glycogen and Vitamin-D-Deficiency

Vitamin D deficiency leads to pathologies of multiple organ systems including skeletal muscle. Patients with severe vitamin D deficiency exhibit muscle weakness and are susceptible to frequent falls. Mice lacking a functional vitamin D receptor (VDR) develop severe skeletal muscle atrophy immediately after weaning. But the root cause of myopathies when vitamin D signalling is impaired is unknown. Because vitamin D deficiency leads to metabolic changes as well, we hypothesized that the skeletal muscle atrophy in mice lacking VDR may have a metabolic origin.. We analysed wild-type (WT) mice as well as vitamin D receptor null (vdr-/-) mice for skeletal muscle proteostasis, energy metabolism, systemic glucose homeostasis, and muscle glycogen levels. Dysregulation of signalling pathways as well as the glycogen synthesis and utilization machinery were also analysed using western blots. qRT-PCR assays were performed to understand changes in mRNA levels.. Skeletal muscles of vdr-/- exhibited higher expression levels of muscle-specific E3 ubiquitin ligases and showed increased protein ubiquitination, suggesting up-regulation of protein degradation. Foxo1 transcription factor was activated in vdr-/- while Foxo3 factor was unaffected. Fasting protein synthesis as well as mTORC1 pathways were severely down-regulated in vdr-/- mice. Skeletal muscle ATP levels were low in vdr-/- (0.58 ± 0.18 μmol/mL vs. 1.6 ± 0.0.14 μmol/mL, P = 0.006), leading to increased AMPK activity. Muscle energy deprivation was not caused by decreased mitochondrial activity as we found the respiratory complex II activity in vdr-/- muscles to be higher compared with WT (0.29 ± 0.007 mU/μL vs. 0.16 ± 0.005 mU/μL). vdr-/- mice had lower fasting blood glucose levels (95 ± 14.5 mg/dL vs. 148.6 ± 6.1 mg/dL, P = 0.0017) while they exhibited hyperlactataemia (7.42 ± 0.31 nmol/μL vs. 4.95 ± 0.44 nmol/μL, P = 0.0032), suggesting systemic energy deficiency in these mice. Insulin levels in these mice were significantly lower in response to intraperitoneal glucose injection (0.69 ± 0.08 pg/mL vs. 1.11 ± 0.09 pg/mL, P = 0.024). Skeletal muscles of these mice exhibit glycogen storage disorder characterized by increased glycogen accumulation. The glycogen storage disorder in vdr-/- muscles is driven by increased glycogen synthase activity and decreased glycogen phosphorylase activity. Increased glycogenin expression supports higher levels of glycogen synthesis in these muscles.. The results presented show that lack of vitamin D signalling leads to a glycogen storage defect in the skeletal muscles, which leads to muscle energy deprivation. The inability of vdr-/- skeletal muscles to use glycogen leads to systemic defects in glucose homeostasis, which in turn leads to proteostasis defects in skeletal muscles and atrophy.

Topics: Animals; Glycogen; Humans; Mice; Muscle, Skeletal; Muscular Diseases; Receptors, Calcitriol; Vitamin D Deficiency

Pandemic vitamin D deficiency is associated with insulin resistance and type 2 diabetes. Vitamin D supplementation has been reported to have improved glucose homeostasis. However, its mechanism to improve insulin sensitivity remains unclear.. Male C57BL/6J mice are fed with/without vitamin D control (CD) or Western (WD) diets for 15 weeks. The vitamin-D-deficient lean (CDVDD) and obese (WDVDD) mice are further subdivided into two groups. One group is re-supplemented with vitamin D for 6 weeks and hepatic insulin signaling is examined. Both CD and WD mice with vitamin D deficiency developed insulin resistance. Vitamin D supplementation in CDVDD mice significantly improved insulin sensitivity, hepatic inflammation, and antioxidative capacity. The hepatic insulin signals like pAKT, pFOXO1, and pGSK3β are increased and the downstream Pepck, G6pase, and Pgc1α are reduced. Furthermore, the lipogenic genes Srebp1c, Acc, and Fasn are decreased, indicating that hepatic lipid accumulation is inhibited.. The results demonstrate that vitamin D deficiency induces insulin resistance. Its supplementation has significant beneficial effects on pathophysiological mechanisms in type 2 diabetes but only in lean and not in the obese phenotype. The increased subacute inflammation and insulin resistance in obesity cannot be significantly alleviated by vitamin D supplementation. This needs to be taken into consideration in the design of new clinical trials.

