Dapagliflozin protects the kidney in a non-diabetic model of cardiorenal syndrome.

Cardiorenal syndrome encompasses a spectrum of disorders involving heart and kidney dysfunction, and sharing common risk factors, such as hypertension and diabetes. Clinical studies have shown that patients with and without diabetes may benefit from using sodium-glucose cotransporter 2 inhibitors to reduce the risk of heart failure and ameliorate renal endpoints. Because the underlying mechanisms remain elusive, we investigated the effects of dapagliflozin on the progression of renal damage, using a model of non-diabetic cardiorenal disease. Dahl salt-sensitive rats were fed a high-salt diet for five weeks and then randomized to dapagliflozin or vehicle for the following six weeks. After treatment with dapagliflozin, renal function resulted ameliorated as shown by decrease of albuminuria and urine albumin-to-creatinine ratio. Functional benefit was accompanied by a decreased accumulation of extracellular matrix and a reduced number of sclerotic glomeruli. Dapagliflozin significantly reduced expression of inflammatory and endothelial activation markers such as NF-κB and e-selectin. Upregulation of pro-oxidant-releasing NADPH oxidases 2 and 4 as well as downregulation of antioxidant enzymes were also counteracted by drug treatment. Our findings also evidenced the modulation of both classic and non-classic renin-angiotensin-aldosterone system (RAAS), and effects of dapagliflozin on gene expression of ion channels/transporters involved in renal homeostasis. Thus, in a non-diabetic model of cardiorenal syndrome, dapagliflozin provides renal protection by modulating inflammatory response, endothelial activation, fibrosis, oxidative stress, local RAAS and ion channels.

BCAAs and Di-Alanine supplementation in the prevention of skeletal muscle atrophy: preclinical evaluation in a murine model of hind limb unloading.

Skeletal muscle atrophy occurs in response to various pathophysiological stimuli, including disuse, aging, and neuromuscular disorders, mainly due to an imbalance of anabolic/catabolic signaling. Branched Chain Amino Acids (BCAAs: leucine, isoleucine, valine) supplements can be beneficial for counteracting muscle atrophy, in virtue of their reported anabolic properties. Here, we carried out a proof-of-concept study to assess the in vivo/ex vivo effects of a 4-week treatment with BCAAs on disuse-induced atrophy, in a murine model of hind limb unloading (HU). BCAAs were formulated in drinking water, alone, or plus two equivalents of L-Alanine (2 ALA) or the dipeptide L-Alanyl-L-Alanine (Di-ALA), to boost BCAAs bioavailability. HU mice were characterized by reduction of body mass, decrease of soleus - SOL - muscle mass and total protein, alteration of postural muscles architecture and fiber size, dysregulation of atrophy-related genes (Atrogin-1, MuRF-1, mTOR, Mstn). In parallel, we provided new robust readouts in the HU murine model, such as impaired in vivo isometric torque and ex vivo SOL muscle contractility and elasticity, as well as altered immune response. An acute pharmacokinetic study confirmed that L-ALA, also as dipeptide, enhanced plasma exposure of BCAAs. Globally, the most sensitive parameters to BCAAs action were muscle atrophy and myofiber cross-sectional area, muscle force and compliance to stress, protein synthesis via mTOR and innate immunity, with the new BCAAs + Di-ALA formulation being the most effective treatment. Our results support the working hypothesis and highlight the importance of developing innovative formulations to optimize BCAAs biodistribution.

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.

Ryanodine channel complex stabilizer compound S48168/ARM210 as a disease modifier in dystrophin-deficient mdx mice: proof-of-concept study and independent validation of efficacy.

