The dominance of dorsal scapular artery as the blood supply to muscles of the back in the absence of two primary vessels: a cadaveric case report.

PURPOSE: Understanding of rare or unknown anatomical variations of the vasculature of the neck is critical to reduce the risk of complications during surgeries and other invasive procedures in the neck and shoulder regions. METHODS: Bilateral dissection of the neck and muscles of the back of an 87-year-old Caucasian male donor was performed to demonstrate the origin, course and termination of the arteries that arise in the neck. RESULTS: Several anatomical variations were noted on the right side of the neck of the donor body - (i) only inferior thyroid and ascending cervical arteries originated from the thyrocervical trunk (TCT), from the first part of the subclavian artery (SA), whereas the transverse cervical (TCA) and suprascapular (SSA) arteries were entirely absent, (ii) Dorsal scapular artery (DSA) emerged normally from the third part of the SA. However, after supplying the rhomboids and levator scapulae muscles, DSA provided two additional branches to the trapezius muscle and a branch to the supraspinatus muscle. Interestingly, the branches to the trapezius muscle from the DSA were the only sources of blood supply to the muscle. CONCLUSION: We report a unique anatomical variation involving the absence of the TCA and SSA from the TCT. The unilateral absence of these major vessels and the branches of DSA supplying the trapezius and supraspinatus muscles have not been reported previously in the literature in a single case report. This case study may provide useful information for head and neck reconstruction and shoulder repair surgeries.

Triple variation in the vascular supply in the neck of a female donor body: a case report.

PURPOSE: Understanding the anatomical variations involving bifurcation of the common carotid artery, positioning of external and internal carotid arteries, and branching of the external carotid artery are of vital importance in neck surgeries such as carotid endarterectomies (CEA). METHODS: The neck of a 51-year-old female donor body was dissected to demonstrate the arterial network. RESULTS: Bifurcation of the common carotid artery occurred at the level of the C6-C7 intervertebral disc, significantly inferior to the generally accepted and taught anatomical location at the level of intervertebral disc between C3 and C4 vertebrae. When the arteries were followed superiorly after the bifurcation, a unique second variation was observed: translocation of the external and internal carotid arteries. The external carotid artery was located posterolaterally and the internal carotid artery was located more medially. Finally, a third variation was discovered in the form of a common thyrolingual trunk that gave rise to superior thyroid and lingual arteries rather than these arising independently from the external carotid artery. CONCLUSIONS: We report a unique triple variation within the major arteries of the neck that has not been previously reported in surveyed literature. This case report may provide useful information for cardiovascular surgeons performing CEA and for otolaryngologists performing prophylactic arterial ligation following transoral robotic surgery for oropharyngeal cancer resection.

Role of Three-Dimensional Visualization Modalities in Medical Education.

For the past two decades, slide-based presentation has been the method of content delivery in medical education. In recent years, other teaching modalities involving three-dimensional (3D) visualization such as 3D printed anatomical models, virtual reality (VR), and augmented reality (AR) have been explored to augment the education experience. This review article will analyze the use of slide-based presentation, 3D printed anatomical models, AR, and VR technologies in medical education, including their benefits and limitations.

Superoxide-mediated oxidative stress accelerates skeletal muscle atrophy by synchronous activation of proteolytic systems.

The maintenance of skeletal muscle mass depends on the overall balance between the rates of protein synthesis and degradation. Thus, age-related muscle atrophy and function, commonly known as sarcopenia, may result from decreased protein synthesis, increased proteolysis, or simultaneous changes in both processes governed by complex multifactorial mechanisms. Growing evidence implicates oxidative stress and reactive oxygen species (ROS) as an essential regulator of proteolysis. Our previous studies have shown that genetic deletion of CuZn superoxide dismutase (CuZnSOD, Sod1) in mice leads to elevated oxidative stress, muscle atrophy and weakness, and an acceleration in age-related phenotypes associated with sarcopenia. The goal of this study is to determine whether oxidative stress directly influences the acceleration of proteolysis in skeletal muscle of Sod1-/- mice as a function of age. Compared to control, Sod1-/- muscle showed a significant elevation in protein carbonyls and 3-nitrotyrosine levels, suggesting high oxidative and nitrosative protein modifications were present. In addition, age-dependent muscle atrophy in Sod1-/- muscle was accompanied by an upregulation of the cysteine proteases, calpain, and caspase-3, which are known to play a key role in the initial breakdown of sarcomeres during atrophic conditions. Furthermore, an increase in oxidative stress-induced muscle atrophy was also strongly coupled with simultaneous activation of two major proteolytic systems, the ubiquitin-proteasome and lysosomal autophagy pathways. Collectively, our data suggest that chronic oxidative stress in Sod1-/- mice accelerates age-dependent muscle atrophy by enhancing coordinated activation of the proteolytic systems, thereby resulting in overall protein degradation.

