Dietary Flaxseed Mitigates Impaired Skeletal Muscle Regeneration: in Vivo, in Vitro and in Silico Studies

Promoting and accelerating muscle regeneration through cell therapy in a mouse model

Objectives

Skeletal muscle injuries and disorders are universal clinical challenges with direct and indirect mechanisms and notable residual effects, such as prolonged, intense pain and physical disability. Stem cells, an innovative tool for cell therapy for musculoskeletal disorders, specifically promote skeletal muscle regeneration. This study was aimed at investigating the use of mesenchymal stem cells (MSCs) and their differentiated myocytes as a cell-based therapy to promote regeneration in damaged or diseased skeletal muscle.

Methods

Bone marrow mesenchymal stem cells (BM-MSCs) were isolated from the bone marrow of adult mice and grown in tissue culture flasks. The BM-MSCs were positive for CD90 and CD105, and negative for CD45 and CD34. These cells were induced with specific differentiation medium in vitro to differentiate into a skeletal muscle cell lineage over 7 days. Skeletal muscle differentiation was characterized according to morphology through hematoxylin and eosin staining, and scanning electron microscopy. Immunostaining for Myf-6, myosin heavy chain (MHC), and desmin-specific factors for skeletal muscle development-was performed to confirm skeletal muscle differentiation. An in vivo study in a muscle injury model was used to evaluate cell therapy based on naïve stem cells and differentiated myocytes.

Results

Cultured mouse BM-MSCS were positive for CD90 and CD105, and negative for CD45 and CD34. These cells developed into skeletal muscle with strong skeletal muscle differentiation potential, as confirmed by immunohistochemistry for the markers Myf6, MHC, and desmin. The differentiated myocytes showed better repair enhancement than undifferentiated stem cells after transplantations into a mouse model of skeletal muscle atrophy.

Conclusions

Myocytes derived from BM-MSCs may be incorporated into muscular atrophy treatment as a biological strategy for managing skeletal muscle diseases and injuries, thus advancing cell-based clinical treatments.

Fat infiltration in skeletal muscle: Influential triggers and regulatory mechanism

Fat infiltration in skeletal muscle (also known as myosteatosis) is now recognized as a distinct disease from sarcopenia and is directly related to declining muscle capacity. Hence, understanding the origins and regulatory mechanisms of fat infiltration is vital for maintaining skeletal muscle development and improving human health. In this article, we summarized the triggering factors such as aging, metabolic diseases and metabolic syndromes, nonmetabolic diseases, and muscle injury that all induce fat infiltration in skeletal muscle. We discussed recent advances on the cellular origins of fat infiltration and found several cell types including myogenic cells and non-myogenic cells that contribute to myosteatosis. Furthermore, we reviewed the molecular regulatory mechanism, detection methods, and intervention strategies of fat infiltration in skeletal muscle. Based on the current findings, our review will provide new insight into regulating function and lipid metabolism of skeletal muscle and treating muscle-related diseases.

Alleviative effects of α-lipoic acid on muscle atrophy via the modulation of TNF-α/JNK and PI3K/AKT pathways in high-fat diet and streptozotocin-induced type 2 diabetic rats

Diabetes mellitus (DM) is often accompanied by clinical complications such as sarcopenia. Previous studies have indicated that oxidative stress and insulin resistance (IR) are highly associated with the pathogenesis of diabetic myopathy. α-lipoic acid (ALA), a potent biological antioxidant, exists abundantly in a variety of plants and vegetables. This study aimed to investigate the ameliorative effect of ALA on muscle atrophy in type 2 diabetic rats induced by high-fat diet feeding (HFD) plus streptozotocin (STZ) injection. The HFD/STZ-induced diabetic rats were orally administered 50, 100, or 200 mg/kg body weight ALA once a day for 13 weeks. The results showed that ALA at the tested concentrations significantly increased the soleus muscle mass and muscle fibers in diabetic rats. Proinflammatory cytokines, such as tumor necrosis factor (TNF)-α, were found to decrease in both the serum and muscle of ALA-treated diabetic rats. ALA significantly reduced the protein-expression levels of phosphorylated c-Jun N-terminal kinase (pJNK)/JNK, forkhead box O3 (FOXO3), and muscle ring-finger protein-1 (Murf1); whereas, it enhanced the protein-expression levels of phosphoinositide 3-kinase (PI3K), phosphorylated protein kinase B (pAKT)/AKT, myogenin determination gene D (MyoD), the mechanistic target of rapamycin (mTOR), and myosin heavy chain (MyHC) in the soleus muscle of diabetic rats. The results from this study suggested that ALA treatment may preserve soleus muscle mass, alleviate muscle atrophy by suppressing the TNF-α/JNK pathway, and ameliorate the PI3K/AKT pathway in HFD/STZ-induced type 2 diabetic rats.

