Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1

Myogenic differentiation is integral for the regeneration of skeletal muscle following tissue damage. Though high-energy post-mitotic muscle relies predominantly on mitochondrial respiration, the importance of mitochondrial remodeling in enabling muscle differentiation and the players involved are not fully known. Here we show that the mitochondrial fusion protein OPA1 is essential for muscle differentiation. Our study demonstrates that OPA1 loss or inhibition, through genetic and pharmacological means, abolishes in vivo muscle regeneration and in vitro myotube formation. We show that both the inhibition and genetic deletion of OPA1 prevent the early onset metabolic switch required to drive myoblast differentiation. In addition, we observe an OPA1-dependent upregulation of the supercomplex assembly factor, SCAF1, at the onset of differentiation. Importantly, preventing the upregulation of SCAF1, through OPA1 loss or siRNA-mediated SCAF1 knockdown, impairs metabolic reprogramming and muscle differentiation. These findings reveal the integral role of OPA1 and mitochondrial reprogramming at the onset of myogenic differentiation.

Evaluating mitochondrial length, volume, and cristae ultrastructure in rare mouse adult stem cell populations

Since changes in mitochondrial morphology regulate key functions of stem cells, it is important to assess their structure under physiological and pathophysiological conditions. Here, we present techniques optimized in rare adult muscle stem cells (MuSCs). For evaluating mitochondrial length and volume within a compact cytoplasmic area in MuSCs on intact myofibers, we describe steps for mitochondrial staining, imaging, and quantification. For evaluating mitochondrial ultrastructure in small cell numbers, we describe steps for agarose embedding and quantification by TEM. For complete details on generation and use of this protocol, please refer to Baker et al. (2022).1.

Relationship between Mitochondrial Quality Control Markers, Lower Extremity Tissue Composition, and Physical Performance in Physically Inactive Older Adults

Altered mitochondrial quality and function in muscle may be involved in age-related physical function decline. The role played by the autophagy-lysosome system, a major component of mitochondrial quality control (MQC), is incompletely understood. This study was undertaken to obtain initial indications on the relationship between autophagy, mitophagy, and lysosomal markers in muscle and measures of physical performance and lower extremity tissue composition in young and older adults. Twenty-three participants were enrolled, nine young (mean age: 24.3 ± 4.3 years) and 14 older adults (mean age: 77.9 ± 6.3 years). Lower extremity tissue composition was quantified volumetrically by magnetic resonance imaging and a tissue composition index was calculated as the ratio between muscle and intermuscular adipose tissue volume. Physical performance in older participants was assessed via the Short Physical Performance Battery (SPPB). Protein levels of the autophagy marker p62, the mitophagy mediator BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), the lysosomal markers transcription factor EB, vacuolar-type ATPase, and lysosomal-associated membrane protein 1 were measured by Western immunoblotting in vastus lateralis muscle biopsies. Older adults had smaller muscle volume and lower tissue composition index than young participants. The protein content of p62 and BNIP3 was higher in older adults. A negative correlation was detected between p62 and BNIP3 and the tissue composition index. p62 and BNIP3 were also related to the performance on the 5-time sit-to-stand test of the SPPB. Our results suggest that an altered expression of markers of the autophagy/mitophagy-lysosomal system is related to deterioration of lower extremity tissue composition and muscle dysfunction. Additional studies are needed to clarify the role of defective MQC in human muscle aging and identify novel biological targets for drug development.

Scientific meeting report: International Biochemistry of Exercise 2022

Exercise is one of the only nonpharmacological remedies known to counteract genetic and chronic diseases by enhancing health and improving life span. Although the many benefits of regular physical activity have been recognized for some time, the intricate and complex signaling systems triggered at the onset of exercise have only recently begun to be uncovered. Exercising muscles initiate a coordinated, multisystemic, metabolic rewiring, which is communicated to distant organs by various molecular mediators. The field of exercise research has been expanding beyond the musculoskeletal system, with interest from industry to provide realistic models and exercise mimetics that evoke a whole body rejuvenation response. The 18th International Biochemistry of Exercise conference took place in Toronto, Canada, from May 25 to May 28, 2022, with more than 400 attendees. Here, we provide an overview of the most cutting-edge exercise-related research presented by 66 speakers, focusing on new developments in topics ranging from molecular and cellular mechanisms of exercise adaptations to exercise therapy and management of disease and aging. We also describe how the manipulation of these signaling pathways can uncover therapeutic avenues for improving human health and quality of life.