A Three-Dimensional Print Model of the Pterygopalatine Fossa Significantly Enhances the Learning Experience.

The pterygopalatine fossa (PPF) is a bilateral space deep within the skull that serves as a major neurovascular junction. However, its small volume and poor accessibility make it a difficult space to comprehend using two-dimensional illustrations and cadaveric dissections. A three-dimensional (3D) printed model of the PPF was developed as a visual and kinesthetic learning tool for completely visualizing the fossa, its boundaries, its communicating channels, and its neurovascular structures. The model was evaluated by analyzing student performance on pre- and post-quizzes and a student satisfaction survey based on the five-point Likert scale. The first cohort comprised of 88 students who had never before studied the PPF. The second cohort consisted of 30 students who were previously taught the PPF. Each cohort was randomly divided into a control group who were provided with a half skull and an intervention group that were provided with the 3D printed model. The intervention group performed significantly better on the post-quiz as compared to the control group in cohort I (P = 0.001); while not significant, it also improved learning in cohort II students (P = 0.124). Satisfaction surveys indicated that the intervention group found the 3D printed model to be significantly more useful (P < 0.05) as compared to the half skull used by the control group. Importantly, the effect sizes for cohorts I and II (0.504 and 0.581, respectively) validated the statistical results. Together, this study highlights the importance of 3D printed models as teaching tools in anatomy education.

Mitochondrial-targeted methionine sulfoxide reductase overexpression increases the production of oxidative stress in mitochondria from skeletal muscle.

OBJECTIVE: Mitochondrial dysfunction comprises part of the etiology of myriad health issues, particularly those that occur with advancing age. Methionine sulfoxide reductase A (MsrA) is a ubiquitous protein oxidation repair enzyme that specifically and catalytically reduces a specific epimer of oxidized methionine: methionine sulfoxide. In this study, we tested the ways in which mitochondrial bioenergetic functions are affected by increasing MsrA expression in different cellular compartments. METHODS: In this study, we tested the function of isolated mitochondria, including free radical generation, ATP production, and respiration, from the skeletal muscle of two lines of transgenic mice with increased MsrA expression: mitochondria-targeted MsrA overexpression or cytosol-targeted MsrA overexpression. RESULTS: Surprisingly, in the samples from mice with mitochondrial-targeted MsrA overexpression, we found dramatically increased free radical production though no specific defect in respiration, ATP production, or membrane potential. Among the electron transport chain complexes, we found the activity of complex I was specifically reduced in mitochondrial MsrA transgenic mice. In mice with cytosolic-targeted MsrA overexpression, we found no significant alteration made to any of these parameters of mitochondrial energetics. CONCLUSIONS: There is also a growing amount of evidence that MsrA is a functional requirement for sustaining optimal mitochondrial respiration and free radical generation. MsrA is also known to play a partial role in maintaining normal protein homeostasis by specifically repairing oxidized proteins. Our studies highlight a potential novel role for MsrA in regulating the activity of mitochondrial function through its interaction with the mitochondrial proteome.

Case report of unique anastomosis between facial and inferior alveolar arteries.

PURPOSE: Understanding anatomical variations of the facial artery and its branches is important for dental and medical practitioners. METHODS: Routine cadaveric dissection of the head and neck was performed to demonstrate the origin and branches of the facial artery. RESULTS: Facial artery emerged from a common linguofacial trunk off the external carotid artery. On the face, the facial artery first gave off a pre-masseteric branch. Immediately after, an aberrant artery emerged from the facial artery that coursed along the ramus of the mandible, which upon further dissection and examination was found to anastomose with inferior alveolar artery within the ramus of the mandible. CONCLUSIONS: We report a unique anastomosis between facial and inferior alveolar arteries, vessels that have not been previously shown to communicate. This case report may provide useful information for oral and maxillofacial surgeons as well as dentists performing inferior alveolar nerve blocks.

