Duchenne muscular dystrophy (DMD) is characterized by a severe and progressive destruction of muscle fibers associated with altered Ca
homeostasis. We have previously shown that the IP
receptor (IP
...R) plays a role in elevating basal cytoplasmic Ca
and that pharmacological blockade of IP
R restores muscle function. Moreover, we have shown that the IP
R pathway negatively regulates autophagy by controlling mitochondrial Ca
levels. Nevertheless, it remains unclear whether IP
R is involved in abnormal mitochondrial Ca
levels, mitochondrial dynamics, or autophagy and mitophagy observed in adult DMD skeletal muscle. Here, we show that the elevated basal autophagy and autophagic flux levels were normalized when IP
R was downregulated in mdx fibers. Pharmacological blockade of IP
R in mdx fibers restored both increased mitochondrial Ca
levels and mitochondrial membrane potential under resting conditions. Interestingly, mdx mitochondria changed from a fission to an elongated state after IP
R knockdown, and the elevated mitophagy levels in mdx fibers were normalized. To our knowledge, this is the first study associating IP
R1 activity with changes in autophagy, mitochondrial Ca
levels, mitochondrial membrane potential, mitochondrial dynamics, and mitophagy in adult mouse skeletal muscle. Moreover, these results suggest that increased IP
R activity in mdx fibers plays an important role in the pathophysiology of DMD. Overall, these results lead us to propose the use of specific IP
R blockers as a new pharmacological treatment for DMD, given their ability to restore both autophagy/mitophagy and mitochondrial function.
Duchenne muscular dystrophy (DMD) is a common genetic disorder characterized by a severe muscle wasting caused by the absence of dystrophin. In mdx muscle fibers, we have shown that basal ATP release ...is increased and that high extracellular ATP is a pro‐apoptotic stimuli. We also have shown that Dihydropyridine receptors (DHPR) are needed for ATP release through pannexin‐1(Pnx1) channels. The aim of this work was to study the potential therapeutic effect of DHPR blockage by nifedipine in DMD. We used muscle fibers isolated from six‐week‐old normal and mdx mice that were treated with daily intraperitoneal injections of 1mg/Kg nifedipine for 1‐week. We studied differences in the interaction between DHPR and Pnx1by proximity ligation assay. In mdx fibers there was an increase in the number and volume of positive particles but not in the intensity of the positive reaction when compared to normal fibers. After the treatment with nifedipine, both number and volume of the positive reaction particles was normalized. This result correlates well with a decrease in both ATP release and intracellular resting Ca2+ concentration in mdx fibers after the treatment. Moreover, ATP signaling was no longer a pro‐apoptotic stimuli. Finally, nifedipine treatment increased muscle strength assessed by both the inverted grip‐hanging and forced swimming test. These data suggest that dihydropyridines can be used as a therapeutical tool to reduce muscle damage observed in dystrophic muscles.
Grant Funding Source: Fondecyt 1110467, ACT1111, AFM14562, AT‐24110211
Adipose tissue is essential for whole-body glucose homeostasis, with a primary role in lipid storage. It has been previously observed that lactate production is also an important metabolic feature of ...adipocytes, but its relationship to adipose and whole-body glucose disposal remains unclear. Therefore, using a combination of metabolic labeling techniques, here we closely examined lactate production of cultured and primary mammalian adipocytes. Insulin treatment increased glucose uptake and conversion to lactate, with the latter responding more to insulin than did other metabolic fates of glucose. However, lactate production did not just serve as a mechanism to dispose of excess glucose, because we also observed that lactate production in adipocytes did not solely depend on glucose availability and even occurred independently of glucose metabolism. This suggests that lactate production is prioritized in adipocytes. Furthermore, knocking down lactate dehydrogenase specifically in the fat body of Drosophila flies lowered circulating lactate and improved whole-body glucose disposal. These results emphasize that lactate production is an additional metabolic role of adipose tissue beyond lipid storage and release.
Introduction: Fibroblast growth factor 21 (FGF21) is a pleiotropic peptide hormone that induces glucose uptake in both primary myotubes and C2C12 myoblasts. However, the cellular mechanism involved ...and its role in adult skeletal muscle fibers is poorly understood. Material and Methods: Male mice were used at 6-8 weeks of age. The glucose uptake was evaluated in single living fibers from flexor digitorum brevis muscle. To determine glucose uptake, we used the phosphorylable, non-metabolizable fluorescent glucose analog 2-NBDG (300 µM) that has been used to monitor glucose uptake in single living cells. Results: FGF21 induces a dose-response effect, increasing glucose uptake in isolated skeletal muscle fibers. This effect is prevented by the use of either Cytochalasin B (5 µM) or Indinavir (100 µM), both antagonists of GLUT4 activity. The use of PI3K inhibitors such as Wortmannin (100 nM) and LY294002 (50 µM) prevents the FGF21-dependent glucose uptake. In fibers electroporated with the construct encoding GLUT4myc-eGFP chimera and stimulated with FGF21 (100 ng/mL) for 20 min, a strong sarcolemmal GLUT4 presence was detected. This effect, promoted by FGF21, is independent of Akt phosphorylation and is partially prevented by the inhibition of PKCs. Conclusions: These results suggest that FGF21 regulates glucose uptake by a mechanism dependent on PI3K activity and independent of Akt phosphorylation. Keywords: Fibroblast growth factor 21, glucose uptake, GLUT4-dependent and Akt-independent mechanism, isolated fibers, skeletal muscle Financed by FONDECYT (1151293, 11130267, and 11150243)
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