Phytochemicals: A potential therapeutic intervention for the prevention and treatment of cachexia

Cachexia, a multifactorial and often irreversible wasting syndrome, is often associated with the final phase of several chronic disorders. Although cachexia is characterized by skeletal muscle wasting and adipose tissue loss, it is a syndrome affecting different organs, which ultimately results in systemic complications and impaired quality of life. The pathogenesis and underlying molecular mechanisms of cachexia are not fully understood, and currently there are no effective standard treatments or approved drug therapies to completely reverse cachexia. Moreover, adequate nutritional interventions alone cannot significantly improve cachexia. Other approaches to ameliorate cachexia are urgently needed, and thus, the role of medicinal plants has received considerable importance in this respect due to their beneficial health properties. Increasing evidence indicates great potential of medicinal plants and their phytochemicals as an alternative and promising treatment strategy to reduce the symptoms of many diseases including cachexia. This article reviews the current status of cachexia, the molecular mechanisms of primary events driving cachexia, and state-of-the-art knowledge that reports the preventive and therapeutic activities of multiple families of phytochemical compounds and their pharmacological mode of action, which may hold promise as an alternative treatment modality for the management of cachexia. Based on our review of various in vitro and in vivo models of cachexia, we would conclude that phytochemicals may have therapeutic potential to attenuate cachexia, although clinical trials are required to unequivocally confirm this premise.

Functional Nutrients to Ameliorate Neurogenic Muscle Atrophy

Neurogenic muscle atrophy is a debilitating condition that occurs from nerve trauma in association with diseases or during aging, leading to reduced interaction between motoneurons and skeletal fibers. Current therapeutic approaches aiming at preserving muscle mass in a scenario of decreased nervous input include physical activity and employment of drugs that slow down the progression of the condition yet provide no concrete resolution. Nutritional support appears as a precious tool, adding to the success of personalized medicine, and could thus play a relevant part in mitigating neurogenic muscle atrophy. We herein summarize the molecular pathways triggered by denervation of the skeletal muscle that could be affected by functional nutrients. In this narrative review, we examine and discuss studies pertaining to the use of functional ingredients to counteract neurogenic muscle atrophy, focusing on their preventive or curative means of action within the skeletal muscle. We reviewed experimental models of denervation in rodents and in amyotrophic lateral sclerosis, as well as that caused by aging, considering the knowledge generated with use of animal experimental models and, also, from human studies.

Disease-associated metabolic alterations that impact satellite cells and muscle regeneration: perspectives and therapeutic outlook

Many chronic disease patients experience a concurrent loss of lean muscle mass. Skeletal muscle is a dynamic tissue maintained by continuous protein turnover and progenitor cell activity. Muscle stem cells, or satellite cells, differentiate (by a process called myogenesis) and fuse to repair and regenerate muscle. During myogenesis, satellite cells undergo extensive metabolic alterations; therefore, pathologies characterized by metabolic derangements have the potential to impair myogenesis, and consequently exacerbate skeletal muscle wasting. How disease-associated metabolic disruptions in satellite cells might be contributing to wasting is an important question that is largely neglected. With this review we highlight the impact of various metabolic disruptions in disease on myogenesis and skeletal muscle regeneration. We also discuss metabolic therapies with the potential to improve myogenesis, skeletal muscle regeneration, and ultimately muscle mass.