Sustained NFκB inhibition improves insulin sensitivity but is detrimental to muscle health.

Older adults universally suffer from sarcopenia and approximately 60-70% are diabetic or prediabetic. Nonetheless, the mechanisms underlying these aging-related metabolic disorders are unknown. NFκB has been implicated in the pathogenesis of several aging-related pathologies including sarcopenia and type 2 diabetes and has been proposed as a target against them. NFκB also is thought to mediate muscle wasting seen with disuse, denervation, and some systemic diseases (e.g., cancer, sepsis). We tested the hypothesis that lifelong inhibition of the classical NFκB pathway would protect against aging-related sarcopenia and insulin resistance. Aged mice with muscle-specific overexpression of a super-repressor IκBα mutant (MISR) were protected from insulin resistance. However, MISR mice were not protected from sarcopenia; to the contrary, these mice had decreases in muscle mass and strength compared to wild-type mice. In MISR mice, NFκB suppression also led to an increase in proteasome activity and alterations in several genes and pathways involved in muscle growth and atrophy (e.g., myostatin). We conclude that the mechanism behind aging-induced sarcopenia is NFκB independent and differs from muscle wasting due to pathologic conditions. Our findings also indicate that, while suppressing NFκB improves insulin sensitivity in aged mice, this transcription factor is important for normal muscle mass maintenance and its sustained inhibition is detrimental to muscle function.

Oxidative damage to myelin proteins accompanies peripheral nerve motor dysfunction in aging C57BL/6 male mice.

Aging is associated with a decline in peripheral nerve function of both motor and sensory nerves. The decline in function of peripheral sensorimotor nerves with aging has been linked to sarcopenia, the age-related decline in muscle mass and function that significantly compromises the quality of life in older humans. In this study, we report a significant increase in oxidized fatty acids and insoluble protein carbonyls in sciatic nerves of aged C57BL/6 male mice (28-30mo) that exhibit a profound decline in motor nerve function and degenerative changes in both axon and myelin structure, compared to young mice (6-8mo). Our data further suggests that this age-related loss of function of peripheral motor nerves is likely precipitated by changes in mechanisms that protect and/or repair oxidative damage. We predict that interventions that target these mechanisms may protect against age-related decline in peripheral sensorimotor nerve function and likely improve the debilitating outcome of sarcopenia in older humans.

Moderate modulation of disease in the G93A model of ALS by the compound 2-(2-hydroxyphenyl)-benzoxazole (HBX).

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurological disease characterized by degeneration and death of motor neurons. Aberrant protein aggregation and oxidative stress are implicated in the etiology of ALS; thus preventing propagation of early aggregation events and oxidative damage could be an effective therapy. We tested the effect of dietary supplementation (initiated 40 days of age) with 2-(2-hydroxyphenyl)-benzoxazole (HBX), a compound with metal chelator and anti-aggregation properties, on disease onset, progression and lifespan in the G93A mouse model of ALS. Tests were not sufficiently powerful to detect any change to survival distribution of mice treated with HBX. However, the disease onset was delayed and max lifespan was increased in the treatment group. Additionally, disease progression was moderated as shown by reduced neuromuscular denervation measured by repetitive nerve stimulation. F2-isoprostanes, a marker of oxidative damage, are elevated in skeletal muscle from G93A mice at onset and this increase is prevented in HBX fed G93A mice. Furthermore, HBX treatment reduced mutant SOD1 protein aggregation in whole spinal cord of G93A mice at disease onset. Overall, our data suggests that HBX may be able to improve the degenerative symptoms of ALS through the prevention of oxidative damage and protein aggregation. Further studies are needed to uncover the mechanistic effects of HBX in ameliorating ALS pathology.

Fluorescence-Based Approaches for Quantitative Assessment of Protein Carbonylation, Protein Disulfides, and Protein Conformation in Biological Tissues.

