The Role of Mitochondrial Stress in Muscle Wasting Following Severe Burn Trauma

Farnesysltransferase Inhibitor Prevents Burn Injury-Induced Metabolome Changes in Muscle

Burn injury remains a significant public health issue worldwide. Metabolic derangements are a major complication of burn injury and negatively affect the clinical outcomes of severely burned patients. These metabolic aberrations include muscle wasting, hypermetabolism, hyperglycemia, hyperlactatemia, insulin resistance, and mitochondrial dysfunction. However, little is known about the impact of burn injury on the metabolome profile in skeletal muscle. We have previously shown that farnesyltransferase inhibitor (FTI) reverses burn injury-induced insulin resistance, mitochondrial dysfunction, and the Warburg effect in mouse skeletal muscle. To evaluate metabolome composition, targeted quantitative analysis was performed using capillary electrophoresis mass spectrometry in mouse skeletal muscle. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and hierarchical cluster analysis demonstrated that burn injury induced a global change in metabolome composition. FTI treatment almost completely prevented burn injury-induced alterations in metabolite levels. Pathway analysis revealed that the pathways most affected by burn injury were purine, glutathione, β-alanine, glycine, serine, and threonine metabolism. Burn injury induced a suppressed oxidized to reduced nicotinamide adenine dinucleotide (NAD⁺/NADH) ratio as well as oxidative stress and adenosine triphosphate (ATP) depletion, all of which were reversed by FTI. Moreover, our data raise the possibility that burn injury may lead to increased glutaminolysis and reductive carboxylation in mouse skeletal muscle.

Edward F. Adolph Distinguished Lecture. It's more than skin deep: thermoregulatory and cardiovascular consequences of severe burn injuries in humans

Each year, within the United States, tens of thousands of individuals are hospitalized for burn-related injuries. The treatment of deep burns often involves skin grafts to accelerate healing and reduce the risk of infection. The grafting procedure results in a physical disruption between the injured and subsequently debrided host site and the skin graft placed on top of that site. Both neural and vascular connections must occur between the host site and the graft for neural modulation of skin blood flow to take place. Furthermore, evaporative cooling from such burn injured areas is effectively absent, leading to greatly impaired thermoregulatory responses in individuals with large portions of their body surface area burned. Hospitalization following a burn injury can last weeks to months, with cardiovascular and metabolic consequences of such injuries having the potential to adversely affect the burn survivor for years postdischarge. With that background, the objectives of this article are to discuss 1) our current understanding of the physiology and associated consequences of skin grafting, 2) the effects of skin grafts on efferent thermoregulatory responses and the associated consequences pertaining to whole body thermoregulation, 3) approaches that may reduce the risk of excessive hyperthermia in burn survivors, 4) the long-term cardiovascular consequences of burn injuries, and 5) the extent to which burn survivors can "normalize" otherwise compromised cardiovascular responses. Our primary objective is to guide the reader toward an understanding that severe burn injuries result in significant physiological consequences that can persist for years after the injury.

The connection between the dynamic remodeling of the mitochondrial network and the regulation of muscle mass

The dynamic coordination of processes controlling the quality of the mitochondrial network is crucial to maintain the function of mitochondria in skeletal muscle. Changes of mitochondrial proteolytic system, dynamics (fusion/fission), and mitophagy induce pathways that affect muscle mass and performance. When muscle mass is lost, the risk of disease onset and premature death is dramatically increased. For instance, poor quality of muscles correlates with the onset progression of several age-related disorders such as diabetes, obesity, cancer, and aging sarcopenia. To date, there are no drug therapies to reverse muscle loss, and exercise remains the best approach to improve mitochondrial health and to slow atrophy in several diseases. This review will describe the principal mechanisms that control mitochondrial quality and the pathways that link mitochondrial dysfunction to muscle mass regulation.

Erythropoietin Alleviates Burn-induced Muscle Wasting

Background: Burn injury induces long-term skeletal muscle pathology. We hypothesized EPO could attenuate burn-induced muscle fiber atrophy. Methods: Rats were allocated into four groups: a sham burn group, an untreated burn group subjected to third degree hind paw burn, and two burn groups treated with weekly or daily EPO for four weeks. Gastrocnemius muscle was analyzed at four weeks post-burn. Results: EPO attenuated the reduction of mean myofiber cross-sectional area post-burn and the level of the protective effect was no significant difference between two EPO-treated groups (p=0.784). Furthermore, EPO decreased the expression of atrophy-related ubiquitin ligase, atrogin-1, which was up-regulated in response to burn. Compared to untreated burn rats, those receiving weekly or daily EPO groups had less cell apoptosis by TUNEL assay. EPO decreased the expression of cleaved caspase 3 (key factor in the caspase-dependent pathway) and apoptosis-inducing factor (implicated in the caspase-independent pathway) after burn. Furthermore, EPO alleviated connective tissue overproduction following burn via transforming growth factor beta 1-Smad2/3 pathway. Daily EPO group caused significant erythrocytosis compared with untreated burn group but not weekly EPO group. Conclusion: EPO therapy attenuated skeletal muscle apoptosis and fibrosis at four weeks post-burn. Weekly EPO may be a safe and effective option in muscle wasting post-burn.

Oxidative pathophysiology following volumetric muscle loss injury in a porcine model

Volumetric muscle loss (VML) occurs after severe orthopedic trauma and results in loss of muscle fibers and function that can leave patients permanently disabled. Although animals models of VML are useful to test possible therapeutic strategies, the pathophysiological characteristics of remaining skeletal muscle and changes in metabolism are not thoroughly understood. Herein, alterations of neuromuscular function, muscle fiber morphology, myosin heavy chain expression, and myofiber mitochondrial respiration were evaluated in an adult Yorkshire swine VML injury model. VML injured animals showed reduced peak isometric strength (P < 0.05) and a shift toward smaller muscle fibers independent of fiber type (P < 0.001). The muscle remaining after VML had a greater distribution of type I fibers and lower distribution of type II fibers (P < 0.001). Skeletal muscle mitochondrial state 2 and state 3, reflecting complex I respiration, increased after injury (P < 0.05) with a consistent trend to display higher oxygen flux per milligram of tissue. However, this was largely driven by increased mitochondrial content after VML which was associated with higher mitochondrial fission (FIS-1 protein levels). This study demonstrates an underlying perturbation of oxidative metabolism within the remaining musculature following surgical creation of an isolated, sterile VML injury in a porcine model that may be influential to the development of insidious pathophysiology and regenerative and rehabilitative therapies. NEW & NOTEWORTHY The natural injury sequela of volumetric muscle loss (VML) and associated pathophysiology of the remaining muscle is still incompletely understood. Herein we demonstrate a chronic muscle function deficit, with an increase in type I muscle fibers and parallel increase in oxidative capacity of remaining skeletal muscle. It is possible that the alteration in oxidative capacity after VML could largely be due to heightened mitochondrial activity and an increase in mitochondrial abundance.