Hindlimb immobilization induces insulin resistance and elevates mitochondrial ROS production in the hippocampus of female rats.

Alzheimer's Disease (AD) is the 5th leading cause of death in older adults and treatment options are severely lacking. Recent findings demonstrate a strong relationship between skeletal muscle and cognitive function, with evidence supporting that muscle quality and cognitive function are positively correlated in older adults. Conversely, decreased muscle function is associated with a 3-fold increased risk of cognitive decline. Based on these observations, the purpose of this study was to investigate the negative effects of muscle disuse (via a model of hindlimb immobilization (HLI)) on hippocampal insulin sensitivity and mitochondrial function and identify the potential mechanisms involved. HLI for 10 days in 4-month-old female Wistar rats resulted in the following novel findings: 1) hippocampal insulin resistance and deficits in whole body glucose homeostasis, 2) dramatically increased mitochondrial reactive oxygen species (ROS) production in the hippocampus, 3) elevated markers for amyloidogenic cleavage of APP and tau protein in the hippocampus, 4) and reduced BDNF expression. These findings were associated with global changes in iron homeostasis, with muscle disuse producing muscle iron accumulation in association with decreased serum and whole brain iron levels. We report the novel finding that muscle disuse alters brain iron homeostasis and reveal a strong negative correlation between muscle and brain iron content. Overall, HLI-induced muscle disuse has robust negative effects on hippocampal insulin sensitivity and ROS production in association with altered brain iron homeostasis. This work provides potential novel mechanisms that may help explain how loss of muscle function contributes to cognitive decline and AD risk.

Body mass index stratification enables cytokine-based prediction of ACPA status and Power-Doppler disease activity in rheumatoid arthritis.

OBJECTIVE: Rheumatoid arthritis can be classified according to ACPA and RF status. ACPA status may be associated with other pathophysiological differences, e.g., the cytokines driving inflammation. Obesity influences the course of RA, likely involving leptin; the exact mechanisms are not completely understood. This study investigates BMI influence on RA cytokine profiles and the possibility of predicting ACPA status and disease activity measured by Power-Doppler sonography (PDS). METHODS: Patients were examined using a multi-biomarker disease assay and PDS examination of wrists and MCP and PIP joints and stratified according to ACPA status and BMI, using prediction precision to determine BMI cutoff. Analysis was performed using elastic net regularization of logistic and multiple regression. We then attempted to predict ACPA status/PDS activity based on a bootstrap approach. RESULTS: A total of 120 measurements from 95 patients were performed. ACPA status prediction peaked at BMI 26 kg/m2, with AUC 0.82. PDS activity prediction had a mean average error of < 1.6 PDS points for all groups. In obese patients, cytokine profiles appear to align in ACPA-positive and -negative patients, with leptin playing a greater role in predicting PDS activity, but with some remaining differences. CONCLUSION: When stratified according to BMI, cytokine patterns can predict ACPA status and PDS activity in RA with a high degree of precision. This indicates that studies into the pathophysiology of RA should take BMI into account, to differentiate between disease- and obesity-associated phenomena. The underlying pathological processes of ACPA-negative and -positive RA appear different. Multi-cytokine evaluations may provide a deeper understanding of disease processes. Key Points • A multi-cytokine approach combined with ultrasonography and modern mathematical methods can contribute to a deeper understanding of the relationship between systemic and joint inflammation. • BMI influences cytokine profiles in rheumatoid arthritis and appears to "override" disease-specific processes. • Using cytokines only, and adjusting for BMI, it is possible to predict the ACPA status and joint inflammation with considerable precision.

Sodium Phenylbutyrate and Tauroursodeoxycholic Acid: A Story of Hope Turned to Disappointment in Amyotrophic Lateral Sclerosis Treatment.