Protein oxidation and misfolding have been considered as key players for progression of aging and etiology of various pathological conditions. However, few attempts have been made to develop sensitive and reproducible assays to quantify the changes in protein oxidation and alteration in structure. Here we describe three distinct fluorescence-based assays to quantify changes in protein oxidation, namely carbonylation and disulfides and alteration in protein surface hydrophobicity as a reporter for protein conformation. These techniques will provide investigators the opportunity to address important biological questions in their experimental models.

The histone deacetylase inhibitor butyrate improves metabolism and reduces muscle atrophy during aging.

Sarcopenia, the loss of skeletal muscle mass and function during aging, is a major contributor to disability and frailty in the elderly. Previous studies found a protective effect of reduced histone deacetylase activity in models of neurogenic muscle atrophy. Because loss of muscle mass during aging is associated with loss of motor neuron innervation, we investigated the potential for the histone deacetylase (HDAC) inhibitor butyrate to modulate age-related muscle loss. Consistent with previous studies, we found significant loss of hindlimb muscle mass in 26-month-old C57Bl/6 female mice fed a control diet. Butyrate treatment starting at 16 months of age wholly or partially protected against muscle atrophy in hindlimb muscles. Butyrate increased muscle fiber cross-sectional area and prevented intramuscular fat accumulation in the old mice. In addition to the protective effect on muscle mass, butyrate reduced fat mass and improved glucose metabolism in 26-month-old mice as determined by a glucose tolerance test. Furthermore, butyrate increased markers of mitochondrial biogenesis in skeletal muscle and whole-body oxygen consumption without affecting activity. The increase in mass in butyrate-treated mice was not due to reduced ubiquitin-mediated proteasomal degradation. However, butyrate reduced markers of oxidative stress and apoptosis and altered antioxidant enzyme activity. Our data is the first to show a beneficial effect of butyrate on muscle mass during aging and suggests HDACs contribute to age-related muscle atrophy and may be effective targets for intervention in sarcopenia and age-related metabolic disease.

Butyrate prevents muscle atrophy after sciatic nerve crush.

INTRODUCTION: Histone deacetylases (HDACs) have been implicated in neurogenic muscle atrophy, but the mechanisms by which HDAC inhibitors might have beneficial effects are not defined. METHODS: We used sciatic nerve crush to determine the effect of butyrate on denervation-induced gene expression and oxidative stress. RESULTS: Butyrate treatment initiated 3 weeks before injury and continued 1 week after injury increases histone acetylation and reduces muscle atrophy after nerve crush. Butyrate delivered only after nerve crush similarly prevented muscle atrophy. Butyrate had no effect on the increase in histone deacetylase 4 (HDAC4) protein levels following nerve crush but prevented the increase in expression of myogenin, MuRF1, and atrogin-1. Butyrate did not affect mitochondrial reactive oxygen species production, but it increased antioxidant enzyme activity, reduced proteasome activity, and reduced oxidative damage following nerve injury. CONCLUSIONS: These data suggest that HDAC inhibitors are promising pharmacological agents for treating neurogenic muscle atrophy. Muscle Nerve 52: 859-868, 2015.

Complex IV-deficient Surf1(-/-) mice initiate mitochondrial stress responses.

Mutations in SURF1 (surfeit locus protein 1) COX (cytochrome c oxidase) assembly protein are associated with Leigh's syndrome, a human mitochondrial disorder that manifests as severe mitochondrial phenotypes and early lethality. In contrast, mice lacking the SURF1 protein (Surf1-/-) are viable and were previously shown to have enhanced longevity and a greater than 50% reduction in COX activity. We measured mitochondrial function in heart and skeletal muscle, and despite the significant reduction in COX activity, we found little or no difference in ROS (reactive oxygen species) generation, membrane potential, ATP production or respiration in isolated mitochondria from Surf1-/- mice compared with wild-type. However, blood lactate levels were elevated and Surf1-/- mice had reduced running endurance, suggesting compromised mitochondrial energy metabolism in vivo. Decreased COX activity in Surf1-/- mice is associated with increased markers of mitochondrial biogenesis [PGC-1α (peroxisome-proliferator-activated receptor γ co-activator 1α) and VDAC (voltage-dependent anion channel)] in both heart and skeletal muscle. Although mitochondrial biogenesis is a common response in the two tissues, skeletal muscle has an up-regulation of the UPRMT (mitochondrial unfolded protein response) and heart exhibits induction of the Nrf2 (nuclear factor-erythroid 2-related factor 2) antioxidant response pathway. These data are the first to show induction of the UPRMT in a mammalian model of decreased COX activity. In addition, the results of the present study suggest that impaired mitochondrial function can lead to induction of mitochondrial stress pathways to confer protective effects on cellular homoeostasis.