Muscle fibers lacking dystrophin undergo a long-term alteration of Ca2+ homeostasis, partially caused by a leaky Ca2+ release ryanodine (RyR) channel. S48168/ARM210, an RyR calcium release channel stabilizer (a Rycal compound), is expected to enhance the rebinding of calstabin to the RyR channel complex and possibly alleviate the pathologic Ca2+ leakage in dystrophin-deficient skeletal and cardiac muscle. This study systematically investigated the effect of S48168/ARM210 on the phenotype of mdx mice by means of a first proof-of-concept, short (4 wk), phase 1 treatment, followed by a 12-wk treatment (phase 2) performed in parallel by 2 independent laboratories. The mdx mice were treated with S48168/ARM210 at two different concentrations (50 or 10 mg/kg/d) in their drinking water for 4 and 12 wk, respectively. The mice were subjected to treadmill sessions twice per week (12 m/min for 30 min) to unmask the mild disease. This testing was followed by in vivo forelimb and hindlimb grip strength and fatigability measurement, ex vivo extensor digitorum longus (EDL) and diaphragm (DIA) force contraction measurement and histologic and biochemical analysis. The treatments resulted in functional (grip strength, ex vivo force production in DIA and EDL muscles) as well as histologic improvement after 4 and 12 wk, with no adverse effects. Furthermore, levels of cellular biomarkers of calcium homeostasis increased. Therefore, these data suggest that S48168/ARM210 may be a safe therapeutic option, at the dose levels tested, for the treatment of Duchenne muscular dystrophy (DMD).-Capogrosso, R. F., Mantuano, P., Uaesoontrachoon, K., Cozzoli, A., Giustino, A., Dow, T., Srinivassane, S., Filipovic, M., Bell, C., Vandermeulen, J., Massari, A. M., De Bellis, M., Conte, E., Pierno, S., Camerino, G. M., Liantonio, A., Nagaraju, K., De Luca, A. Ryanodine channel complex stabilizer compound S48168/ARM210 as a disease modifier in dystrophin-deficient mdx mice: proof-of-concept study and independent validation of efficacy.

Multidisciplinary study of a new ClC-1 mutation causing myotonia congenita: a paradigm to understand and treat ion channelopathies.

Myotonia congenita is an inherited disease that is characterized by impaired muscle relaxation after contraction caused by loss-of-function mutations in the skeletal muscle ClC-1 channel. We report a novel ClC-1 mutation, T335N, that is associated with a mild phenotype in 1 patient, located in the extracellular I-J loop. The purpose of this study was to provide a solid correlation between T335N dysfunction and clinical symptoms in the affected patient as well as to offer hints for drug development. Our multidisciplinary approach includes patch-clamp electrophysiology on T335N and ClC-1 wild-type channels expressed in tsA201 cells, Western blot and quantitative PCR analyses on muscle biopsies from patient and unaffected individuals, and molecular dynamics simulations using a homology model of the ClC-1 dimer. T335N channels display reduced chloride currents as a result of gating alterations rather than altered surface expression. Molecular dynamics simulations suggest that the I-J loop might be involved in conformational changes that occur at the dimer interface, thus affecting gating. Finally, the gene expression profile of T335N carrier showed a diverse expression of K+ channel genes, compared with control individuals, as potentially contributing to the phenotype. This experimental paradigm satisfactorily explained myotonia in the patient. Furthermore, it could be relevant to the study and therapy of any channelopathy.-Imbrici, P., Altamura, C., Camerino, G. M., Mangiatordi, G. F., Conte, E., Maggi, L., Brugnoni, R., Musaraj, K., Caloiero, R., Alberga, D., Marsano, R. M., Ricci, G., Siciliano, G., Nicolotti, O., Mora, M., Bernasconi, P., Desaphy, J.-F., Mantegazza, R., Camerino, D. C. Multidisciplinary study of a new ClC-1 mutation causing myotonia congenita: a paradigm to understand and treat ion channelopathies.

Gene expression in mdx mouse muscle in relation to age and exercise: aberrant mechanical-metabolic coupling and implications for pre-clinical studies in Duchenne muscular dystrophy.