Denervation induces mitochondrial decline and exacerbates lysosome dysfunction in middle-aged mice

With age, skeletal muscle undergoes a progressive decline in size and quality. Imbalanced mitochondrial turnover and the resultant dysfunction contribute to these phenotypic alterations. Motor neuron denervation (Den) is a contributor to the etiology of muscle atrophy associated with age. Further, aged muscle exhibits reduced plasticity to both enhanced and suppressed contractile activity. It remains unclear when the onset of this blunted response occurs, and how middle-aged muscle adapts to denervation. The purpose of this study was to compare mitochondrial turnover pathways in young (Y, ~5months) and middle-aged (MA, ~15months) mice, and determine the influence of Den. Transgenic mt-Keima mice were subjected to 1,3 or 7 days of Den. Muscle mass, mitochondrial content, and PGC-1α protein were not different between Y and MA mice. However, indications of enhanced mitochondrial fission and mitophagy were evident in MA muscle which were supported by a greater abundance of lysosome proteins. Den resulted in muscle atrophy and reductions in mitochondrial protein content by 7-days. These changes occurred concomitant with modest decreases in PGC-1α protein, but without further elevations in mitophagy. Although both autophagosomal and lysosomal proteins were elevated, evidence of lysosome dysfunction was present following Den in MA mice. These data suggest that increases in fission drive an acceleration of mitophagy in muscle of MA mice to preserve mitochondrial quality. Den exacerbates the aging phenotype by reducing biogenesis in the absence of a change in mitophagy, perhaps limited by lysosomal capacity, leading to an accumulation of dysfunctional mitochondria with an age-related loss of neuromuscular innervation.

The influence of age, sex, and exercise on autophagy, mitophagy, and lysosome biogenesis in skeletal muscle

Background

Aging decreases skeletal muscle mass and quality. Maintenance of healthy muscle is regulated by a balance between protein and organellar synthesis and their degradation. The autophagy-lysosome system is responsible for the selective degradation of protein aggregates and organelles, such as mitochondria (i.e., mitophagy). Little data exist on the independent and combined influence of age, biological sex, and exercise on the autophagy system and lysosome biogenesis. The purpose of this study was to characterize sex differences in autophagy and lysosome biogenesis in young and aged muscle and to determine if acute exercise influences these processes.

Methods

Young (4–6 months) and aged (22–24 months) male and female mice were assigned to a sedentary or an acute exercise group. Mitochondrial content, the autophagy-lysosome system, and mitophagy were measured via protein analysis. A TFEB-promoter-construct was utilized to examine Tfeb transcription, and nuclear-cytosolic fractions allowed us to examine TFEB localization in sedentary and exercised muscle with age and sex.

Results

Our results indicate that female mice, both young and old, had more mitochondrial protein than age-matched males. However, mitochondria in the muscle of females had a reduced respiratory capacity. Mitochondrial content was only reduced with age in the male cohort. Young female mice had a greater abundance of autophagy, mitophagy, and lysosome proteins than young males; however, increases were evident with age irrespective of sex. Young sedentary female mice had indices of greater autophagosomal turnover than male counterparts. Exhaustive exercise was able to stimulate autophagic clearance solely in young male mice. Similarly, nuclear TFEB protein was enhanced to a greater extent in young male, compared to young female mice following exercise, but no changes were observed in aged mice. Finally, TFEB-promoter activity was upregulated following exercise in both young and aged muscle.

Conclusions

The present study demonstrates that biological sex influences mitochondrial homeostasis, the autophagy-lysosome system, and mitophagy in skeletal muscle with age. Furthermore, our data suggest that young male mice have a more profound ability to activate these processes with exercise than in the other groups. Ultimately, this may contribute to a greater remodeling of muscle in response to exercise training in males.

Manifestations of Age on Autophagy, Mitophagy and Lysosomes in Skeletal Muscle

Sarcopenia is the loss of both muscle mass and function with age. Although the molecular underpinnings of sarcopenia are not fully understood, numerous pathways are implicated, including autophagy, in which defective cargo is selectively identified and degraded at the lysosome. The specific tagging and degradation of mitochondria is termed mitophagy, a process important for the maintenance of an organelle pool that functions efficiently in energy production and with relatively low reactive oxygen species production. Emerging data, yet insufficient, have implicated various steps in this pathway as potential contributors to the aging muscle atrophy phenotype. Included in this is the lysosome, the end-stage organelle possessing a host of proteolytic and degradative enzymes, and a function devoted to the hydrolysis and breakdown of defective molecular complexes and organelles. This review provides a summary of our current understanding of how the autophagy-lysosome system is regulated in aging muscle, highlighting specific areas where knowledge gaps exist. Characterization of the autophagy pathway with a particular focus on the lysosome will undoubtedly pave the way for the development of novel therapeutic strategies to combat age-related muscle loss.

Mitochondrial breakdown in skeletal muscle and the emerging role of the lysosomes

Skeletal muscle mitochondria are essential in providing the energy required for locomotion. In response to contractile activity, the production of mitochondria is upregulated to meet the energy demands placed upon muscle cells. In a coordinated fashion, exercise also promotes the breakdown of dysfunctional mitochondria via mitophagy. Mitophagy is characterized by the selection of poorly functioning organelles, engulfment in an autophagosome and transport to lysosomes for degradation. In addition to the activation of mitophagy, exercise also elevates lysosome biogenesis. This coordinated increase in mitophagy targeting and lysosomal biogenesis serves to enhance the capacity for autophagosomal degradation, thereby aiding in the maintenance of mitochondrial quality. Lysosome dysfunction, as observed in lysosomal storage disorders (LSDs), negatively impacts mitochondrial function likely through the suppression of mitophagy. Since exercise is capable of activating mitophagy and lysosome biogenesis, researchers have begun to investigate physical activity as an effective therapy for LSDs. This review summarizes the current understanding of how mitophagy and lysosomal biogenesis are regulated in exercising skeletal, with potential therapeutic implications.