The absence of a definitive cure for amyotrophic lateral sclerosis (ALS) emphasizes the crucial need to explore new and improved treatment approaches for this fatal, progressive, and disabling neurodegenerative disorder. As at the end of 2023, five treatments - riluzole, edaravone, dextromethorphan hydrobromide + quinidine sulfate (DHQ), tofersen, and sodium phenylbutyrate-tauroursodeoxycholic acid (PB-TUDCA) - were FDA approved for the treatment of patients with ALS. Among them PB-TUDCA has been shown to impact DNA processing impairments, mitochondria dysfunction, endoplasmic reticulum stress, oxidative stress, and pathologic folded protein agglomeration defects, which have been associated with ALS pathophysiology. The Phase 2 CENTAUR trial demonstrated significant impact of PB-TUDCA on the ALS Functional Rating Scale-Revised (ALSFRS-R) risk of death, hospitalization, and the need for tracheostomy or permanent assisted ventilation in patients with ALS based on post hoc analyses. More recently, contrasting with the CENTAUR trial results, results from the Phase 3 PHOENIX trial (NCT05021536) showed no change in ALSFRS-R total score at 48 weeks. Consequently, the sponsor company initiated the process with the US FDA and Health Canada to voluntarily withdraw the marketing authorizations for PB-TUDCA. In the present article, we review ALS pathophysiology, with a focus on PB-TUDCA's proposed mechanisms of action and recent clinical trial results and discuss the implications of conflicting trial data for ALS and other neurological disorders.

Effects of a ketogenic diet on motor function and motor unit number estimation in aged C57BL/6 mice.

OBJECTIVE: Pathological, age-related loss of muscle function, commonly referred to as sarcopenia, contributes to loss of mobility, impaired independence, as well as increased risk of adverse health events. Sarcopenia has been attributed to changes in both neural and muscular integrity during aging. Current treatment options are primarily limited to exercise and dietary protein fortification, but the therapeutic impact of these approaches are often inadequate. Prior work has suggested that a ketogenic diet (KD) might improve healthspan and lifespan in aging mice. Thus, we sought to investigate the effects of a KD on neuromuscular indices of sarcopenia in aged C57BL/6 mice. DESIGN: A randomized, controlled pre-clinical experiment consisting of longitudinal assessments performed starting at 22-months of age (baseline) as well as 2, 6 and 10 weeks after the start of a KD vs. regular chow intervention. SETTING: Preclinical laboratory study. SAMPLE SIZE: Thirty-six 22-month-old mice were randomized into 2 dietary groups: KD [n = 22 (13 female and 9 male)], and regular chow [n = 15 (7 female and 8 male)]. MEASUREMENTS: Measures included body mass, hindlimb and all limb grip strength, rotarod for motor performance, plantarflexion muscle contractility, motor unit number estimations (MUNE), and repetitive nerve stimulation (RNS) as an index of neuromuscular junction transmission efficacy recorded from the gastrocnemius muscle. At end point, muscle wet weight and blood samples were collected to assess blood beta-hydroxybutyrate levels. STATISTICAL ANALYSIS: Primary analyses were two-way mixed effects ANOVA (diet and time × diet) to determine the effect of a KD on indices of motor function (grip, rotarod) and indices of motor unit (MUNE) and muscle (contractility) function. RESULTS: Beta-hydroxybutyrate (BHB) was significantly higher at 10 weeks in mice on a KD vs control group (0.83 ± 0.44 mmol/l versus 0.42 ± 0.21 mmol/l, η2 = 0.265, unpaired t-test, p = 0.0060). Mice on the KD intervention demonstrated significantly increased hindlimb grip strength (diet, p = 0.0001; time × diet, p = 0.0030), all limb grip strength (diet, p = 0.0005; time × diet, p = 0.0523), and rotarod latency to fall (diet, p = 0.0126; time × diet, p = 0.0021). Mice treated with the KD intervention also demonstrated increased MUNE (diet, p = 0.0465; time × diet, p = 0.0064), but no difference in muscle contractility (diet, p = 0.5248; time × diet, p = 0.5836) or RNS (diet, p = 0.3562; time × diet, p = 0.9871). CONCLUSION: KD intervention improved neuromuscular and motor function in aged mice. This pre-clinical work suggests that further research is needed to assess the efficacy and physiological effects of a KD on indices of sarcopenia.