Weakness and fatigability are typical features of Duchenne muscular dystrophy patients and are aggravated in dystrophic mdx mice by chronic treadmill exercise. Mechanical activity modulates gene expression and muscle plasticity. Here, we investigated the outcome of 4 (T4, 8 weeks of age) and 12 (T12, 16 weeks of age) weeks of either exercise or cage-based activity on a large set of genes in the gastrocnemius muscle of mdx and wild-type (WT) mice using quantitative real-time PCR. Basal expression of the exercise-sensitive genes peroxisome-proliferator receptor γ coactivator 1α (Pgc-1α) and Sirtuin1 (Sirt1) was higher in mdx versus WT mice at both ages. Exercise increased Pgc-1α expression in WT mice; Pgc-1α was downregulated by T12 exercise in mdx muscles, along with Sirt1, Pparγ and the autophagy marker Bnip3. Sixteen weeks old mdx mice showed a basal overexpression of the slow Mhc1 isoform and Serca2; T12 exercise fully contrasted this basal adaptation as well as the high expression of follistatin and myogenin. Conversely, T12 exercise was ineffective in WT mice. Damage-related genes such as gp91-phox (NADPH-oxidase2), Tgfß, Tnfα and c-Src tyrosine kinase were overexpressed in mdx muscles and not affected by exercise. Likewise, the anti-inflammatory adiponectin was lower in T12-exercised mdx muscles. Chronic exercise with minor adaptive effects in WT muscles leads to maladaptation in mdx muscles with a disequilibrium between protective and damaging signals. Increased understanding of the pathways involved in the altered mechanical-metabolic coupling may help guide appropriate physical therapies while better addressing pharmacological interventions in translational research.

Statin-induced myotoxicity is exacerbated by aging: A biophysical and molecular biology study in rats treated with atorvastatin.

Statin-induced skeletal muscle damage in rats is associated to the reduction of the resting sarcolemmal chloride conductance (gCl) and ClC-1 chloride channel expression. These drugs also affect the ClC-1 regulation by increasing protein kinase C (PKC) activity, which phosphorylate and close the channel. Also the intracellular resting calcium (restCa) level is increased. Similar alterations are observed in skeletal muscles of aged rats, suggesting a higher risk of statin myotoxicity. To verify this hypothesis, we performed a 4-5-weeks atorvastatin treatment of 24-months-old rats to evaluate the ClC-1 channel function by the two-intracellular microelectrodes technique as well as transcript and protein expression of different genes sensitive to statins by quantitative real-time-PCR and western blot analysis. The restCa was measured using FURA-2 imaging, and histological analysis of muscle sections was performed. The results show a marked reduction of resting gCl, in agreement with the reduced ClC-1 mRNA and protein expression in atorvastatin-treated aged rats, with respect to treated adult animals. The observed changes in myocyte-enhancer factor-2 (MEF2) expression may be involved in ClC-1 expression changes. The activity of PKC was also increased and further modulate the gCl in treated aged rats. In parallel, a marked reduction of the expression of glycolytic and mitochondrial enzymes demonstrates an impairment of muscle metabolism. No worsening of restCa or histological features was found in statin-treated aged animals. These findings suggest that a strong reduction of gCl and alteration of muscle metabolism coupled to muscle atrophy may contribute to the increased risk of statin-induced myopathy in the elderly.

Assessment of resveratrol, apocynin and taurine on mechanical-metabolic uncoupling and oxidative stress in a mouse model of duchenne muscular dystrophy: A comparison with the gold standard, α-methyl prednisolone.

Antioxidants have a great potential as adjuvant therapeutics in patients with Duchenne muscular dystrophy, although systematic comparisons at pre-clinical level are limited. The present study is a head-to-head assessment, in the exercised mdx mouse model of DMD, of natural compounds, resveratrol and apocynin, and of the amino acid taurine, in comparison with the gold standard α-methyl prednisolone (PDN). The rationale was to target the overproduction of reactive oxygen species (ROS) via disease-related pathways that are worsened by mechanical-metabolic impairment such as inflammation and over-activity of NADPH oxidase (NOX) (taurine and apocynin, respectively) or the failing ROS detoxification mechanisms via sirtuin-1 (SIRT1)-peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) (resveratrol). Resveratrol (100mg/kg i.p. 5days/week), apocynin (38mg/kg/day per os), taurine (1g/kg/day per os), and PDN (1mg/kg i.p., 5days/week) were administered for 4-5 weeks to mdx mice in parallel with a standard protocol of treadmill exercise and the outcome was evaluated with a multidisciplinary approach in vivo and ex vivo on pathology-related end-points and biomarkers of oxidative stress. Resveratrol≥taurine>apocynin enhanced in vivo mouse force similarly to PDN. All the compounds reduced the production of superoxide anion, assessed by dihydroethidium staining, with apocynin being as effective as PDN, and ameliorated electrophysiological biomarkers of oxidative stress. Resveratrol also significantly reduced plasma levels of creatine kinase and lactate dehydrogenase. Force of isolated muscles was little ameliorated. However, the three compounds improved histopathology of gastrocnemius muscle more than PDN. Taurine>apocynin>PDN significantly decreased activated NF-kB positive myofibers. Thus, compounds targeting NOX-ROS or SIRT1/PGC-1α pathways differently modulate clinically relevant DMD-related endpoints according to their mechanism of action. With the caution needed in translational research, the results show that the parallel assessment can help the identification of best adjuvant therapies.

