Mustn1 is a smooth muscle cell-secreted microprotein that modulates skeletal muscle extracellular matrix composition

OBJECTIVE

Skeletal muscle plasticity and remodeling are critical for adapting tissue function to use, disuse, and regeneration. The aim of this study was to identify genes and molecular pathways that regulate the transition from atrophy to compensatory hypertrophy or recovery from injury. Here, we have used a mouse model of hindlimb unloading and reloading, which causes skeletal muscle atrophy, and compensatory regeneration and hypertrophy, respectively.

METHODS

We analyzed mouse skeletal muscle at the transition from hindlimb unloading to reloading for changes in transcriptome and extracellular fluid proteome. We then used qRT-PCR, immunohistochemistry, and bulk and single-cell RNA sequencing data to determine Mustn1 gene and protein expression, including changes in gene expression in mouse and human skeletal muscle with different challenges such as exercise and muscle injury. We generated Mustn1-deficient genetic mouse models and characterized them in vivo and ex vivo with regard to muscle function and whole-body metabolism. We isolated smooth muscle cells and functionally characterized them, and performed transcriptomics and proteomics analysis of skeletal muscle and aorta of Mustn1-deficient mice.

RESULTS

We show that Mustn1 (Musculoskeletal embryonic nuclear protein 1, also known as Mustang) is highly expressed in skeletal muscle during the early stages of hindlimb reloading. Mustn1 expression is transiently elevated in mouse and human skeletal muscle in response to intense exercise, resistance exercise, or injury. We find that Mustn1 expression is highest in smooth muscle-rich tissues, followed by skeletal muscle fibers. Muscle from heterozygous Mustn1-deficient mice exhibit differences in gene expression related to extracellular matrix and cell adhesion, compared to wild-type littermates. Mustn1-deficient mice have normal muscle and aorta function and whole-body glucose metabolism. We show that Mustn1 is secreted from smooth muscle cells, and that it is present in arterioles of the muscle microvasculature and in muscle extracellular fluid, particularly during the hindlimb reloading phase. Proteomics analysis of muscle from Mustn1-deficient mice confirms differences in extracellular matrix composition, and female mice display higher collagen content after chemically induced muscle injury compared to wild-type littermates.

CONCLUSIONS

We show that, in addition to its previously reported intracellular localization, Mustn1 is a microprotein secreted from smooth muscle cells into the muscle extracellular space. We explore its role in muscle ECM deposition and remodeling in homeostasis and upon muscle injury. The role of Mustn1 in fibrosis and immune infiltration upon muscle injury and dystrophies remains to be investigated, as does its potential for therapeutic interventions.

Zfp697 is an RNA-binding protein that regulates skeletal muscle inflammation and regeneration

Muscular atrophy is a mortality risk factor that happens with disuse, chronic disease, and aging. Recovery from atrophy requires changes in several cell types including muscle fibers, and satellite and immune cells. Here we show that Zfp697/ZNF697 is a damage-induced regulator of muscle regeneration, during which its expression is transiently elevated. Conversely, sustained Zfp697 expression in mouse muscle leads to a gene expression signature of chemokine secretion, immune cell recruitment, and extracellular matrix remodeling. Myofiber-specific Zfp697 ablation hinders the inflammatory and regenerative response to muscle injury, compromising functional recovery. We uncover Zfp697 as an essential interferon gamma mediator in muscle cells, interacting primarily with ncRNAs such as the pro-regenerative miR-206. In sum, we identify Zfp697 as an integrator of cell-cell communication necessary for tissue regeneration.

Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity

Endurance exercise promotes skeletal muscle vascularization, oxidative metabolism, fiber-type switching, and neuromuscular junction integrity. Importantly, the metabolic and contractile properties of the muscle fiber must be coupled to the identity of the innervating motor neuron (MN). Here, we show that muscle-derived neurturin (NRTN) acts on muscle fibers and MNs to couple their characteristics. Using a muscle-specific NRTN transgenic mouse (HSA-NRTN) and RNA sequencing of MN somas, we observed that retrograde NRTN signaling promotes a shift toward a slow MN identity. In muscle, NRTN increased capillary density and oxidative capacity and induced a transcriptional reprograming favoring fatty acid metabolism over glycolysis. This combination of effects on muscle and MNs makes HSA-NRTN mice lean with remarkable exercise performance and motor coordination. Interestingly, HSA-NRTN mice largely recapitulate the phenotype of mice with muscle-specific expression of its upstream regulator PGC-1ɑ1. This work identifies NRTN as a myokine that couples muscle oxidative capacity to slow MN identity.