Differences in Psychological Health and Weight Loss after Bariatric Metabolic Surgery between Patients with and without Pain Syndromes.

PURPOSE: Chronic pain and obesity often co-occur, negatively affecting one another and psychological wellbeing. Pain and psychological wellbeing improve after bariatric metabolic surgery (BMS), however, it is unknown whether psychological wellbeing improves differently after weight loss between patients with and without chronic pain. We investigated whether weight loss is associated with greater psychological wellbeing and functioning change after BMS, comparing patients with and without preoperative pain syndromes. METHODS: Depression, health-related quality of life, self-esteem, self-efficacy to exercise and controlling eating behaviours, physical activity, and food cravings were measured before and 24 months after BMS among 276 patients with obesity. The presence of preoperative chronic pain syndromes was examined as a moderator for the relationship between 24-month weight loss and changes in psychological outcomes. RESULTS: Chronic pain syndromes were present among 46% of patients. Weight loss was associated with greater improvement in health-related quality of life, self-efficacy to exercise and controlling eating behaviours, self-esteem and greater amelioration in food cravings. Pain syndromes only moderated negatively the relationship between the postoperative weight loss and change in self-efficacy to control eating behaviours (b = -0.49, CI [-0.88,-0.12]). CONCLUSION: Patients with and without chronic pain showed similar improvements in weight and psychological wellbeing and behaviours after BMS. The relationship between weight loss and the improvement of self-efficacy to control eating behaviours was weaker among patients with chronic pain syndrome. Further work, measuring pain severity over time, is needed to shed light on the mechanism underlying pain and postoperative change in psychological wellbeing and weight loss.

YTHDF2 governs muscle size through a targeted modulation of proteostasis.

The regulation of proteostasis is fundamental for maintenance of muscle mass and function. Activation of the TGF-ß pathway drives wasting and premature aging by favoring the proteasomal degradation of structural muscle proteins. Yet, how this critical post-translational mechanism is kept in check to preserve muscle health remains unclear. Here, we reveal the molecular link between the post-transcriptional regulation of m6A-modified mRNA and the modulation of SMAD-dependent TGF-ß signaling. We show that the m6A-binding protein YTHDF2 is essential to determining postnatal muscle size. Indeed, muscle-specific genetic deletion of YTHDF2 impairs skeletal muscle growth and abrogates the response to hypertrophic stimuli. We report that YTHDF2 controls the mRNA stability of the ubiquitin ligase ASB2 with consequences on anti-growth gene program activation through SMAD3. Our study identifies a post-transcriptional to post-translational mechanism for the coordination of gene expression in muscle.

Stimulated Single Fiber Electromyography (SFEMG) for Assessing Neuromuscular Junction Transmission in Rodent Models.

As the final connection between the nervous system and muscle, transmission at the neuromuscular junction (NMJ) is crucial for normal motor function. Single fiber electromyography (SFEMG) is a clinically relevant and sensitive technique that measures single muscle fiber action potential responses during voluntary contractions or nerve stimulations to assess NMJ transmission. The assessment and quantification of NMJ transmission involves two parameters: jitter and blocking. Jitter refers to the variability in timing (latency) between consecutive single-fiber action potentials (SFAPs). Blocking signifies the failure of NMJ transmission to initiate an SFAP response. Although SFEMG is a well-established and sensitive test in clinical settings, its application in preclinical research has been relatively infrequent. This report outlines the steps and criteria employed in performing stimulated SFEMG to quantify jitter and blocking in rodent models. This technique can be used in preclinical and clinical studies to gain insights into NMJ function in the context of health, aging, and disease.

Variation in HbA1c in Patients with Obesity and type 2 Diabetes Mellitus 12 months after Laparoscopic One-Anastomosis Gastric Bypass and Laparoscopic Roux-en-Y Gastric Bypass: a Retrospective Matched Cohort Study.