Angiotensin II modulates mouse skeletal muscle resting conductance to chloride and potassium ions and calcium homeostasis via the AT1 receptor and NADPH oxidase.

Angiotensin II (ANG II) plays a role in muscle wasting and remodeling; however, little evidence shows its direct effects on specific muscle functions. We presently investigated the acute in vitro effects of ANG II on resting ionic conductance and calcium homeostasis of mouse extensor digitorum longus (EDL) muscle fibers, based on previous findings that in vivo inhibition of ANG II counteracts the impairment of macroscopic ClC-1 chloride channel conductance (gCl) in the mdx mouse model of muscular dystrophy. By means of intracellular microelectrode recordings we found that ANG II reduced gCl in the nanomolar range and in a concentration-dependent manner (EC50 = 0.06 µM) meanwhile increasing potassium conductance (gK). Both effects were inhibited by the ANG II receptors type 1 (AT1)-receptor antagonist losartan and the protein kinase C inhibitor chelerythrine; no antagonism was observed with the AT2 antagonist PD123,319. The scavenger of reactive oxygen species (ROS) N-acetyl cysteine and the NADPH-oxidase (NOX) inhibitor apocynin also antagonized ANG II effects on resting ionic conductances; the ANG II-dependent gK increase was blocked by iberiotoxin, an inhibitor of calcium-activated potassium channels. ANG II also lowered the threshold for myofiber and muscle contraction. Both ANG II and the AT1 agonist L162,313 increased the intracellular calcium transients, measured by fura-2, with a two-step pattern. These latter effects were not observed in the presence of losartan and of the phospholipase C inhibitor U73122 and the in absence of extracellular calcium, disclosing a Gq-mediated calcium entry mechanism. The data show for the first time that the AT1-mediated ANG II pathway, also involving NOX and ROS, directly modulates ion channels and calcium homeostasis in adult myofibers.

Protein kinase C theta (PKCθ) modulates the ClC-1 chloride channel activity and skeletal muscle phenotype: a biophysical and gene expression study in mouse models lacking the PKCθ.

In skeletal muscle, the resting chloride conductance (gCl), due to the ClC-1 chloride channel, controls the sarcolemma electrical stability. Indeed, loss-of-function mutations in ClC-1 gene are responsible of myotonia congenita. The ClC-1 channel can be phosphorylated and inactivated by protein kinases C (PKC), but the relative contribution of each PKC isoforms is unknown. Here, we investigated on the role of PKCθ in the regulation of ClC-1 channel expression and activity in fast- and slow-twitch muscles of mouse models lacking PKCθ. Electrophysiological studies showed an increase of gCl in the PKCθ-null mice with respect to wild type. Muscle excitability was reduced accordingly. However, the expression of the ClC-1 channel, evaluated by qRT-PCR, was not modified in PKCθ-null muscles suggesting that PKCθ affects the ClC-1 activity. Pharmacological studies demonstrated that although PKCθ appreciably modulates gCl, other isoforms are still active and concur to this role. The modification of gCl in PKCθ-null muscles has caused adaptation of the expression of phenotype-specific genes, such as calcineurin and myocyte enhancer factor-2, supporting the role of PKCθ also in the settings of muscle phenotype. Importantly, the lack of PKCθ has prevented the aging-related reduction of gCl, suggesting that its modulation may represent a new strategy to contrast the aging process.

Immune checkpoint inhibitors and neurotoxicity: a focus on diagnosis and management for a multidisciplinary approach.