Effects of Tryptophan Supplementation and Exercise on the Fate of Kynurenine Metabolites in Mice and Humans

The kynurenine pathway of tryptophan (TRP) degradation (KP) generates metabolites with effects on metabolism, immunity, and mental health. Endurance exercise training can change KP metabolites by changing the levels of KP enzymes in skeletal muscle. This leads to a metabolite pattern that favors energy expenditure and an anti-inflammatory immune cell profile and reduces neurotoxic metabolites. Here, we aimed to understand if TRP supplementation in untrained vs. trained subjects affects KP metabolite levels and biological effects. Our data show that chronic TRP supplementation in mice increases all KP metabolites in circulation, and that exercise reduces the neurotoxic branch of the pathway. However, in addition to increasing wheel running, we did not observe other effects of TRP supplementation on training adaptations, energy metabolism or behavior in mice. A similar increase in KP metabolites was seen in trained vs. untrained human volunteers that took a TRP drink while performing a bout of aerobic exercise. With this acute TRP administration, TRP and KYN were higher in the trained vs. the untrained group. Considering the many biological effects of the KP, which can lead to beneficial or deleterious effects to health, our data encourage future studies of the crosstalk between TRP supplementation and physical exercise.

Use of the socio-ecological model to explore factors that influence the implementation of a diabetes structured education programme (EXTEND project) inLilongwe, Malawi and Maputo, Mozambique: a qualitative study

BACKGROUND

Diabetes Self-Management Education and Support (DSMES) programmes are vital for type 2 diabetes mellitus (T2DM) management. However, they are limited in Sub-Saharan Africa (SSA). To address this gap, a DSMES, namedEXTEND was developed in Lilongwe (Malawi) and Maputo (Mozambique). This qualitative study aimed to explore factors that influence the implementation of DSMES in these settings.

METHODS

The Socio-ecological model was applied to explore factors influencing the implementation of DSMES in SSA. Data was analysed using the Framework method and constant comparative techniques. Sixty-six people participated in the study: people with T2DM who participated in the EXTEND programme; healthcare professionals (HCPs), EXTEND educators, EXTEND trainers, and stakeholders.

RESULTS

Our findings indicate that there is a need to develop an integrated and dedicated diabetes services in SSA healthcare systems, incorporating culturally adapted DSMES and tailored diabetes training to all professions involved in diabetes management. Traditional media and the involvement of community leaders were proposed as important elements to help engage and promote DSMES programmes in local communities. During the design and implementation of DSMES, it is important to consider individual and societal barriers to self-care.

CONCLUSION

Findings from this study suggest that multi-faceted factors play a significant role to the implementation of DSMES programmes in LICs. In the future, EXTEND could be incorporated in the development of diabetes training and dedicated diabetes services in SSA healthcare systems, acting as an educational tool for both people with T2DM and HCPs. This project was supported by the Medical Research Council GCRF NCDs Foundation Awards 2016 Development Pathway Funding.

Effects of topological constraints on the alignment and maturation of multinucleated myotubes

Microfluidic-based technologies enable the development of cell culture systems that provide tailored microenvironmental inputs to mammalian cells. Primary myoblasts can be induced to differentiate into multinucleated skeletal muscle cells, myotubes, which are a relevant model system for investigating skeletal muscle metabolism and physiology in vitro. However, it remains challenging to differentiate primary myoblasts into mature myotubes in microfluidics devices. Here we investigated the effects of integrating continuous (solid) and intermittent (dashed) walls in microfluidic channels as topological constraints in devices designed to promote the alignment and maturation of primary myoblast-derived myotubes. The topological constraints caused alignment of the differentiated myotubes, mimicking the native anisotropic organization of skeletal muscle cells. Interestingly, dashed walls facilitated the maturation of skeletal muscle cells, as measured by quantifying myotube cell area and the number of nuclei per myotube. Together, our results suggest that integrating dashed walls as topographic constraints in microfluidic devices supports the alignment and maturation of primary myoblast-derived myotubes.

[A double pandemic : the impact of anti-Covid measures on obesity]

To deal with the COVID-19 pandemic, several restrictive measures have been put in place that cause significant disruption to lifestyle habits. We conducted a review of the literature to study the impact of these changes on the body weight of populations. We observed changes in eating habits (increase in the number of snacks and consumption of sugary products), a decrease in physical activity and an increase in stress that can exacerbate eating disorders. Increased efforts must be made to support patients during this difficult time, including public health measures to counteract these behaviours in order to prevent health complications.