BACKGROUND: Glycemic control is an important goal of bariatric surgery in patients with type 2 diabetes mellitus (T2DM) and obesity. The laparoscopic one-anastomosis gastric bypass (OAGB) has potential metabolic benefits over the laparoscopic Roux-en-Y gastric bypass (RYGB). Aim of this study is to examine whether RYGB or OAGB grants better glycemic control 12 months post-surgery. METHODS: For this retrospective cohort study, patients with T2DM and obesity, who underwent primary OAGB between 2008 and 2017 were reviewed. For each OAGB patient, three primary RYGB patients were matched for age, gender and body mass index (BMI). Glycemic control was expressed by the glycated hemoglobin (HbA1c), which was measured pre- and 12 months post-operatively. Weight loss was reported in percentage total weight loss (%TWL). RESULTS: A total of 152 patients, of whom 38 had OAGB and 114 RYGB, were included. Mean (standard deviation (SD)) HbA1c was 7.49 (1.51)% in the OAGB group and 7.56(1.23)% in the RYGB group at baseline. Twelve months after surgery the mean (SD) HbA1c dropped to 5.73 (0.71)% after OAGB and 6.09 (0.76)% after RYGB (adjusted p = 0.011). The mean (SD) BMI was reduced from 42.5(6.3) kg/m2 to 29.6(4.7) kg/m2 after OAGB and 42.3(5.8) kg/m2 to 29.9 (4.5) kg/m2 after RYGB; reflecting 30.3 (6.8) %TWL post-OAGB and 29.0 (7.3) %TWL post-RYGB (p = 0.34). CONCLUSION: This study indicates that OAGB leads to lower HbA1c one year after surgery compared to RYGB, without a difference in weight loss. Prospective (randomized) studies are needed to ascertain the most optimal metabolic treatment for patients with obesity and T2DM.

Contributions of mouse genetic strain background to age-related phenotypes in physically active HET3 mice.

We assessed aging hallmarks in skin, muscle, and adipose in the genetically diverse HET3 mouse, and generated a broad dataset comparing these to individual animal diagnostic SNPs from the 4 founding inbred strains of the HET3 line. For middle- and old-aged HET3 mice, we provided running wheel exercise to ensure our observations were not purely representative of sedentary animals, but age-related phenotypes were not improved with running wheel activity. Adipose tissue fibrosis, peripheral neuropathy, and loss of neuromuscular junction integrity were consistent phenotypes in older-aged HET3 mice regardless of physical activity, but aspects of these phenotypes were moderated by the SNP% contributions of the founding strains for the HET3 line. Taken together, the genetic contribution of founder strain SNPs moderated age-related phenotypes in skin and muscle innervation and were dependent on biological sex and chronological age. However, there was not a single founder strain (BALB/cJ, C57BL/6J, C3H/HeJ, DBA/2J) that appeared to drive more protection or disease-risk across aging in this mouse line, but genetic diversity in general was more protective.

Temporal changes in the positivity rate of common enteric viruses among paediatric admissions in coastal Kenya, during the COVID-19 pandemic, 2019-2022.