Neuronal cells but not muscle cells are resistant to oxidative stress mediated protein misfolding and cell death: role of molecular chaperones.

Our recent study in a mouse model of familial-Amyotrophic Lateral Sclerosis (f-ALS) revealed that muscle proteins are equally sensitive to misfolding as spinal cord proteins despite the presence of low mutant CuZn-superoxide dismutase, which is considered to be the key toxic element for initiation and progression of f-ALS. More importantly, we observed differential level of heat shock proteins (Hsp's) between skeletal muscle and spinal cord tissues prior to the onset and during disease progression; spinal cord maintains significantly higher level of Hsp's compared to skeletal muscle. In this study, we report two important observations; (i) muscle cells (but not neuronal cells) are extremely vulnerable to protein misfolding and cell death during challenge with oxidative stress and (ii) muscle cells fail to mount Hsp's during challenge unlike neuronal cells. These two findings can possibly explain why muscle atrophy precedes the death of motor neurons in f-ALS mice.

Genetic ablation of 12/15-lipoxygenase but not 5-lipoxygenase protects against denervation-induced muscle atrophy.

Skeletal muscle atrophy is a debilitating outcome of a number of chronic diseases and conditions associated with loss of muscle innervation by motor neurons, such as aging and neurodegenerative diseases. We previously reported that denervation-induced loss of muscle mass is associated with activation of cytosolic phospholipase A2 (cPLA2), the rate-limiting step for the release of arachidonic acid from membrane phospholipids, which then acts as a substrate for metabolic pathways that generate bioactive lipid mediators. In this study, we asked whether 5- and 12/15-lipoxygenase (LO) lipid metabolic pathways downstream of cPLA2 mediate denervation-induced muscle atrophy in mice. Both 5- and 12/15-LO were activated in response to surgical denervation; however, 12/15-LO activity was increased ~2.5-fold versus an ~1.5-fold increase in activity of 5-LO. Genetic and pharmacological inhibition of 12/15-LO (but not 5-LO) significantly protected against denervation-induced muscle atrophy, suggesting a selective role for the 12/15-LO pathway in neurogenic muscle atrophy. The activation of the 12/15-LO pathway (but not 5-LO) during muscle atrophy increased NADPH oxidase activity, protein ubiquitination, and ubiquitin-proteasome-mediated proteolytic degradation. In conclusion, this study reveals a novel pathway for neurogenic muscle atrophy and suggests that 12/15-LO may be a potential therapeutic target in diseases associated with loss of innervation and muscle atrophy.

Differential effects of mutant SOD1 on protein structure of skeletal muscle and spinal cord of familial amyotrophic lateral sclerosis: role of chaperone network.

Protein misfolding is considered to be a potential contributing factor for motor neuron and muscle loss in diseases like Amyotrophic lateral sclerosis (ALS). Several independent studies have demonstrated using over-expressed mutated Cu/Zn-superoxide dismutase (mSOD1) transgenic mouse models which mimic familial ALS (f-ALS), that both muscle and motor neurons undergo degeneration during disease progression. However, it is unknown whether protein conformation of skeletal muscle and spinal cord is equally or differentially affected by mSOD1-induced toxicity. It is also unclear whether heat shock proteins (Hsp's) differentially modulate skeletal muscle and spinal cord protein structure during ALS disease progression. We report three intriguing observations utilizing the f-ALS mouse model and cell-free in vitro system; (i) muscle proteins are equally sensitive to misfolding as spinal cord proteins despite the presence of low level of soluble and absence of insoluble G93A protein aggregate, unlike in spinal cord, (ii) Hsp's levels are lower in muscle compared to spinal cord at any stage of the disease, and (iii) G93ASOD1 enzyme-induced toxicity selectively affects muscle protein conformation over spinal cord proteins. Together, these findings strongly suggest that differential chaperone levels between skeletal muscle and spinal cord may be a critical determinant for G93A-induced protein misfolding in ALS.