INTRODUCTION: Although immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment, the consequential over activation of the immune system is often complicated by adverse events that can affect several organs and systems, including the nervous system. The precise pathophysiology underlying neurological irAEs (n-irAEs) is not completely known. Around 3.8% of patients receiving anti-CTLA-4 agents, 6.1% of patients receiving anti-PD-1/PD-L1, and 12% of patients receiving combination therapies have n-irAEs. Most n-irAEs are low-grade, while severe toxicities have rarely been reported. in this article, we performed an updated literature search on immuno-related neurotoxicity on main medical research database, from February 2017 to December 2023. AREAS COVERED: We have also compared the latest national and international guidelines on n-irAEs management with each other in order to better define patient management. EXPERT OPINION: A multidisciplinary approach appears necessary in the management of oncological patients during immunotherapy. Therefore, in order to better manage these toxicities, we believe that it is essential to collaborate with neurologists specialized in the diagnosis and treatment of n-irAEs, and that a global neurological assessment, both central and peripheral, is necessary before starting immunotherapy, with regular reassessment during treatment.

GLPG0492, a novel selective androgen receptor modulator, improves muscle performance in the exercised-mdx mouse model of muscular dystrophy.

Anabolic drugs may counteract muscle wasting and dysfunction in Duchenne muscular dystrophy (DMD); however, steroids have unwanted side effects. We focused on GLPG0492, a new non-steroidal selective androgen receptor modulator that is currently under development for musculo-skeletal diseases such as sarcopenia and cachexia. GLPG0492 was tested in the exercised mdx mouse model of DMD in a 4-week trial at a single high dose (30 mg/kg, 6 day/week s.c.), and the results were compared with those from the administration of α-methylprednisolone (PDN; 1 mg/kg, i.p.) and nandrolone (NAND, 5 mg/kg, s.c.). This assessment was followed by a 12-week dose-dependence study (0.3-30 mg/kg s.c.). The outcomes were evaluated in vivo and ex vivo on functional, histological and biochemical parameters. Similar to PDN and NAND, GLPG0492 significantly increased mouse strength. In acute exhaustion tests, a surrogate of the 6-min walking test used in DMD patients, GLPG0492 preserved running performance, whereas vehicle- or comparator-treated animals showed a significant increase in fatigue (30-50%). Ex vivo, all drugs resulted in a modest but significant increase of diaphragm force. In parallel, a decrease in the non-muscle area and markers of fibrosis was observed in GLPG0492- and NAND-treated mice. The drugs exerted minor effects on limb muscles; however, electrophysiological biomarkers were ameliorated in extensor digitorum longus muscle. The longer dose-dependence study confirmed the effect on mdx mouse strength and resistance to fatigue and demonstrated the efficacy of lower drug doses on in vivo and ex vivo functional parameters. These results support the interest of further studies of GLPG0492 as a potential treatment for DMD.

Therapeutic Targets in Amyotrophic Lateral Sclerosis: Focus on Ion Channels and Skeletal Muscle.

Amyotrophic Lateral Sclerosis is a neurodegenerative disease caused by progressive loss of motor neurons, which severely compromises skeletal muscle function. Evidence shows that muscle may act as a molecular powerhouse, whose final signals generate in patients a progressive loss of voluntary muscle function and weakness leading to paralysis. This pathology is the result of a complex cascade of events that involves a crosstalk among motor neurons, glia, and muscles, and evolves through the action of converging toxic mechanisms. In fact, mitochondrial dysfunction, which leads to oxidative stress, is one of the mechanisms causing cell death. It is a common denominator for the two existing forms of the disease: sporadic and familial. Other factors include excitotoxicity, inflammation, and protein aggregation. Currently, there are limited cures. The only approved drug for therapy is riluzole, that modestly prolongs survival, with edaravone now waiting for new clinical trial aimed to clarify its efficacy. Thus, there is a need of effective treatments to reverse the damage in this devastating pathology. Many drugs have been already tested in clinical trials and are currently under investigation. This review summarizes the already tested drugs aimed at restoring muscle-nerve cross-talk and on new treatment options targeting this tissue.

