Permanent fatty acid translocase (FAT/)CD36 relocation has previously been shown to be related to abnormal lipid accumulation in the skeletal muscle of type 2 diabetic patients, however mechanisms responsible for the regulation of FAT/CD36 expression and localization are not well characterized in human skeletal muscle.
Primary muscle cells derived from obese type 2 diabetic patients (OBT2D) and from healthy subjects (Control) were used to examine the regulation of FAT/CD36. We showed that compared to Control myotubes, FAT/CD36 was continuously cycling between intracellular compartments and the cell surface in OBT2D myotubes, independently of lipid raft association, leading to increased cell surface FAT/CD36 localization and lipid accumulation. Moreover, we showed that FAT/CD36 cycling and lipid accumulation were specific to myotubes and were not observed in reserve cells. However, in Control myotubes, the induction of FAT/CD36 membrane translocation by the activation of (AMP)-activated protein kinase (AMPK) pathway did not increase lipid accumulation. This result can be explained by the fact that pharmacological activation of AMPK leads to increased mitochondrial beta-oxidation in Control cells.
Lipid accumulation in myotubes derived from obese type 2 diabetic patients arises from abnormal FAT/CD36 cycling while lipid accumulation in Control cells results from an equilibrium between lipid uptake and oxidation. As such, inhibiting FAT/CD36 cycling in the skeletal muscle of obese type 2 diabetic patients should be sufficient to diminish lipid accumulation.
We propose an innovative, integrated, cost-effective health system to combat major non-communicable diseases (NCDs), including cardiovascular, chronic respiratory, metabolic, rheumatologic and neurologic disorders and cancers, which together are the predominant health problem of the 21st century. This proposed holistic strategy involves comprehensive patient-centered integrated care and multi-scale, multi-modal and multi-level systems approaches to tackle NCDs as a common group of diseases. Rather than studying each disease individually, it will take into account their intertwined gene-environment, socio-economic interactions and co-morbidities that lead to individual-specific complex phenotypes. It will implement a road map for predictive, preventive, personalized and participatory (P4) medicine based on a robust and extensive knowledge management infrastructure that contains individual patient information. It will be supported by strategic partnerships involving all stakeholders, including general practitioners associated with patient-centered care. This systems medicine strategy, which will take a holistic approach to disease, is designed to allow the results to be used globally, taking into account the needs and specificities of local economies and health systems.
The present study investigated whether muscular monocarboxylate transporter (MCT) 1 and 4 contents are related to the blood lactate removal after supramaximal exercise, fatigue indexes measured during different supramaximal exercises, and muscle oxidative parameters in 15 humans with different training status. Lactate recovery curves were obtained after a 1-min all-out exercise. A bi-exponential time function was then used to determine the velocity constant of the slow phase (γ2), which denoted the blood lactate removal ability. Fatigue indexes were calculated during 1-min all-out (FIAO) and repeated 10-s (FISprint) cycling sprints. Biopsies were taken from the vastus lateralis muscle. MCT1 and MCT4 contents were quantified by Western blots, and maximal muscle oxidative capacity (Vmax) was evaluated with pyruvate + malate and glutamate + malate as substrates. The results showed that the blood lactate removal ability (i.e., γ2)) after a 1-min all-out test was significantly related to MCT1 content (r=0.70, P <0.01) but not to MCT4 (r=0.50, P >0.05). However, greater MCT1 and MCT4 contents were negatively related with a reduction of blood lactate concentration at the end of 1-min all-out exercise (r =− 0.56, and r= −0.61, P < 0.05, respectively). Among skeletal muscle oxidative indexes, we only found a relationship between MCT1 and glutamate + malate Vmax (r = 0.63, P < 0.05). Furthermore, MCT1 content, but not MCT4, was inversely related to FIAO (r =−0.54, P < 0.05) and FISprint (r r =0.58, P <0.05). We concluded that skeletal muscle MCT1 expression was associated with the velocity constant of net blood lactate removal after a 1-min all-out test and with the fatigue indexes. It is proposed that MCT1 expression may be important for blood lactate removal after supramaximal exercise based on the existence of lactate shuttles and, in turn, in favor of a better tolerance to muscle fatigue
Adult; Anaerobic Threshold; physiology; Exercise Test; Humans; Lactic Acid; blood; Male; Monocarboxylic Acid Transporters; metabolism; Muscle Fatigue; physiology; Muscle, Skeletal; physiology; Physical Endurance; physiology; Symporters; metabolism; Lactate kinetics; bi-exponential mathematical model; all-out exercise
Facioscapulohumeral dystrophy (FSHD) is a muscular hereditary disease with a prevalence of 1 in 20 000 caused by a partial deletion of a subtelomeric repeat array on chromosome 4q. However, very little is known about the pathogenesis as well as the molecular and biochemical changes linked to the progressive muscle degeneration observed in these patients. Several studies have investigated possible pathophysiological pathways in FSHD myoblasts and mature muscle cells but some of these reports were apparently in contradiction. The discrepancy between these studies may be explained by differences between the sources of myoblasts. Therefore, we decided to thoroughly analyse affected and unaffected muscles from patients with FSHD in terms of vulnerability to oxidative stress, differentiation capacity and morphological abnormalities.