BACKGROUND: The non-pharmaceutical interventions (NPIs) implemented to curb the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) early in the coronavirus disease 2019 (COVID-19) pandemic, substantially disrupted the activity of other respiratory viruses. However, there is limited data from low-and-middle income countries (LMICs) to determine whether these NPIs also impacted the transmission of common enteric viruses. Here, we investigated the changes in the positivity rate of five enteric viruses among hospitalised children who presented with diarrhoea to a referral hospital in coastal Kenya, during COVID-19 pandemic period. METHODS: A total of 870 stool samples from children under 13 years of age admitted to Kilifi County Hospital between January 2019, and December 2022 were screened for rotavirus group A (RVA), norovirus genogroup II (GII), astrovirus, sapovirus, and adenovirus type F40/41 using real-time reverse-transcription polymerase chain reaction. The proportions positive across the four years were compared using the chi-squared test statistic. RESULTS: One or more of the five virus targets were detected in 282 (32.4%) cases. A reduction in the positivity rate of RVA cases was observed from 2019 (12.1%, 95% confidence interval (CI) 8.7-16.2%) to 2020 (1.7%, 95% CI 0.2-6.0%; p < 0.001). However, in the 2022, RVA positivity rate rebounded to 23.5% (95% CI 18.2%-29.4%). For norovirus GII, the positivity rate fluctuated over the four years with its highest positivity rate observed in 2020 (16.2%; 95% C.I, 10.0-24.1%). No astrovirus cases were detected in 2020 and 2021, but the positivity rate in 2022 was similar to that in 2019 (3.1% (95% CI 1.5%-5.7%) vs. 3.3% (95% CI 1.4-6.5%)). A higher case fatality rate was observed in 2021 (9.0%) compared to the 2019 (3.2%), 2020 (6.8%) and 2022 (2.1%) (p < 0.001). CONCLUSION: Our study finds that in 2020 the transmission of common enteric viruses, especially RVA and astrovirus, in Kilifi Kenya may have been disrupted due to the COVID-19 NPIs. After 2020, local enteric virus transmission patterns appeared to return to pre-pandemic levels coinciding with the removal of most of the government COVID-19 NPIs.

Preserving Endothelial Integrity in Human Saphenous Veins during Preparation for Coronary Bypass Surgery.

INTRODUCTION: While multiple factors influence coronary artery bypass graft (CABG) success rates, preserving saphenous vein endothelium during surgery may improve patency. Standard preparations include saphenous vein preparation in heparinized saline (saline) which can result in endothelial loss and damage. Here, we investigated the impact of preparing saphenous graft vessels in heparinized patient blood (blood) versus saline. METHODS: Saphenous vein tissues from a total of 23 patients undergoing CABG were split into 2 groups (1) saline and (2) heparinized patient blood. Excess tissue was fixed for analysis immediately following surgery. Level of endothelial coverage, oxidative stress marker 4-hydroxynonenal (4HNE), and oxidative stress protective marker nuclear factor erythroid 2-related factor 2 (NRF2) were evaluated. RESULTS: In saline patient veins, histological analysis revealed a limited luminal layer, suggesting a loss of endothelial cells (ECs). Immunofluorescent staining of EC markers vascular endothelial cadherin (VE-cadherin) and endothelial nitric oxide identified a significant improvement in EC coverage in the blood versus saline groups. Although both treatment groups expressed 4HNE to similar levels, EC blood samples expressed higher levels of NRF2. CONCLUSION: Our data indicate that use of heparinized patient blood helps preserve the endothelium and promotes vein graft health. This has the potential to improve long-term outcomes in patients.

Environmental Enrichment Improves Motor Function and Muscle Transcriptome of Aged Mice.

Aging results in the progressive decline of muscle strength. Interventions to maintain muscle strength may mitigate the age-related loss of physical function, thus maximizing health span. The work on environmental enrichment (EE), an experimental paradigm recapitulating aspects of an active lifestyle, has revealed EE-induced metabolic benefits mediated by a brain-fat axis across the lifespan of mice. EE initiated at 18-month of age shows a trend toward an increased mean lifespan. While previous work described EE's influences on the aging dynamics of several central-peripheral processes, its influence on muscle remained understudied. Here, the impact of EE is investigated on motor function, neuromuscular physiology, and the skeletal muscle transcriptome. EE is initiated in 20-month-old mice for a five-month period. EE mice exhibit greater relative lean mass that is associated with improved mobility and hindlimb grip strength. Transcriptomic profiling of muscle tissue reveals an EE-associated enrichment of gene expression within several metabolic pathways related to oxidative phosphorylation and the TCA cycle. Many mitochondrial-related genes-several of which participate in the electron transport chain-are upregulated. Stress-responsive signaling pathways are downregulated because of EE. The results suggest that EE improves motor function-possibly through preservation of mitochondrial function-even late in life.