[The role of stress in obesity]

Stress is known to favour weight gain. This can be explained by various physiopathological and behavioural mechanisms. Specifically, chronic stress induces a dysfunction of the sympathetic nervous system and of the hypothalamic-pituitary-adrenal axis which favours obesity, and the other way around. Furthermore, stress promotes eating disorders and a decrease in physical activity. Various studies using strategies that act specifically on stress have shown benefits in terms of weight loss. It is therefore important to evaluate stress in any patient suffering from obesity and to propose a treatment adapted to the patient's needs.

The process of building the priority of neglected tropical diseases: A global policy analysis

The global burden attributed to Neglected Tropical Diseases (NTDs) is 47.9 million Disability-Adjusted Life Years (DALYs). These diseases predominantly affect disadvantaged populations. Priority for NTDs has grown in recent years, which is observed by their inclusion in the sustainable development goals (SDGs). This study analyzed the process that allowed these diseases to be included on the global health policy agenda. This global policy analysis used the Shiffman and Smith framework to understand the determinants of global health political priority for NTDs. The framework comprises four categories: actor power, ideas, political contexts, and issue characteristics. Global documents and World Health Assembly (WHA) resolutions were examined, key-informant interviews were conducted, and academic publications were reviewed to understand the four categories that comprise the framework. A total of 37 global policy documents, 15 WHA resolutions, and 38 academic publications were examined. Twelve semi-structured interviews were conducted with individuals representing different sectors within the NTD community who have been involved in raising the priority of these diseases. This study found that several factors helped better position NTDs in the global health agenda. These include the leadership of actors that mobilized the global health community, the creation of a label combining these diseases as a group to represent a larger disease burden, the presence of mechanisms aligning the NTD community, and the agreement on ways to present the NTD burden and potential solutions. The process of building the priority of NTDs in the global health agenda shows that several determinants led to positive outcomes, but these diseases continue to have low priority at the global level which requires the implementation of actions to increase their global priority. These include sustaining the commitment of current actors and engaging new ones; increasing the attention given to diseases formerly categorized as "tool-deficient", including zoonotic NTDs; continue leveraging on policy windows and creating favorable policy moments to sustain commitment, as well as setting realistic targets. Findings from this study can help develop strategies to build the momentum and drive actions to implement the goals of the new Roadmap for NTDs in the pathway to universal health coverage (UHC) and sustainable development.

Position Statement on Atopic Dermatitis in Sub-Saharan Africa: current status and roadmap

BACKGROUND

The first International Society of Atopic Dermatitis (ISAD) global meeting dedicated to atopic dermatitis (AD) in Sub-Saharan Africa (SSA) was held in Geneva, Switzerland in April 2019. A total of 30 participants were present at the meeting, including those from 17 SSA countries, representatives of the World Health Organization (WHO), the International Foundation for Dermatology (IFD) (a committee of the International League of Dermatological Societies, ILDS www.ilds.org), the Fondation pour la Dermatite Atopique, as well as specialists in telemedicine, artificial intelligence and therapeutic patient education (TPE).

RESULTS

AD is one of the most prevalent chronic inflammatory skin diseases in SSA. Besides neglected tropical diseases (NTDs) with a dermatological presentation, AD requires closer attention from the WHO and national Departments of Health.

CONCLUSIONS

A roadmap has been defined with top priorities such as access to essential medicines and devices for AD care, in particular emollients, better education of primary healthcare workers for adequate triage (e.g. better educational materials for skin diseases in pigmented skin generally and AD in particular, especially targeted to Africa), involvement of traditional healers and to a certain extent also patient education, bearing in mind the barriers to effective healthcare faced in SSA countries such as travel distances to health facilities, limited resources and the lack of dermatological expertise. In addition, several initiatives concerning AD research in SSA were discussed and should be implemented in close collaboration with the WHO and assessed at follow-up meetings, in particular, at the next ISAD meeting in Seoul, South Korea and African Society of Dermatology and Venereology (ASDV) meeting in Nairobi, Kenya, both in 2020.

[Obesity : eat less and move more ? Not so easy]

Obesity is a chronic disease that requires a complex treatment. Establishing a balanced diet and regular physical activity is not always simple, especially in the long term. There are multiple factors (biological and psychological) favoring weight gain, often limiting the effectiveness of lifestyle approaches. Pharmacology offers us another therapeutic option with new molecules effective for weight loss. Bariatric surgery is also effective, but it is not without risks, especially if the patients have not been adequately prepared for this procedure. Furthermore, these approaches should always be proposed as complementary to lifestyle changes. This article summarizes the different treatments for obesity and highlights the importance of a multidisciplinary management and proper patient education.

