Changes in Expression and Cellular Localization of Rat Skeletal Muscle ClC-1 Chloride Channel in Relation to Age, Myofiber Phenotype and PKC Modulation

Branched-chain amino acids and L-alanine supplementation ameliorate calcium dyshomeostasis in sarcopenia: New insights for nutritional interventions

Introduction: During aging, sarcopenia and decline in physiological processes lead to partial loss of muscle strength, atrophy, and increased fatigability. Muscle changes may be related to a reduced intake of essential amino acids playing a role in proteostasis. We have recently shown that branched-chain amino acid (BCAA) supplements improve atrophy and weakness in models of muscle disuse and aging. Considering the key roles that the alteration of Ca2+-related homeostasis and store-operated calcium entry (SOCE) play in several muscle dysfunctions, this study has been aimed at gaining insight into the potential ability of BCAA-based dietary formulations in aged mice on various players of Ca2+ dyshomeostasis. Methods: Seventeen-month-old male C57BL/6J mice received a 12-week supplementation with BCAAs alone or boosted with two equivalents of L-alanine (2-Ala) or with dipeptide L-alanyl-L-alanine (Di-Ala) in drinking water. Outcomes were evaluated on ex vivo skeletal muscles indices vs. adult 3-month-old male C57BL/6J mice. Results: Ca2+ imaging confirmed a decrease in SOCE and an increase of resting Ca2+ concentration in aged vs. adult mice without alteration in the canonical components of SOCE. Aged muscles vs. adult muscles were characterized by a decrease in the expression of ryanodine receptor 1 (RyR1), the Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) pump, and sarcalumenin together with an alteration of the expression of mitsugumin 29 and mitsugumin 53, two recently recognized players in the SOCE mechanism. BCAAs, particularly the formulation BCAAs+2-Ala, were able to ameliorate all these alterations. Discussion: These results provide evidence that Ca2+ homeostasis dysfunction plays a role in the functional deficit observed in aged muscle and supports the interest of dietary BCAA supplementation in counteracting sarcopenia-related SOCE dysregulation.

Correction of Clcn1 alternative splicing reverses muscle fiber type transition in mice with myotonic dystrophy

In myotonic dystrophy type 1 (DM1), deregulated alternative splicing of the muscle chloride channel Clcn1 causes myotonia, a delayed relaxation of muscles due to repetitive action potentials. The degree of weakness in adult DM1 is associated with increased frequency of oxidative muscle fibers. However, the mechanism for glycolytic-to-oxidative fiber type transition in DM1 and its relationship to myotonia are uncertain. Here we cross two mouse models of DM1 to create a double homozygous model that features progressive functional impairment, severe myotonia, and near absence of type 2B glycolytic fibers. Intramuscular injection of an antisense oligonucleotide for targeted skipping of Clcn1 exon 7a corrects Clcn1 alternative splicing, increases glycolytic 2B levels to ≥ 40% frequency, reduces muscle injury, and improves fiber hypertrophy relative to treatment with a control oligo. Our results demonstrate that fiber type transitions in DM1 result from myotonia and are reversible, and support the development of Clcn1-targeting therapies for DM1.

Quantitative aspects of nitric oxide production from nitrate and nitrite

Nitric oxide (NO) is involved in many physiological and pathological processes in the human body. At least two major pathways produce NO: (1) the L-arginine-NO-oxidative pathway in which NO synthase (NOS) enzymes convert L-arginine to NO; (2) the nitrate-nitrite-NO reductive pathway in which NO is produced from the serial reduction of nitrate and nitrite. The deficiency of NO is involved in the pathophysiology of cardiometabolic disorders. Intervention with foods containing nitrate and nitrite can potentially prevent or treat some chronic diseases, including cardiovascular diseases and diabetes. A better understanding of the NO cycle would help develop effective strategies for preventing or treating the disorders in which NO homeostasis is disturbed. This review summarizes quantitative aspects of NO production, emphasizing the nitrate-nitrite-NO pathway. Available data indicates that total NO production by NOS-dependent L-arginine-NO pathway is about 1000 μmol.day-1. Of about 1700 μmol.day-1 ingested nitrate, ~25 % is extracted by the salivary glands and of which ~20 % is converted nitrite. It means that about 5 % of ingested nitrate is converted to nitrite in the oral cavity; assuming that all produced nitrite is reduced to NO in the stomach, it can be calculated that contribution of the nitrate-nitrite-NO pathway to the whole-body NO production is about 85 μmol.day-1 (1700 ×0.05=85) or approximately 100 μmol.day-1. The lower contribution of the nitrate-nitrite-NO pathway does not mean that this pathway has lower importance in the whole-body NO homeostasis. Even in the adequate L-arginine supply, NOS-dependent NO production is insufficient to meet all NO functions, and the nitrate-nitrite-NO pathway must provide the rest. In conclusion, the contribution of the nitrate-nitrite-NO pathway in the whole human body NO production is <10 %, and the nitrate-nitrite-NO pathway is complementary to the NOS-dependent NO production.

Statin-Induced Myopathy: Translational Studies from Preclinical to Clinical Evidence

Statins are the most prescribed and effective drugs to treat cardiovascular diseases (CVD). Nevertheless, these drugs can be responsible for skeletal muscle toxicity which leads to reduced compliance. The discontinuation of therapy increases the incidence of CVD. Thus, it is essential to assess the risk. In fact, many studies have been performed at preclinical and clinical level to investigate pathophysiological mechanisms and clinical implications of statin myotoxicity. Consequently, new toxicological aspects and new biomarkers have arisen. Indeed, these drugs may affect gene transcription and ion transport and contribute to muscle function impairment. Identifying a marker of toxicity is important to prevent or to cure statin induced myopathy while assuring the right therapy for hypercholesterolemia and counteracting CVD. In this review we focused on the mechanisms of muscle damage discovered in preclinical and clinical studies and highlighted the pathological situations in which statin therapy should be avoided. In this context, preventive or substitutive therapies should also be evaluated.