We have established a panel of primary myoblast cell cultures from patients affected with FSHD and matched healthy individuals. Our results show that primary myoblasts are more susceptible to an induced oxidative stress than control myoblasts. Moreover, we demonstrate that both types of FSHD primary myoblasts differentiate into multinucleated myotubes which present morphological abnormalities. Whereas control myoblasts fuse to form branched myotubes with aligned nuclei, FSHD myoblasts fuse to form either thin and branched myotubes with aligned nuclei or large myotubes with random nuclei distribution.
In conclusion, we postulate that these abnormalities could be responsible for muscle weakness in patients with FSHD and provide an important marker for FSHD myoblasts.
Facioscapulohumeral dystrophy (FSHD); muscle differentiation; myoblasts; oxidative stress; cellular model
The contractile activity of striated muscle depends on myofibrils that are highly ordered macromolecular complexes. The protein components of myofibrils are well characterized, but it remains largely unclear how signaling at the molecular level within the sarcomere and the control of assembly are coordinated. We show that the Rho GTPase TC10 appears during differentiation of human primary skeletal myoblasts and it is active in differentiated myotubes. We identify obscurin, a sarcomere-associated protein, as a specific activator of TC10. Indeed, TC10 binds directly to obscurin via its predicted RhoGEF motif. Importantly, we demonstrate that obscurin is a specific activator of TC10 but not the Rho GTPases Rac and Cdc42. Finally, we show that inhibition of TC10 activity by expression of a dominant-negative mutant or its knockdown by expression of specific shRNA block myofibril assembly. Our findings reveal a novel signaling pathway in human skeletal muscle that involves obscurin and the Rho GTPase TC10 and implicate this pathway in new sarcomere formation.
Cell Differentiation; Cells, Cultured; Enzyme Activation; Guanine Nucleotide Exchange Factors; chemistry; metabolism; Humans; Muscle Fibers, Skeletal; cytology; enzymology; Muscle Proteins; chemistry; metabolism; Myofibrils; enzymology; Organogenesis; Phosphorylation; Protein Binding; Protein Structure, Tertiary; RNA, Small Interfering; metabolism; Sarcomeres; enzymology; metabolism; p21-Activated Kinases; metabolism; rho GTP-Binding Proteins; antagonists & inhibitors; metabolism; Myofibrillogenesis; Rho GTPase; Obscurin
The effects of hypercapnic acidosis on the diaphragm and its recovery to normocapnia have been poorly evaluated. We studied diaphragmatic contractility facing acute variations of PaCO2 and evaluated the contractile function at 60 min after normocapnia recovery.
Thirteen piglets weighing 15–20 kg were anesthetized, ventilated and separated into two groups: a control group (n= 5) evaluated in normocapnia (time-control experiments) and a hypercapnia group (n= 8) in which animals were acutely and shortly exposed to five consecutive ranges of PaCO2 (40, 50, 70, 90 and 110 mmHg). Then CO2 insufflation was stopped. Diaphragmatic contractility was assessed by measuring transdiaphragmatic pressure (Pdi) variations obtained after bilateral transjugulary phrenic pacing at increased frequencies (20–120 Hz). For each level of PaCO2, pressure-frequency curves were obtained in vivo by phrenic nerve pacing.