PGC-1α isoforms coordinate to balance hepatic metabolism and apoptosis in inflammatory environments

Objective

The liver is regularly exposed to changing metabolic and inflammatory environments. It must sense and adapt to metabolic need while balancing resources required to protect itself from insult. Peroxisome proliferator activated receptor gamma coactivator-1 alpha (PGC-1α) is a transcriptional coactivator expressed as multiple, alternatively spliced variants transcribed from different promoters that coordinate metabolic adaptation and protect against inflammation. It is not known how PGC-1α integrates extracellular signals to balance metabolic and anti-inflammatory outcomes.

Methods

Primary mouse hepatocytes were used to evaluate the role(s) of different PGC-1α proteins in regulating hepatic metabolism and inflammatory signaling downstream of tumor necrosis factor alpha (TNFα). Gene expression and signaling analysis were combined with biochemical measurement of apoptosis using gain- and loss-of-function in vitro and in vivo.

Results

Hepatocytes expressed multiple isoforms of PGC-1α, including PGC-1α4, which microarray analysis showed had common and isoform-specific functions linked to metabolism and inflammation compared with canonical PGC-1α1. Whereas PGC-1α1 primarily impacted gene programs of nutrient metabolism and mitochondrial biology, TNFα signaling showed several pathways related to innate immunity and cell death downstream of PGC-1α4. Gain- and loss-of-function models illustrated that PGC-1α4 uniquely enhanced expression of anti-apoptotic gene programs and attenuated hepatocyte apoptosis in response to TNFα or lipopolysaccharide (LPS). This was in contrast to PGC-1α1, which decreased the expression of a wide inflammatory gene network but did not prevent hepatocyte death in response to cytokines.

Conclusions

PGC-1α variants have distinct, yet complementary roles in hepatic responses to metabolism and inflammation, and we identify PGC-1α4 as an important mitigator of apoptosis.

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Multiple isoforms of PGC-1α are expressed in hepatocytes, including PGC-1α4.

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PGC-1α1 and PGC-1α4 share many metabolic targets, but PGC-1α4 has unique functions linked to hepatic inflammatory signalling.

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PGC-1α4 attenuates hepatocyte apoptosis in response to TNFα and LPS in vitro and in vivo.

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Inflammatory signaling influences PGC-1α4 localization in hepatocytes.

LIM and cysteine-rich domains 1 (LMCD1) regulates skeletal muscle hypertrophy, calcium handling, and force

BACKGROUND

Skeletal muscle mass and strength are crucial determinants of health. Muscle mass loss is associated with weakness, fatigue, and insulin resistance. In fact, it is predicted that controlling muscle atrophy can reduce morbidity and mortality associated with diseases such as cancer cachexia and sarcopenia.

METHODS

We analyzed gene expression data from muscle of mice or human patients with diverse muscle pathologies and identified LMCD1 as a gene strongly associated with skeletal muscle function. We transiently expressed or silenced LMCD1 in mouse gastrocnemius muscle or in mouse primary muscle cells and determined muscle/cell size, targeted gene expression, kinase activity with kinase arrays, protein immunoblotting, and protein synthesis levels. To evaluate force, calcium handling, and fatigue, we transduced the flexor digitorum brevis muscle with a LMCD1-expressing adenovirus and measured specific force and sarcoplasmic reticulum Ca²⁺ release in individual fibers. Finally, to explore the relationship between LMCD1 and calcineurin, we ectopically expressed Lmcd1 in the gastrocnemius muscle and treated those mice with cyclosporine A (calcineurin inhibitor). In addition, we used a luciferase reporter construct containing the myoregulin gene promoter to confirm the role of a LMCD1-calcineurin-myoregulin axis in skeletal muscle mass control and calcium handling.

RESULTS

Here, we identify LIM and cysteine-rich domains 1 (LMCD1) as a positive regulator of muscle mass, that increases muscle protein synthesis and fiber size. LMCD1 expression in vivo was sufficient to increase specific force with lower requirement for calcium handling and to reduce muscle fatigue. Conversely, silencing LMCD1 expression impairs calcium handling and force, and induces muscle fatigue without overt atrophy. The actions of LMCD1 were dependent on calcineurin, as its inhibition using cyclosporine A reverted the observed hypertrophic phenotype. Finally, we determined that LMCD1 represses the expression of myoregulin, a known negative regulator of muscle performance. Interestingly, we observed that skeletal muscle LMCD1 expression is reduced in patients with skeletal muscle disease.