CuZnSOD gene deletion targeted to skeletal muscle leads to loss of contractile force but does not cause muscle atrophy in adult mice.

We have previously shown that deletion of CuZnSOD in mice (Sod1(-/-) mice) leads to accelerated loss of muscle mass and contractile force during aging. To dissect the relative roles of skeletal muscle and motor neurons in this process, we used a Cre-Lox targeted approach to establish a skeletal muscle-specific Sod1-knockout (mKO) mouse to determine whether muscle-specific CuZnSOD deletion is sufficient to cause muscle atrophy. Surprisingly, mKO mice maintain muscle masses at or above those of wild-type control mice up to 18 mo of age. In contrast, maximum isometric specific force measured in gastrocnemius muscle is significantly reduced in the mKO mice. We found no detectable increases in global measures of oxidative stress or ROS production, no reduction in mitochondrial ATP production, and no induction of adaptive stress responses in muscle from mKO mice. However, Akt-mTOR signaling is elevated and the number of muscle fibers with centrally located nuclei is increased in skeletal muscle from mKO mice, which suggests elevated regenerative pathways. Our data demonstrate that lack of CuZnSOD restricted to skeletal muscle does not lead to muscle atrophy but does cause muscle weakness in adult mice and suggest loss of CuZnSOD may potentiate muscle regenerative pathways.

Elevated protein carbonylation, and misfolding in sciatic nerve from db/db and Sod1(-/-) mice: plausible link between oxidative stress and demyelination.

Diabetic peripheral polyneuropathy is associated with decrements in motor/sensory neuron myelination, nerve conduction and muscle function; however, the mechanisms of reduced myelination in diabetes are poorly understood. Chronic elevation of oxidative stress may be one of the potential determinants for demyelination as lipids and proteins are important structural constituents of myelin and highly susceptible to oxidation. The goal of the current study was to determine whether there is a link between protein oxidation/misfolding and demyelination. We chose two distinct models to test our hypothesis: 1) the leptin receptor deficient mouse (dbdb) model of diabetic polyneuropathy and 2) superoxide dismutase 1 knockout (Sod1(-/-) ) mouse model of in vivo oxidative stress. Both experimental models displayed a significant decrement in nerve conduction, increase in tail distal motor latency as well as reduced myelin thickness and fiber/axon diameter. Further biochemical studies demonstrated that oxidative stress is likely to be a potential key player in the demyelination process as both models exhibited significant elevation in protein carbonylation and alterations in protein conformation. Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice. Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice. Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice. Collectively, these data strongly suggest for the first time that oxidation-mediated protein misfolding and aggregation of key myelin proteins may be linked to demyelination and reduced nerve conduction in peripheral neuropathies.

Reduced mitochondrial ROS, enhanced antioxidant defense, and distinct age-related changes in oxidative damage in muscles of long-lived Peromyscus leucopus.

Comparing biological processes in closely related species with divergent life spans is a powerful approach to study mechanisms of aging. The oxidative stress hypothesis of aging predicts that longer-lived species would have lower reactive oxygen species (ROS) generation and/or an increased antioxidant capacity, resulting in reduced oxidative damage with age than in shorter-lived species. In this study, we measured ROS generation in the young adult animals of the long-lived white-footed mouse, Peromyscus leucopus (maximal life span potential, MLSP = 8 yr) and the common laboratory mouse, Mus musculus (C57BL/6J strain; MLSP = 3.5 yr). Consistent with the hypothesis, our results show that skeletal muscle mitochondria from adult P. leucopus produce less ROS (superoxide and hydrogen peroxide) compared with M. musculus. Additionally, P. leucopus has an increase in the activity of antioxidant enzymes superoxide dismutase 1, catalase, and glutathione peroxidase 1 at young age. P. leucopus compared with M. musculus display low levels of lipid peroxidation (isoprostanes) throughout life; however, P. leucopus although having elevated protein carbonyls at a young age, the accrual of protein oxidation with age is minimal in contrast to the linear increase in M. musculus. Altogether, the results from young animals are in agreement with the predictions of the oxidative stress hypothesis of aging with the exception of protein carbonyls. Nonetheless, the age-dependent increase in protein carbonyls is more pronounced in short-lived M. musculus, which supports enhanced protein homeostasis in long-lived P. leucopus.