In the hypercapnia group, mean (±SD) Pdi significantly decreased from 41 ± 3 to 29 ± 3 cmH2O (P<0.05) between the first (40 mmHg) and the fifth stages of capnia (116 mmHg) at the frequency of 100 Hz stimulation. The observed alteration of the contractile force was proportional to the level of PaCO2 (r2= 0.61, P<0.01). Normocapnia recuperation allowed a partial recovery of the diaphragmatic contractile force (80% of the baseline value) at 60 min after CO2 insufflation interruption.
A short exposure to respiratory acidosis decreased diaphragmatic contractility proportionally to the degree of hypercapnia and this alteration was only partially reversed at 60 min following exposure.
Acute Disease; Animals; Animals, Newborn; Diaphragm; physiology; Hypercapnia; physiopathology; Muscle Contraction; physiology; Recovery of Function; physiology; Swine
In the peripheral nervous system, utrophin and the short dystrophin isoform (Dp116) are co-localized at the outermost layer of the myelin sheath of nerve fibers; together with the dystroglycan complex. Dp116 is associated with multiple glycoproteins, i.e. sarcoglycans, and α-and β-dystroglycan, which anchor the cytoplasmic protein subcomplex to the extracellular basal lamina. In peripheral nerve, matrix metalloproteinase (MMP) activity disrupts the dystroglycan complex by cleaving the extracellular domain of β-dystroglycan. MMP creates a 30 kDa fragment of β-dystroglycan, leading to a disruption of the link between the extracellular matrix and the cell membrane. In this study, we investigated the molecular interactions of full length and 30 kDa β-dystroglycan with Dp116 and utrophins in peripheral nerve Schwann cells from normal and mdx mice. Our results showed that Dp116 had greater affinity to the glycosylated form of β-dystroglycan than the 30 kDa form. Interestingly, the short isoform of utrophin (Up71) was highly expressed in mdx Schwann cells compared with normal Schwann cells. In contrast to Dp116, Up71 had greater affinity to the 30 kDa β-dystroglycan. These results are discussed with regard to the participation of the short utrophin isoform and the cleaved form of β-dystroglycan in mdx Schwann cell membrane architecture and their possible role in peripheral nerve physiology.
Animals; Blotting, Western; methods; Cell Membrane; drug effects; metabolism; Dystroglycans; metabolism; Dystrophin; metabolism; Immunohistochemistry; methods; Immunoprecipitation; methods; Matrix Metalloproteinase 9; pharmacology; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; metabolism; Models, Biological; Reverse Transcriptase Polymerase Chain Reaction; methods; S100 Proteins; metabolism; Schwann Cells; cytology; drug effects; Sciatic Nerve; cytology; Statistics, Nonparametric; Utrophin; metabolism; Mouse peripheral nerve; Schwann cell; Utrophin short isoform; Dystroglycan; MMP2; MMP9
Previous studies have shown a blunted ventilatory response to hypercapnia in mdx mice older than 7 months. We test the hypothesis that in the mdx mice ventilatory response changes with age, concomitantly with the increased functional impairment of the respiratory muscles. We thus studied the ventilatory response to CO2 in 5 and 16 month-old mdx and C57BL10 mice (n = 8 for each group). Respiratory rate (RR), tidal volume (VT), and minute ventilation (VE) were measured, using whole-body plethysmography, during air breathing and in response to hypercapnia (3, 5 and 8% CO2). The ventilatory protocol was completed by histological analysis of the diaphragm and intercostals muscles. During air breathing, the 16 month-old mdx mice showed higher RR and, during hypercapnia (at 8% CO2 breathing), significantly lower RR (226 ± 26 vs. 270 ± 21 breaths/min) and VE (1.81 ± 0.35 vs. 3.96 ± 0.59 ml min−1 g−1)(P < 0.001) in comparison to C57BL10 controls. On the other hand, 5 month-old C57BL10 and mdx mice did not present any difference in their ventilatory response to air breathing and to hypercapnia. In conclusion, this study shows similar ventilation during air breathing and in response to hypercapnia in the 5 month-old mdx and control mice, in spite of significant pathological structural changes in the respiratory muscles of the mdx mice. However in the 16 month-old mdx mice we observed altered ventilation under air and blunted ventilation response to hypercapnia compared to age-matched control mice. Ventilatory response to hypercapnia thus changes with age in mdx mice, in line with the increased histological damage of their respiratory muscles.
Age; Duchenne muscular dystrophy; Hypercapnia mdx mouse; Ventilatory response