CONCLUSIONS

Our gain- and loss-of-function studies show that LMCD1 controls protein synthesis, muscle fiber size, specific force, Ca²⁺ handling, and fatigue resistance. This work uncovers a novel role for LMCD1 in the regulation of skeletal muscle mass and function with potential therapeutic implications.

The process of prioritization of non-communicable diseases in the global health policy arena

Although non-communicable diseases (NCDs) are the leading cause of morbidity and mortality worldwide, the global policy response has not been commensurate with their health, economic and social burden. This study examined factors facilitating and hampering the prioritization of NCDs on the United Nations (UN) health agenda. Shiffman and Smith's (Generation of political priority for global health initiatives: a framework and case study of maternal mortality. The Lancet 370: 1370-9.) political priority framework served as a structure for analysis of a review of NCD policy documents identified through the World Health Organization's (WHO) NCD Global Action Plan 2013-20, and complemented by 11 semi-structured interviews with key informants from different sectors. The results show that a cohesive policy community exists, and leaders are present, however, actor power does not extend beyond the health sector and the role of guiding institutions and civil society have only recently gained momentum. The framing of NCDs as four risk factors and four diseases does not necessarily resonate with experts from the larger policy community, but the economic argument seems to have enabled some traction to be gained. While many policy windows have occurred, their impact has been limited by the institutional constraints of the WHO. Credible indicators and effective interventions exist, but their applicability globally, especially in low- and middle-income countries, is questionable. To be effective, the NCD movement needs to expand beyond global health experts, foster civil society and develop a broader and more inclusive global governance structure. Applying the Shiffman and Smith framework for NCDs enabled different elements of how NCDs were able to get on the UN policy agenda to be disentangled. Much work has been done to frame the challenges and solutions, but implementation processes and their applicability remain challenging globally. NCD responses need to be adapted to local contexts, focus sufficiently on both prevention and management of disease, and have a stronger global governance structure.

Kynurenic Acid and Gpr35 Regulate Adipose Tissue Energy Homeostasis and Inflammation

The role of tryptophan-kynurenine metabolism in psychiatric disease is well established, but remains less explored in peripheral tissues. Exercise training activates kynurenine biotransformation in skeletal muscle, which protects from neuroinflammation and leads to peripheral kynurenic acid accumulation. Here we show that kynurenic acid increases energy utilization by activating G protein-coupled receptor Gpr35, which stimulates lipid metabolism, thermogenic, and anti-inflammatory gene expression in adipose tissue. This suppresses weight gain in animals fed a high-fat diet and improves glucose tolerance. Kynurenic acid and Gpr35 enhance Pgc-1α1 expression and cellular respiration, and increase the levels of Rgs14 in adipocytes, which leads to enhanced beta-adrenergic receptor signaling. Conversely, genetic deletion of Gpr35 causes progressive weight gain and glucose intolerance, and sensitizes to the effects of high-fat diets. Finally, exercise-induced adipose tissue browning is compromised in Gpr35 knockout animals. This work uncovers kynurenine metabolism as a pathway with therapeutic potential to control energy homeostasis.

Small molecule PGC-1α1 protein stabilizers induce adipocyte Ucp1 expression and uncoupled mitochondrial respiration

Objective

The peroxisome proliferator-activated receptor-γ coactivator-1α1 (PGC-1α1) regulates genes involved in energy metabolism. Increasing adipose tissue energy expenditure through PGC-1α1 activation is potentially beneficial for systemic metabolism. Pharmacological PGC-1α1 activators could be valuable tools in the fight against obesity and metabolic disease. Finding such compounds has been challenging partly because PGC-1α1 is a transcriptional coactivator with no known ligand-binding properties. While, PGC-1α1 activation is regulated by several mechanisms, protein stabilization is a crucial limiting step due to its short half-life under unstimulated conditions.

Methods

We designed a cell-based high-throughput screening system to identify PGC-1α1 protein stabilizers. Positive hits were tested for their ability to induce endogenous PGC-1α1 protein accumulation and activate target gene expression in brown adipocytes. Select compounds were analyzed for their effects on global gene expression and cellular respiration in adipocytes.

Results

Among 7,040 compounds screened, we highlight four small molecules with high activity as measured by: PGC-1α1 protein accumulation, target gene expression, and uncoupled mitochondrial respiration in brown adipocytes.

Conclusions

We identify compounds that induce PGC-1α1 protein accumulation and show that this increases uncoupled respiration in brown adipocytes. This screening platform establishes the foundation for a new class of therapeutics with potential use in obesity and associated disorders.