The Role of p53 in Determining Mitochondrial Adaptations to Endurance Training in Skeletal Muscle

p53 plays an important role in regulating mitochondrial homeostasis. However, it is unknown whether p53 is required for the physiological and mitochondrial adaptations with exercise training. Furthermore, it is also unknown whether impairments in the absence of p53 are a result of its loss in skeletal muscle, or a secondary effect due to its deletion in alternative tissues. Thus, we investigated the role of p53 in regulating mitochondria both basally, and under the influence of exercise, by subjecting C57Bl/6J whole-body (WB) and muscle-specific p53 knockout (mKO) mice to a 6-week training program. Our results confirm that p53 is important for regulating mitochondrial content and function, as well as proteins within the autophagy and apoptosis pathways. Despite an increased proportion of phosphorylated p53 (Ser¹⁵) in the mitochondria, p53 is not required for training-induced adaptations in exercise capacity or mitochondrial content and function. In comparing mouse models, similar directional alterations were observed in basal and exercise-induced signaling modifications in WB and mKO mice, however the magnitude of change was less pronounced in the mKO mice. Our data suggest that p53 is required for basal mitochondrial maintenance in skeletal muscle, but is not required for the adaptive responses to exercise training.

Maintenance of Skeletal Muscle Mitochondria in Health, Exercise, and Aging

Mitochondria are critical organelles responsible for regulating the metabolic status of skeletal muscle. These organelles exhibit remarkable plasticity by adapting their volume, structure, and function in response to chronic exercise, disuse, aging, and disease. A single bout of exercise initiates signaling to provoke increases in mitochondrial biogenesis, balanced by the onset of organelle turnover carried out by the mitophagy pathway. This accelerated turnover ensures the presence of a high functioning network of mitochondria designed for optimal ATP supply, with the consequence of favoring lipid metabolism, maintaining muscle mass, and reducing apoptotic susceptibility over the longer term. Conversely, aging and disuse are associated with reductions in muscle mass that are in part attributable to dysregulation of the mitochondrial network and impaired mitochondrial function. Therefore, exercise represents a viable, nonpharmaceutical therapy with the potential to reverse and enhance the impaired mitochondrial function observed with aging and chronic muscle disuse.

Considerations for Water Disposal and Management in the Development of Coalbed Methane Resources in Rural Alaska

Abstract

The objective of this study is to evaluate the alternatives for water disposal and management during coalbed methane production in remote arctic conditions. In this paper, we evaluate five methods of water disposal in the arctic environment. These methods are (1) direct discharge onto the surface, (2) controlled discharge into streams, (3) underground injection using wells, (4) concentration of produced saline water in a multiple effect evaporator, and (5) conversion of wastewater into clean water by reverse osmosis, a submerged combustion evaporator, and a pulse combustion dryer. The methods were ranked based on a set of criteria including logistics and engineering challenges of water treatment and processing in the arctic, environmental regulations, costs of installation, operations and maintenance. We conclude that surface discharge by use of ground sprinklers is not acceptable in the arctic; use of injection wells and the freeze thaw/evaporation processes hold promise for dewatering coalbed methane wells in rural Alaska.

Introduction

Coalbed methane has become an important source of natural gas production in the Lower 48 States and other places around the world. One current estimate shows that coal basins in the State of Alaska contain over 28 to 43 trillion standard cubic metres (1,000 to 1,500 trillion standard cubic feet) of coalbed methane. Although the actual extent and magnitude of producible gas from Alaska's remote coal basins are unknown, the Alaska Department of Natural Resources postulates that if only 10% on the estimated 28 trillion cubic metres of methane gas is recoverable, this coalbed methane resource would triple the State's current proven conventional gas reserves(1). Exploratory drilling is the key to delineating the potential of the coalbed gas resources of Alaska.

Coalbeds are naturally fractured, low pressure, water saturated gas reservoirs. In a coalbed methane reservoir, even though some free gas may exist in the coal deposits, the majority of the gas is adsorbed on the surface of the coal matrix. Proper dewatering of the coal seams is a critical factor associated with gas production from coalbed methane reservoirs. The saline water that is trapped within the deeply buried coal seams must be removed in order to reduce the pressure of the system, and allow the gas to desorbs from the coals and flow into the wellbore. Large amounts of water production can be anticipated during exploration drilling and early life of the producing field.

There are three different mechanisms by which water can be stored in coal seams. First, adherent moisture or bulk moisture refers to the free water contained in the cleat system that has a normal vapor pressure(2,3). This is the volume of water that must be removed during the dewatering phase in the coalbed methane production operations. Second, inherent moisture or absorbed moisture is the water in the microspore system that decreases the adsorptive capacity of the coal for methane(3). Although this type of water storage is inconsequential when considering water disposal, it is extremely detrimental to the gas concentration of the coal. The other forms of water found in coal seams include chemically bound water and water of hydration.