Reductions in Motor Unit Firing are Associated with Clinically Meaningful Leg Extensor Weakness in Older Adults.

Weakness, one of the key characteristics of sarcopenia, is a significant risk factor for functional limitations and disability in older adults. It has long been suspected that reductions in motor unit firing rates (MUFRs) are one of the mechanistic causes of age-related weakness. However, prior work has not investigated the extent to which MUFR is associated with clinically meaningful weakness in older adults. Forty-three community-dwelling older adults (mean: 75.4 ± 7.4 years; 46.5% female) and 24 young adults (mean: 22.0 ± 1.8 years; 58.3% female) performed torque matching tasks at varying submaximal intensities with their non-dominant leg extensors. Decomposed surface electromyographic recordings were used to quantify MUFRs from the vastus lateralis muscle. Computational modeling was subsequently used to independently predict how slowed MUFRs would negatively impact strength in older adults. Bivariate correlations between MUFRs and indices of lean mass, voluntary activation, and physical function/mobility were also assessed in older adults. Weak older adults (n = 14) exhibited an approximate 1.5 and 3 Hz reduction in MUFR relative to non-weak older adults (n = 29) at 50% and 80% MVC, respectively. Older adults also exhibited an approximate 3 Hz reduction in MUFR relative to young adults at 80% MVC only. Our model predicted that a 3 Hz reduction in MUFR results in a strength decrement of 11-26%. Additionally, significant correlations were found between slower MUFRs and poorer neuromuscular quality, voluntary activation, chair rise time performance, and stair climb power (r's = 0.31 to 0.43). These findings provide evidence that slowed MUFRs are mechanistically linked with clinically meaningful leg extensor weakness in older adults.

Long-term effects of a fat-directed FGF21 gene therapy in aged female mice.

Fibroblast growth factor 21 (FGF21) has been developed as a potential therapeutic agent for metabolic syndromes. Moreover, FGF21 is considered a pro-longevity hormone because transgenic mice overexpressing FGF21 display extended lifespan, raising the possibility of using FGF21 to promote healthy aging. We recently showed that visceral fat directed FGF21 gene therapy improves metabolic and immune health in insulin resistant BTBR mice. Here, we used a fat directed rAAV-FGF21 vector in 17-month-old female mice to investigate whether long-term FGF21 gene transfer could mitigate aging-related functional decline. Animals with FGF21 treatment displayed a steady, significant lower body weight over 7-month of the study compared to age-matched control mice. FGF21 treatment reduced adiposity and increased relative lean mass and energy expenditure associated with almost 100 folds higher serum level of FGF21. However, those changes were not translated into benefits on muscle function and did not affect metabolic function of liver. Overall, we have demonstrated that a single dose of fat-directed AAV-FGF21 treatment can provide a sustainable, high serum level of FGF21 over long period of time, and mostly influences adipose tissue homeostasis and energy expenditure. High levels of FGF21 alone in aged mice is not sufficient to improve liver or muscle functions.

The burden of abdominal pain after bariatric surgery in terms of diagnostic testing: the OPERATE study.

BACKGROUND: Abdominal pain after bariatric surgery (BS) is frequently observed. Despite numerous diagnostic tests, the cause of abdominal pain is not always found. OBJECTIVES: To quantify type and number of diagnostic tests performed in patients with abdominal pain after BS and evaluate the burden and their yield in the diagnostic process. SETTING: A bariatric center in the Netherlands. METHODS: In this prospective study, we included patients who presented with abdominal pain after BS between December 1, 2020, and December 1, 2021. All diagnostic tests and reoperations performed during one episode of abdominal pain were scored using a standardized protocol. RESULTS: A total of 441 patients were included; 401 (90.9%) were female, median time after BS was 37.0 months (IQR, 11.0-66.0) and mean percentage total weight loss was 31.41 (SD, 10.53). In total, 715 diagnostic tests were performed, of which 355 were abdominal CT scans, 155 were ultrasounds, and 106 were gastroscopies. These tests yielded a possible explanation for the pain in 40.2% of CT scans, 45.3% of ultrasounds, and 34.7% of gastroscopies. The diagnoses of internal herniation, ileus, and nephrolithiasis generally required only 1 diagnostic test, whereas patients with anterior cutaneous nerve entrapment syndrome, irritable bowel syndrome, and constipation required several tests before diagnosis. Even after several negative tests, a diagnosis was still found in the subsequent test: 86.7% of patients with 5 or more tests had a definitive diagnoses. Reoperations were performed in 37.2% of patients. CONCLUSION: The diagnostic burden in patients with abdominal pain following BS is high. The most frequently performed diagnostic test is an abdominal CT scan, yielding the highest number of diagnoses in these patients.