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A high-throughput platform to identify PGC-1α1 activators.

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PGC-1α1 protein stabilizers work as activators in brown adipocytes.

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Small molecule PGC-1α1 activators induce Ucp1 expression and cellular respiration.

Human Carboxylesterase 2 Reverses Obesity-Induced Diacylglycerol Accumulation and Glucose Intolerance

Serine hydrolases are a large family of multifunctional enzymes known to influence obesity. Here, we performed activity-based protein profiling to assess the functional level of serine hydrolases in liver biopsies from lean and obese humans in order to gain mechanistic insight into the pathophysiology of metabolic disease. We identified reduced hepatic activity of carboxylesterase 2 (CES2) and arylacetamide deacetylase (AADAC) in human obesity. In primary human hepatocytes, CES2 knockdown impaired glucose storage and lipid oxidation. In mice, obesity reduced CES2, whereas adenoviral delivery of human CES2 reversed hepatic steatosis, improved glucose tolerance, and decreased inflammation. Lipidomic analysis identified a network of CES2-regulated lipids altered in human and mouse obesity. CES2 possesses triglyceride and diacylglycerol lipase activities and displayed an inverse correlation with HOMA-IR and hepatic diacylglycerol concentrations in humans. Thus, decreased CES2 is a conserved feature of obesity and plays a causative role in the pathogenesis of obesity-related metabolic disturbances.

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Obesity decreases hepatic activity of AADAC and CES2 in humans

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CES2 depletion impairs lipid and glucose metabolism in primary human hepatocytes

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Human CES2 expression reverses hepatic steatosis and glucose intolerance in mice

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CES2 controls a hepatic lipid network dysregulated in human and mouse obesity

Neurturin is a PGC-1α1-controlled myokine that promotes motor neuron recruitment and neuromuscular junction formation

OBJECTIVE

We examined whether skeletal muscle overexpression of PGC-1α1 or PGC-1α4 affected myokine secretion and neuromuscular junction (NMJ) formation.

METHODS

A microfluidic device was used to model endocrine signaling and NMJ formation between primary mouse myoblast-derived myotubes and embryonic stem cell-derived motor neurons. Differences in hydrostatic pressure allowed for fluidic isolation of either cell type or unidirectional signaling in the fluid phase. Myotubes were transduced to overexpress PGC-1α1 or PGC-1α4, and myokine secretion was quantified using a proximity extension assay. Morphological and functional changes in NMJs were measured by fluorescent microscopy and by monitoring muscle contraction upon motor neuron stimulation.

RESULTS

Skeletal muscle transduction with PGC-1α1, but not PGC-1α4, increased NMJ formation and size. PGC-1α1 increased muscle secretion of neurturin, which was sufficient and necessary for the effects of muscle PGC-1α1 on NMJ formation.

CONCLUSIONS

Our findings indicate that neurturin is a mediator of PGC-1α1-dependent retrograde signaling from muscle to motor neurons.

The role of epigenetic modifiers in extended cultures of functional hepatocyte-like cells derived from human neonatal mesenchymal stem cells

The development of predictive in vitro stem cell-derived hepatic models for toxicological drug screening is an increasingly important topic. Herein, umbilical cord tissue-derived mesenchymal stem cells (hnMSCs) underwent hepatic differentiation using an optimized three-step core protocol of 24 days that mimicked liver embryogenesis with further exposure to epigenetic markers, namely the histone deacetylase inhibitor trichostatin A (TSA), the cytidine analogue 5-azacytidine (5-AZA) and dimethyl sulfoxide (DMSO). FGF-2 and FGF-4 were also tested to improve endoderm commitment and foregut induction during Step 1 of the differentiation protocol, being HHEX expression increased with FGF-2 (4 ng/mL). DMSO (1%, v/v) when added at day 10 enhanced cell morphology, glycogen storage ability, enzymatic activity and induction capacity. Moreover, the stability of the hepatic phenotype under the optimized differentiation conditions was examined up to day 34. Our findings showed that hepatocyte-like cells (HLCs) acquired the ability to metabolize glucose, produce albumin and detoxify ammonia. Global transcriptional analysis of the HLCs showed a partial hepatic differentiation degree. Global analysis of gene expression in the different cells revealed shared expression of gene groups between HLCs and human primary hepatocytes (hpHeps) that were not observed between HepG2 and hpHeps. In addition, bioinformatics analysis of gene expression data placed HLCs between the HepG2 cell line and hpHeps and distant from hnMSCs. The enhanced hepatic differentiation observed was supported by the presence of the hepatic drug transporters OATP-C and MRP-2 and gene expression of the hepatic markers CK18, TAT, AFP, ALB, HNF4A and CEBPA; and by their ability to display stable UGT-, EROD-, ECOD-, CYP1A1-, CYP2C9- and CYP3A4-dependent activities at levels either comparable with or even higher than those observed in primary hepatocytes and HepG2 cells. Overall, an improvement of the hepatocyte-like phenotype was achieved for an extended culture time suggesting a role of the epigenetic modifiers in hepatic differentiation and maturation and presenting hnMSC-HLCs as an advantageous alternative for drug discovery and in vitro toxicology testing.