Chaperone activity of niflumic acid on ClC-1 chloride channel mutants causing myotonia congenita.

Myotonia congenita (MC) is an inherited rare disease characterized by impaired muscle relaxation after contraction, resulting in muscle stiffness. It is caused by loss-of-function mutations in the skeletal muscle chloride channel ClC-1, important for the stabilization of resting membrane potential and for the repolarization phase of action potentials. Thanks to in vitro functional studies, the molecular mechanisms by which ClC-1 mutations alter chloride ion influx into the cell have been in part clarified, classifying them in "gating-defective" or "expression-defective" mutations. To date, the treatment of MC is only palliative because no direct ClC-1 activator is available. An ideal drug should be one which is able to correct biophysical defects of ClC-1 in the case of gating-defective mutations or a drug capable to recover ClC-1 protein expression on the plasma membrane for trafficking-defective ones. In this study, we tested the ability of niflumic acid (NFA), a commercial nonsteroidal anti-inflammatory drug, to act as a pharmacological chaperone on trafficking-defective MC mutants (A531V, V947E). Wild-type (WT) or MC mutant ClC-1 channels were expressed in HEK293 cells and whole-cell chloride currents were recorded with the patch-clamp technique before and after NFA incubation. Membrane biotinylation assays and western blot were performed to support electrophysiological results. A531V and V947E mutations caused a decrease in chloride current density due to a reduction of ClC-1 total protein level and channel expression on the plasma membrane. The treatment of A531V and V947E-transfected cells with 50 µM NFA restored chloride currents, reaching levels similar to those of WT. Furthermore, no significant difference was observed in voltage dependence, suggesting that NFA increased protein membrane expression without altering the function of ClC-1. Indeed, biochemical experiments confirmed that V947E total protein expression and its plasma membrane distribution were recovered after NFA incubation, reaching protein levels similar to WT. Thus, the use of NFA as a pharmacological chaperone in trafficking defective ClC-1 channel mutations could represent a good strategy in the treatment of MC. Because of the favorable safety profile of this drug, our study may easily open the way for confirmatory human pilot studies aimed at verifying the antimyotonic activity of NFA in selected patients carrying specific ClC-1 channel mutations.

Alteration of STIM1/Orai1-Mediated SOCE in Skeletal Muscle: Impact in Genetic Muscle Diseases and Beyond.

Intracellular Ca2+ ions represent a signaling mediator that plays a critical role in regulating different muscular cellular processes. Ca2+ homeostasis preservation is essential for maintaining skeletal muscle structure and function. Store-operated Ca2+ entry (SOCE), a Ca2+-entry process activated by depletion of intracellular stores contributing to the regulation of various function in many cell types, is pivotal to ensure a proper Ca2+ homeostasis in muscle fibers. It is coordinated by STIM1, the main Ca2+ sensor located in the sarcoplasmic reticulum, and ORAI1 protein, a Ca2+-permeable channel located on transverse tubules. It is commonly accepted that Ca2+ entry via SOCE has the crucial role in short- and long-term muscle function, regulating and adapting many cellular processes including muscle contractility, postnatal development, myofiber phenotype and plasticity. Lack or mutations of STIM1 and/or Orai1 and the consequent SOCE alteration have been associated with serious consequences for muscle function. Importantly, evidence suggests that SOCE alteration can trigger a change of intracellular Ca2+ signaling in skeletal muscle, participating in the pathogenesis of different progressive muscle diseases such as tubular aggregate myopathy, muscular dystrophy, cachexia, and sarcopenia. This review provides a brief overview of the molecular mechanisms underlying STIM1/Orai1-dependent SOCE in skeletal muscle, focusing on how SOCE alteration could contribute to skeletal muscle wasting disorders and on how SOCE components could represent pharmacological targets with high therapeutic potential.

Consequences of SUR2[A478V] Mutation in Skeletal Muscle of Murine Model of Cantu Syndrome.

