT1 and SIRT3 expressions, mitochondrial DNA (mtDNA), and mitochondrial biogenesis (p < 0.05). SS and IMF mitochondria displayed lower CS, complexes I-V, and antioxidant enzyme activities (p < 0.05). By contrast, moderate (~2.5 folds) SIRT1 overexpression attenuated HFD-induced skeletal muscle IR. This improvement was associated with increased AMPK, PGC-1α, SIRT3, and mtDNA expressions as well as SS and IMF mitochondrial CS and complexes I-V activities. Importantly, SIRT1 overexpression largely restored antioxidant enzyme activities and enhanced complex I but not complexes II-V functions in individual SS and IMF mitochondria. This study suggests that SIRT1 overexpression improved IR at least partly by targeting complex I functions of SS and IMF mitochondria through the activation of SIRT1 and SIRT3.