Neuronal cholesterol metabolism increases dendritic outgrowth and synaptic markers via a concerted action of GGTase-I and Trk

Cholesterol 24-hydroxylase (CYP46A1) is responsible for brain cholesterol elimination and therefore plays a crucial role in the control of brain cholesterol homeostasis. Altered CYP46A1 expression has been associated with several neurodegenerative diseases and changes in cognition. Since CYP46A1 activates small guanosine triphosphate-binding proteins (sGTPases), we hypothesized that CYP46A1 might be affecting neuronal development and function by activating tropomyosin-related kinase (Trk) receptors and promoting geranylgeranyl transferase-I (GGTase-I) prenylation activity. Our results show that CYP46A1 triggers an increase in neuronal dendritic outgrowth and dendritic protrusion density, and elicits an increase of synaptic proteins in the crude synaptosomal fraction. Strikingly, all of these effects are abolished by pharmacological inhibition of GGTase-I activity. Furthermore, CYP46A1 increases Trk phosphorylation, its interaction with GGTase-I, and the activity of GGTase-I, which is crucial for the enhanced dendritic outgrowth. Cholesterol supplementation studies indicate that cholesterol reduction by CYP46A1 is the necessary trigger for these effects. These results were confirmed in vivo, with a significant increase of p-Trk, pre- and postsynaptic proteins, Rac1, and decreased cholesterol levels, in crude synaptosomal fractions prepared from CYP46A1 transgenic mouse cortex. This work describes the molecular mechanisms by which neuronal cholesterol metabolism effectively modulates neuronal outgrowth and synaptic markers.

Peroxisome Proliferator-activated Receptor γ Coactivator-1 α Isoforms Selectively Regulate Multiple Splicing Events on Target Genes

Endurance and resistance exercise training induces specific and profound changes in the skeletal muscle transcriptome. Peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α) coactivators are not only among the genes differentially induced by distinct training methods, but they also participate in the ensuing signaling cascades that allow skeletal muscle to adapt to each type of exercise. Although endurance training preferentially induces PGC-1α1 expression, resistance exercise activates the expression of PGC-1α2, -α3, and -α4. These three alternative PGC-1α isoforms lack the arginine/serine-rich (RS) and RNA recognition motifs characteristic of PGC-1α1. Discrete functions for PGC-1α1 and -α4 have been described, but the biological role of PGC-1α2 and -α3 remains elusive. Here we show that different PGC-1α variants can affect target gene splicing through diverse mechanisms, including alternative promoter usage. By analyzing the exon structure of the target transcripts for each PGC-1α isoform, we were able to identify a large number of previously unknown PGC-1α2 and -α3 target genes and pathways in skeletal muscle. In particular, PGC-1α2 seems to mediate a decrease in the levels of cholesterol synthesis genes. Our results suggest that the conservation of the N-terminal activation and repression domains (and not the RS/RNA recognition motif) is what determines the gene programs and splicing options modulated by each PGC-1α isoform. By using skeletal muscle-specific transgenic mice for PGC-1α1 and -α4, we could validate, in vivo, splicing events observed in in vitro studies. These results show that alternative PGC-1α variants can affect target gene expression both quantitatively and qualitatively and identify novel biological pathways under the control of this system of coactivators.

Bioenergetic cues shift FXR splicing towards FXRα2 to modulate hepatic lipolysis and fatty acid metabolism

Objective

Farnesoid X receptor (FXR) plays a prominent role in hepatic lipid metabolism. The FXR gene encodes four proteins with structural differences suggestive of discrete biological functions about which little is known.

Methods

We expressed each FXR variant in primary hepatocytes and evaluated global gene expression, lipid profile, and metabolic fluxes. Gene delivery of FXR variants to Fxr^−/− mouse liver was performed to evaluate their role in vivo. The effects of fasting and physical exercise on hepatic Fxr splicing were determined.