Dietary α-Linolenic Acid Counters Cardioprotective Dysfunction in Diabetic Mice: Unconventional PUFA Protection

Whether dietary omega-3 (n-3) polyunsaturated fatty acid (PUFA) confers cardiac benefit in cardiometabolic disorders is unclear. We test whether dietary -linolenic acid (ALA) enhances myocardial resistance to ischemia-reperfusion (I-R) and responses to ischemic preconditioning (IPC) in type 2 diabetes (T2D); and involvement of conventional PUFA-dependent mechanisms (caveolins/cavins, kinase signaling, mitochondrial function, and inflammation). Eight-week male C57Bl/6 mice received streptozotocin (75 mg/kg) and 21 weeks high-fat/high-carbohydrate feeding. Half received ALA over six weeks. Responses to I-R/IPC were assessed in perfused hearts. Localization and expression of caveolins/cavins, protein kinase B (AKT), and glycogen synthase kinase-3 β (GSK3β); mitochondrial function; and inflammatory mediators were assessed. ALA reduced circulating leptin, without affecting body weight, glycemic dysfunction, or cholesterol. While I-R tolerance was unaltered, paradoxical injury with IPC was reversed to cardioprotection with ALA. However, post-ischemic apoptosis (nucleosome content) appeared unchanged. Benefit was not associated with shifts in localization or expression of caveolins/cavins, p-AKT, p-GSK3β, or mitochondrial function. Despite mixed inflammatory mediator changes, tumor necrosis factor-a (TNF-a) was markedly reduced. Data collectively reveal a novel impact of ALA on cardioprotective dysfunction in T2D mice, unrelated to caveolins/cavins, mitochondrial, or stress kinase modulation. Although evidence suggests inflammatory involvement, the basis of this "un-conventional" protection remains to be identified.

Cardiomyoblast caveolin expression: effects of simulated diabetes, α-linolenic acid, and cell signaling pathways

Caveolins regulate myocardial substrate handling, survival signaling, and stress resistance; however, control of expression is incompletely defined. We test how metabolic features of type 2 diabetes (T2D), and modulation of cell signaling, influence caveolins in H9c2 cardiomyoblasts. Cells were exposed to glucose (25 vs. 5 mM), insulin (100 nM), or palmitate (0.1 mM), individually or combined, and the effects of adenylate cyclase (AC) activation (50 μM forskolin), focal adhesion kinase (FAK) or protein kinase C β2 (PKCβ2) inhibition (1 μM FAK inhibitor 14 or CGP-53353, respectively) or the polyunsaturated fatty acid (PUFA) α-linolenic acid (ALA; 10 μM) were tested. Simulated T2D (elevated glucose + insulin + palmitate) depressed caveolin-1 and -3 without modifying caveolin-2. Caveolin-3 repression was primarily palmitate dependent, whereas high glucose (HG) and insulin independently increased caveolin-3 (while reducing expression when combined). Differential control was evident: baseline caveolin-3 was suppressed by FAK/PKCβ2 and insensitive to AC activities, with baseline caveolin-1 and -2 suppressed by AC and insensitive to FAK/PKCβ2. Forskolin and ALA selectively preserved caveolin-3 in T2D cells, whereas PKCβ2 and FAK inhibition increased caveolin-3 under all conditions. Despite preservation of caveolin-3, ALA did not modify nucleosome content (apoptosis marker) or transcription of proinflammatory mediators in T2D cells. In summary, caveolin-1 and -3 are strongly repressed with simulated T2D, with caveolin-3 particularly sensitive to palmitate; intrinsic PKCβ2 and FAK activities depress caveolin-3 in healthy and stressed cells; ALA and AC activation and PKCβ2 inhibition preserve caveolin-3 under T2D conditions; and caveolin-3 changes with T2D and ALA appear unrelated to inflammatory signaling or extent of apoptosis.

Displaced Myonuclei in Cancer Cachexia Suggest Altered Innervation

An idiopathic myopathy characterized by central nuclei in muscle fibers, a hallmark of muscle regeneration, has been observed in cancer patients. In cancer cachexia skeletal muscle is incapable of regeneration, consequently, this observation remains unaccounted for. In C26-tumor bearing, cachectic mice, we observed muscle fibers with central nuclei in the absence of molecular markers of bona fide regeneration. These clustered, non-peripheral nuclei were present in NCAM-expressing muscle fibers. Since NCAM expression is upregulated in denervated myofibers, we searched for additional makers of denervation, including AchRs, MUSK, and HDAC. This last one being also consistently upregulated in cachectic muscles, correlated with an increase of central myonuclei. This held true in the musculature of patients suffering from gastrointestinal cancer, where a progressive increase in the number of central myonuclei was observed in weight stable and in cachectic patients, compared to healthy subjects. Based on all of the above, the presence of central myonuclei in cancer patients and animal models of cachexia is consistent with motor neuron loss or NMJ perturbation and could underlie a previously neglected phenomenon of denervation, rather than representing myofiber damage and regeneration in cachexia. Similarly to aging, denervation-dependent myofiber atrophy could contribute to muscle wasting in cancer cachexia.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

What Can be Learned from the Time Course of Changes in Low-Frequency Stimulated Muscle?