(1) Background: Cantu syndrome (CS) arises from gain-of-function (GOF) mutations in the ABCC9 and KCNJ8 genes, which encode ATP-sensitive K+ (KATP) channel subunits SUR2 and Kir6.1, respectively. Most CS patients have mutations in SUR2, the major component of skeletal muscle KATP, but the consequences of SUR2 GOF in skeletal muscle are unknown. (2) Methods: We performed in vivo and ex vivo characterization of skeletal muscle in heterozygous SUR2[A478V] (SUR2wt/AV) and homozygous SUR2[A478V] (SUR2AV/AV) CS mice. (3) Results: In SUR2wt/AV and SUR2AV/AV mice, forelimb strength and diaphragm amplitude movement were reduced; muscle echodensity was enhanced. KATP channel currents recorded in Flexor digitorum brevis fibers showed reduced MgATP-sensitivity in SUR2wt/AV, dramatically so in SUR2AV/AV mice; IC50 for MgATP inhibition of KATP currents were 1.9 ± 0.5 × 10-5 M in SUR2wt/AV and 8.6 ± 0.4 × 10-6 M in WT mice and was not measurable in SUR2AV/AV. A slight rightward shift of sensitivity to inhibition by glibenclamide was detected in SUR2AV/AV mice. Histopathological and qPCR analysis revealed atrophy of soleus and tibialis anterior muscles and up-regulation of atrogin-1 and MuRF1 mRNA in CS mice. (4) Conclusions: SUR2[A478V] "knock-in" mutation in mice impairs KATP channel modulation by MgATP, markedly so in SUR2AV/AV, with atrophy and non-inflammatory edema in different skeletal muscle phenotypes.

Gain-of-Function STIM1 L96V Mutation Causes Myogenesis Alteration in Muscle Cells From a Patient Affected by Tubular Aggregate Myopathy.

Tubular Aggregate Myopathy (TAM) is a hereditary ultra-rare muscle disorder characterized by muscle weakness and cramps or myasthenic features. Biopsies from TAM patients show the presence of tubular aggregates originated from sarcoplasmic reticulum due to altered Ca2+ homeostasis. TAM is caused by gain-of-function mutations in STIM1 or ORAI1, proteins responsible for Store-Operated-Calcium-Entry (SOCE), a pivotal mechanism in Ca2+ signaling. So far there is no cure for TAM and the mechanisms through which STIM1 or ORAI1 gene mutation lead to muscle dysfunction remain to be clarified. It has been established that post-natal myogenesis critically relies on Ca2+ influx through SOCE. To explore how Ca2+ homeostasis dysregulation associated with TAM impacts on muscle differentiation cascade, we here performed a functional characterization of myoblasts and myotubes deriving from patients carrying STIM1 L96V mutation by using fura-2 cytofluorimetry, high content imaging and real-time PCR. We demonstrated a higher resting Ca2+ concentration and an increased SOCE in STIM1 mutant compared with control, together with a compensatory down-regulation of genes involved in Ca2+ handling (RyR1, Atp2a1, Trpc1). Differentiating STIM1 L96V myoblasts persisted in a mononuclear state and the fewer multinucleated myotubes had distinct morphology and geometry of mitochondrial network compared to controls, indicating a defect in the late differentiation phase. The alteration in myogenic pathway was confirmed by gene expression analysis regarding early (Myf5, Mef2D) and late (DMD, Tnnt3) differentiation markers together with mitochondrial markers (IDH3A, OGDH). We provided evidences of mechanisms responsible for a defective myogenesis associated to TAM mutant and validated a reliable cellular model usefull for TAM preclinical studies.

The KATP channel is a molecular sensor of atrophy in skeletal muscle.