Topics: Animals; Body Weight; Diet, High-Fat; Forkhead Box Protein O1; Gluconeogenesis; Glucose; Glycogen; Hepatitis; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Obesity; Oxidative Stress; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Vitamin D; Vitamin D Deficiency

Information regarding the presence of the glyoxylate cycle in chick liver was sought. This metabolic pathway has long been thought to be absent from vertebrate tissues. Previous studies in other tissues have shown that, when present, this pathway is sensitive to vitamin-D. Thus, the effect of long-term vitamin-D deficiency and subsequent vitamin-D replacement on liver structure was studied by light microscopy. In addition, specific biochemical assays for the presence of glyoxylate cycle enzymes were performed. Light microscopy of lipid extracted tissues, light microscopic histochemistry, and quantitative histochemistry showed that the hepatocytes from vitamin-D-deficient animals contained primarily lipid. Hepatocytes from normal and vitamin-D-replete livers contained primarily carbohydrate as judged by their staining with periodic acid-Schiff (PAS). Also, malate synthase positive peroxisomes were seen in hepatocytes from normal and vitamin-D-treated chicks. Structures positive for this glyoxylate cycle enzyme were rarely seen in the hepatocytes from vitamin-D-deficient animals. Biochemical analyses showed the presence of the two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, in chick hepatocytes. The activity of these enzymes was markedly increased in the vitamin-D-replete livers. In addition, chick hepatocytes demonstrated the capacity to oxidize fatty acid in the presence of cyanide. This activity, which is characteristic of peroxisomal B-oxidation rather than mitochondrial, was stimulated by vitamin-D treatment. Lastly, incubation of chick liver in the presence of a fatty acid substrate (palmitate) led to higher tissue glycogen content. The latter was further increased in liver from vitamin-D-replete animals. These data show the presence of glyoxylate cycle enzymes in a higher vertebrate and indicate that this tissue is endowed with the capacity to convert lipid to carbohydrate.

Topics: Animals; Animals, Newborn; Calcium; Chickens; Cholecalciferol; Cyanides; Fatty Acids; Glycogen; Glyoxylates; Histocytochemistry; Liver; Oxidation-Reduction; Vitamin D Deficiency

Evidence for the glyoxylate cycle in the mammalian rat liver was sought. Activity of two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, was found in rat liver homogenates. Vitamin D3 treatment of rachitic animals produced a five- and fourfold increase, respectively, in the activity of these enzymes. Vitamin D3 also increased the peroxisomal fatty acid oxidation and the accumulation of glycogen in liver slices in the presence of palmitate. These data suggest that the mammalian rat liver can convert fatty acid carbon to carbohydrate carbon directly.

Topics: Animals; Cholecalciferol; Fatty Acids; Glycogen; Glyoxylates; Isocitrate Lyase; Liver; Malate Synthase; Microbodies; NAD; Oxidation-Reduction; Palmitic Acid; Palmitic Acids; Rats; Rats, Inbred Strains; Vitamin D Deficiency

The effect of vitamin-D deficiency and subsequent vitamin-D replacement on the metabolism of rat epiphyseal growth plate cartilage was studied. Biochemical analyses showed the presence of the two unique glyoxylate cycle enzymes isocitrate lyase and malate synthase in cartilage. The activity of these enzymes was markedly increased after treatment with the vitamin. Additionally, rat cartilage showed the capacity to oxidize fatty acid in the presence of cyanide. This cyanide-insensitive fatty acid oxidation is characteristic of peroxisomal B-oxidation rather than mitochondrial B-oxidation. Vitamin-D treatment also increased fatty acid oxidation. Lastly, incubation of rat cartilage in the presence of a fatty acid substrate such as palmitate, resulted in a higher tissue glycogen content. Tissue glycogen was further elevated by vitamin-D. Such data indicate the presence of glyoxylate cycle enzymes in a vertebrate tissue and raise the possibility that mammalian cartilage has the capacity to convert lipid to carbohydrate.

Topics: Animals; Cholecalciferol; Cyanides; Fatty Acids; Glycogen; Glyoxylates; Growth Plate; Isocitrate Lyase; Malate Synthase; Oxidation-Reduction; Palmitates; Rats; Rats, Inbred Strains; Vitamin D Deficiency

Topics: Alkaline Phosphatase; Bone and Bones; Calcinosis; Calcium; Collagen; Endoplasmic Reticulum; Glycogen; Humans; Hyperparathyroidism; Microscopy, Electron; Mitochondria; Osteoblasts; Osteomalacia; Phosphates; Ribosomes; Vitamin D Deficiency

Topics: Animals; Epiphyses; Glycogen; Glycolysis; Growth Plate; Oxidation-Reduction; Pyruvates; Pyruvic Acid; Rats; Rickets; Vitamin D; Vitamin D Deficiency