Not available.

2017Spring PaduaMuscleDays, roots and byproducts

The second 2017 issue of EJTM volume 27 contains the collection of abstracts from the 2017Spring PaduaMuscleDays conference, that was held March 23-25 in Montegrotto, Euganei Hills, Padova, Italy. In addition to a brief history of the Padova Myology Meetings held during the last 30 years, the present and the future of the PaduaMuscleDays conference are discussed with special reference to new media and the options they offer to spread to a larger audience the results of the many workshops held in the Hotel Augustus conference hall and in the Aula Guariento of the Accademia Galileiana di Scienze, Lettere ed Arti, one of the hidden treasures of the medioeval Padua, Italy. Preliminary announcements of the 2017 and 2018 events, in particular of the Giovanni Salviati Memorial, will follow.

α-Linolenic Acid Reduces TNF-Induced Apoptosis in C2C12 Myoblasts by Regulating Expression of Apoptotic Proteins

Impaired regeneration and consequent muscle wasting is a major feature of muscle degenerative diseases. Nutritional interventions such as adjuvant strategy for preventing these conditions are recently gaining increasing attention. Ingestion of n3-polyunsaturated fatty acids has been suggested as having a positive impact on muscle diseases. We recently demonstrated that a diet enriched with plant derived n3-fatty acid, α-linolenic acid (ALA), exerts potent beneficial effects in preserving skeletal muscle regeneration in models of muscle dystrophy. To better elucidate the underlying mechanism we here investigate on the expression level of the anti- and pro-apoptotic proteins, as well as caspase-3 activity, in C2C12 myoblasts challenged with pathological levels of tumor necrosis factor-α (TNF). The results demonstrated that ALA protective effect on C2C12 myoblasts was associated with a decrease in caspase-3 activity and an increase of the Bcl-2/Bax ratio. Indeed, the effect of ALA was directed to rescuing Bcl-2 expression and to revert Bax translocation to mitochondria both affected in an opposite way by TNF, a major pro-inflammatory cytokine expressed in damaged skeletal muscle. Therefore, ALA counteracts inflammatory signals in the muscle microenvironment and may represent a valuable strategy for ameliorating skeletal muscle pathologies.

How Diet Intervention via Modulation of DNA Damage Response through MicroRNAs May Have an Effect on Cancer Prevention and Aging, an in Silico Study

The DNA damage response (DDR) is a molecular mechanism that cells have evolved to sense DNA damage (DD) to promote DNA repair, or to lead to apoptosis, or cellular senescence if the damage is too extensive. Recent evidence indicates that microRNAs (miRs) play a critical role in the regulation of DDR. Dietary bioactive compounds through miRs may affect activity of numerous genes. Among the most studied bioactive compounds modulating expression of miRs are epi-gallocatechin-3-gallate, curcumin, resveratrol and n3-polyunsaturated fatty acids. To compare the impact of these dietary compounds on DD/DDR network modulation, we performed a literature search and an in silico analysis by the DIANA-mirPathv3 software. The in silico analysis allowed us to identify pathways shared by different miRs involved in DD/DDR vis-à-vis the specific compounds. The results demonstrate that certain miRs (e.g., -146, -21) play a central role in the interplay among DD/DDR and the bioactive compounds. Furthermore, some specific pathways, such as "fatty acids biosynthesis/metabolism", "extracellular matrix-receptor interaction" and "signaling regulating the pluripotency of stem cells", appear to be targeted by most miRs affected by the studied compounds. Since DD/DDR and these pathways are strongly related to aging and carcinogenesis, the present in silico results of our study suggest that monitoring the induction of specific miRs may provide the means to assess the antiaging and chemopreventive properties of particular dietary compounds.