Results

We show that FXR splice isoforms regulate largely different gene sets and have specific effects on hepatic metabolism. FXRα2 (but not α1) activates a broad transcriptional program in hepatocytes conducive to lipolysis, fatty acid oxidation, and ketogenesis. Consequently, FXRα2 decreases cellular lipid accumulation and improves cellular insulin signaling to AKT. FXRα2 expression in Fxr^−/− mouse liver activates a similar gene program and robustly decreases hepatic triglyceride levels. On the other hand, FXRα1 reduces hepatic triglyceride content to a lesser extent and does so through regulation of lipogenic gene expression. Bioenergetic cues, such as fasting and exercise, dynamically regulate Fxr splicing in mouse liver to increase Fxrα2 expression.

Conclusions

Our results show that the main FXR variants in human liver (α1 and α2) reduce hepatic lipid accumulation through distinct mechanisms and to different degrees. Taking this novel mechanism into account could greatly improve the pharmacological targeting and therapeutic efficacy of FXR agonists.

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FXR variants regulate discrete gene programs with distinct biological outcomes.

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FXRα2 (but not α1) enhances fatty acid handling and insulin responsiveness.

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FXRα1 and α2 reduce liver lipid content through different mechanisms.

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Fasting and physical exercise dynamically regulate Fxr splicing in liver.

Intercellular: local and systemic actions of skeletal muscle PGC-1s

Physical exercise promotes complex adaptations in skeletal muscle that benefit various aspects of human health. Many of these adaptations are coordinated at the gene expression level by the concerted action of transcriptional regulators. Peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 (PGC-1) proteins play a prominent role in skeletal muscle transcriptional reprogramming induced by numerous stimuli. PGC-1s are master coactivators that orchestrate broad gene programs to modulate fuel supply and mitochondrial function, thus improving cellular energy metabolism. Recent studies unveiled novel biological functions for PGC-1s that extend well beyond skeletal muscle bioenergetics. Here we review recent advances in our understanding of PGC-1 actions in skeletal muscle, with special focus on their systemic effects.

[How to lose weight effectively and in a sustainable manner: a review of current topics]

There is a lot of conflicting information regarding the best way to lose weight, especially regarding food diets. A recent study compared the different diets and ultimately revealed that there is no significant difference in their efficacy for weight loss. Furthermore, it is recommended to lose weight gradually because rapid weight loss was a risk factor for more rapid and important weight regain. This notion has been challenged by a study that compared the two approaches and demonstrated that the rate of weight loss has no influence on weight regain. Ultimately, the key is to develop strategies that are best suited to the patient, so that he can adhere more easily and maintain his efforts on the long run.

[The cure of type 2 diabetes and patient education]

Type 2 diabetes is a potentially reversible disease. Patient education encompasses a deep investment of the health care providers, who with the aid of pedagogic tools, help the pa tient commit to this path. This facilitates the learning of uncommon knowledge and skills required. Whether or not it leads to a complete remission of the disease may not be the main purpose. The main goal lies in the patient's motivation to learn and change on a long term basis.

[Food addiction]

Food addiction is a common term used in everyday language by obese patients. Although the neurobiological evidence points to some similarities between addictive mechanisms and the consumption of certain foods, this diagnosis is not yet officially recognized. After a brief history of food addiction compared to other eating disorders, we review the neurobiological processes underlying this concept. A food addiction assessment tool is presented and discussed with the current literature and new classifications of the DSM-5. The concept of food addiction needs to be rethought and requires further research.

Edinburgh, the Scottish pioneers of anatomy and their lasting influence in South Africa

The history of the origin of anatomy education in South Africa is the history of an arduous journey through time. The lasting influence of Edinburgh came in the form of Robert Black Thomson. He was a student and assistant of Sir William Turner who gave rise to the first chair of anatomy and the establishment of a department at the South African College, known today as University of Cape Town. Thomson was later succeeded by Matthew Drennan, a keen anthropologist, who was revered by his students. This Scottish link prevailed over time with the appointment of Edward Philip Stibbe as the chair of anatomy at the South African School of Mines and Technology, which later became the University of the Witwatersrand. Stibbe’s successor, Raymond Arthur Dart, a graduate of the University of Sydney, was trained in an anatomy department sculpted on that of Edinburgh by Professor James Thomas Wilson. Wilson’s influence at the University of Sydney can be traced back to Edinburgh and William Turner through Thomas Anderson Stuart. Both Dart and Robert Broom, another Scot, were considered as Africa’s wild men by the late Professor Tobias. Here, the authors explore the Scottish link and origins of anatomy pedagogy in South Africa.