Metabolomic profiling reveals muscle metabolic changes following iliac arteriovenous fistula creation in mice

Muscle PGC-1α Overexpression Drives Metabolite Secretion Boosting Subcutaneous Adipocyte Browning

Muscle and adipose tissue (AT) are in mutual interaction through the integration of endocrine and biochemical signals, thus regulating whole-body function and physiology. Besides a traditional view of endocrine relationships that imply the release of cytokines and growth factors, it is becoming increasingly clear that a metabolic network involving metabolites as signal molecules also exists between the two tissues. By elevating the number and functionality of mitochondria, a key role in muscle metabolism is played by the master regulator of mitochondrial biogenesis peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC-1α), that induces a fiber type shift from glycolytic to oxidative myofibers. As a consequence, the upregulation of muscle respiratory rate might affect metabolite production and consumption. However, the underlying mechanisms have not yet been fully elucidated. Here, we used a muscle-specific PGC-1α overexpressing mouse model (MCK-PGC-1α) to analyze the metabolite secretion profile of serum and culture medium recovered from MCK-PGC-1α muscle fibers by NMR. We revealed modified levels of different metabolites that might be ascribed to the metabolic activation of the skeletal muscle fibers. Notably, the dysregulated levels of these metabolites affected adipocyte differentiation, as well as the browning process in vitro and in vivo. Interestingly such effect was exacerbated in the subcutaneous WAT, while only barely present in the visceral WAT. Our data confirm a prominent role of PGC-1α as a trigger of mitochondrial function in skeletal muscle and propose a novel function of this master regulator gene in modulating the metabolite production in turn affecting the activation of WAT and its conversion toward the browning.

Mitochondrial targeted catalase improves muscle strength following arteriovenous fistula creation in mice with chronic kidney disease

Hand dysfunction is a common observation after arteriovenous fistula (AVF) creation for hemodialysis access and has a variable clinical phenotype; however, the underlying mechanism responsible is unclear. Grip strength changes are a common metric used to assess AVF-associated hand disability but has previously been found to poorly correlate with the hemodynamic perturbations post-AVF placement implicating other tissue-level factors as drivers of hand outcomes. In this study, we sought to test if expression of a mitochondrial targeted catalase (mCAT) in skeletal muscle could reduce AVF-related limb dysfunction in mice with chronic kidney disease (CKD). Male and female C57BL/6J mice were fed an adenine-supplemented diet to induce CKD prior to placement of an AVF in the iliac vascular bundle. Adeno-associated virus was used to drive expression of either a green fluorescent protein (control) or mCAT using the muscle-specific human skeletal actin (HSA) gene promoter prior to AVF creation. As expected, the muscle-specific AAV-HSA-mCAT treatment did not impact blood urea nitrogen levels (P = 0.72), body weight (P = 0.84), or central hemodynamics including infrarenal aorta and inferior vena cava diameters (P > 0.18) or velocities (P > 0.38). Hindlimb perfusion recovery and muscle capillary densities were also unaffected by AAV-HSA-mCAT treatment. In contrast to muscle mass and myofiber size which were not different between groups, both absolute and specific muscle contractile forces measured via a nerve-mediated in-situ preparation were significantly greater in AAV-HSA-mCAT treated mice (P = 0.0012 and P = 0.0002). Morphological analysis of the post-synaptic neuromuscular junction uncovered greater acetylcholine receptor cluster areas (P = 0.0094) and lower fragmentation (P = 0.0010) in AAV-HSA-mCAT treated mice. Muscle mitochondrial oxidative phosphorylation was not different between groups, but AAV-HSA-mCAT treated mice had lower succinate-fueled mitochondrial hydrogen peroxide emission compared to AAV-HSA-GFP mice (P < 0.001). In summary, muscle-specific scavenging of mitochondrial hydrogen peroxide significantly improves neuromotor function in mice with CKD following AVF creation.

Temporal serum metabolomic and lipidomic analyses distinguish patients with access-related hand disability following arteriovenous fistula creation

For end-stage kidney disease (ESKD) patients, hemodialysis requires durable vascular access which is often surgically created using an arteriovenous fistula (AVF). However, some ESKD patients that undergo AVF placement develop access-related hand dysfunction (ARHD) through unknown mechanisms. In this study, we sought to determine if changes in the serum metabolome could distinguish ESKD patients that develop ARHD from those that have normal hand function following AVF creation. Forty-five ESKD patients that underwent first-time AVF creation were included in this study. Blood samples were obtained pre-operatively and 6-weeks post-operatively and metabolites were extracted and analyzed using nuclear magnetic resonance spectroscopy. Patients underwent thorough examination of hand function at both timepoints using the following assessments: grip strength manometry, dexterity, sensation, motor and sensory nerve conduction testing, hemodynamics, and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire. Nineteen of the forty-five patients displayed overt weakness using grip strength manometry (P < 0.0001). Unfortunately, the serum metabolome was indistinguishable between patients with and without weakness following AVF surgery. However, a significant correlation was found between the change in tryptophan levels and the change in grip strength suggesting a possible role of tryptophan-derived uremic metabolites in post-AVF hand-associated weakness. Compared to grip strength, changes in dexterity and sensation were smaller than those observed in grip strength, however, post-operative decreases in phenylalanine, glycine, and alanine were unique to patients that developed signs of motor or sensory disability following AVF creation.