The involvement of ATP-sensitive K(+) (K(ATP)) channels in the atrophy of slow-twitch (MHC-I) soleus (SOL) and fast-twitch (MHC-IIa) flexor digitorum brevis (FDB) muscles was investigated in vivo in 14-day-hindlimb-unloaded (14-HU) rats, an animal model of disuse, and in vitro in drug-induced muscle atrophy. Patch-clamp and gene expression experiments were performed in combination with measurements of fibre diameters used as an index of atrophy, and with MHC labelling in 14-HU rats and controls. A down-regulation of K(ATP) channel subunits Kir6.2, SUR1 and SUR2B with marked atrophy and incomplete phenotype transition were observed in SOL of 14-HU rats. The observed changes in K(ATP) currents were well correlated with changes in fibre diameters and SUR1 expression, as well as with MHC-IIa expression. Half of the SOL fibres of 14-HU rats had reduced diameter and K(ATP) currents and were labelled by MHC-I antibodies. Non-atrophic fibres were labelled by MHC-IIa (22%) antibodies and had enhanced K(ATP) currents, or were labelled by MHC-I (28%) antibodies but had normal current. FDB was not affected in 14-HU rats and this is related to the high expression/activity of Kir6.2/SUR1 subunits characterizing this muscle phenotype. The long-term incubation of the control muscles in vitro with the K(ATP) channel blocker glibenclamide (10(6)m) reduced the K(ATP) currents with atrophy and these effects were prevented by the K(ATP) channel opener diazoxide (10(4)m). The in vivo down-regulation of SUR1, and possibly of Kir6.2 and SUR2B, or their in vitro pharmacological blockade activates atrophic signalling in skeletal muscle. All these findings suggest a new role for the K(ATP) channel as a molecular sensor of atrophy.

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

The ClC-1 chloride channel 1 is important for muscle function as it stabilizes resting membrane potential and helps to repolarize the membrane after action potentials. We investigated the contribution of ClC-1 to adaptation of skeletal muscles to needs induced by the different stages of life. We analyzed the ClC-1 gene and protein expression as well as mRNA levels of protein kinase C (PKC) alpha and theta involved in ClC-1 modulation, in soleus (SOL) and extensor digitorum longus (EDL) muscles of rats in all stage of life. The cellular localization of ClC-1 in relation to age was also investigated. Our data show that during muscle development ClC-1 expression differs according to phenotype. In fast-twitch EDL muscles ClC-1 expression increased 10-fold starting at 7 days up to 8 months of life. Conversely, in slow-twitch SOL muscles ClC-1 expression remained constant until 33 days of life and subsequently increased fivefold to reach the adult value. Aging induced a downregulation of gene and protein ClC-1 expression in both muscle types analyzed. The mRNA of PKC-theta revealed the same trend as ClC-1 except in old age, whereas the mRNA of PKC-alpha increased only after 2 months of age. Also, we found that the ClC-1 is localized in both membrane and cytoplasm, in fibers of 12-day-old rats, becoming perfectly localized on the membrane in 2-month-old rats. This study could represent a point of comparison helpful for the identification of accurate pharmacological strategies for all the pathological situations in which ClC-1 protein is altered.

Pathomechanisms of a CLCN1 Mutation Found in a Russian Family Suffering From Becker's Myotonia.

Objective: Myotonia congenita (MC) is a rare muscle disease characterized by sarcolemma over-excitability inducing skeletal muscle stiffness. It can be inherited either as an autosomal dominant (Thomsen's disease) or an autosomal recessive (Becker's disease) trait. Both types are caused by loss-of-function mutations in the CLCN1 gene, encoding for ClC-1 chloride channel. We found a ClC-1 mutation, p.G411C, identified in Russian patients who suffered from a severe form of Becker's disease. The purpose of this study was to provide a solid correlation between G411C dysfunction and clinical symptoms in the affected patient. Methods: We provide clinical and genetic information of the proband kindred. Functional studies include patch-clamp electrophysiology, biotinylation assay, western blot analysis, and confocal imaging of G411C and wild-type ClC-1 channels expressed in HEK293T cells. Results: The G411C mutation dramatically abolished chloride currents in transfected HEK cells. Biochemical experiments revealed that the majority of G411C mutant channels did not reach the plasma membrane but remained trapped in the cytoplasm. Treatment with the proteasome inhibitor MG132 reduced the degradation rate of G411C mutant channels, leading to their expression at the plasma membrane. However, despite an increase in cell surface expression, no significant chloride current was recorded in the G411C-transfected cell treated with MG132, suggesting that this mutation produces non-functional ClC-1 chloride channels. Conclusion: These results suggest that the molecular pathophysiology of G411C is linked to a reduced plasma membrane expression and biophysical dysfunction of mutant channels, likely due to a misfolding defect. Chloride current abolition confirms that the mutation is responsible for the clinical phenotype.