Lesion level-dependent systemic muscle wasting after spinal cord injury is mediated by glucocorticoid signaling in mice.

An incomplete mechanistic understanding of skeletal muscle wasting early after spinal cord injury (SCI) precludes targeted molecular interventions. Here, we demonstrated systemic wasting that also affected innervated nonparalyzed (supralesional) muscles and emerged within 1 week after experimental SCI in mice. Systemic muscle wasting caused muscle weakness, affected fast type 2 myofibers preferentially, and became exacerbated after high (T3) compared with low (T9) thoracic paraplegia, indicating lesion level-dependent ("neurogenic") mechanisms. The wasting of nonparalyzed muscle and its rapid onset and severity beyond what can be explained by disuse implied unknown systemic drivers. Muscle transcriptome and biochemical analysis revealed a glucocorticoid-mediated catabolic signature early after T3 SCI. SCI-induced systemic muscle wasting was mitigated by (i) endogenous glucocorticoid ablation (adrenalectomy) and (ii) pharmacological glucocorticoid receptor (GR) blockade and was (iii) completely prevented after T3 relative to T9 SCI by genetic muscle-specific GR deletion. These results suggest that neurogenic hypercortisolism contributes to a rapid systemic and functionally relevant muscle wasting syndrome early after paraplegic SCI in mice.

The MuSK-BMP pathway regulates synaptic Nav1.4 localization and muscle excitability.

The neuromuscular junction (NMJ) is the linchpin of nerve-evoked muscle contraction. Broadly considered, the function of the NMJ is to transduce a nerve action potential into a muscle fiber action potential (MFAP). Efficient information transfer requires both cholinergic signaling, responsible for the generation of endplate potentials (EPPs), and excitation, the activation of postsynaptic voltage-gated sodium channels (Nav1.4) to trigger MFAPs. In contrast to the cholinergic apparatus, the signaling pathways that organize Nav1.4 and muscle fiber excitability are poorly characterized. Muscle-specific kinase (MuSK), in addition to its Ig1 domain-dependent role as an agrin-LRP4 receptor, is also a BMP co-receptor that binds BMPs via its Ig3 domain and shapes BMP-induced signaling and transcriptional output. Here we probed the function of the MuSK-BMP pathway at the NMJ using mice lacking the MuSK Ig3 domain ('ΔIg3-MuSK'). Synapses formed normally in ΔIg3-MuSK animals, but the postsynaptic apparatus was fragmented from the first weeks of life. Anatomical denervation was not observed at any age examined. Moreover, spontaneous and nerve-evoked acetylcholine release, AChR density, and endplate currents were comparable to WT. However, trains of nerve-evoked MFAPs in ΔIg3-MuSK muscle were abnormal as revealed by increased jitter and blocking in single fiber electromyography. Further, nerve-evoked compound muscle action potentials (CMAPs), as well as twitch and tetanic muscle torque force production, were also diminished. Finally, Nav1.4 levels were reduced at ΔIg3-MuSK synapses but not at the extrajunctional sarcolemma, indicating that the observed excitability defects are the result of impaired localization of this voltage-gated ion channel at the NMJ. We propose that MuSK plays two distinct roles at the NMJ: as an agrin-LRP4 receptor necessary for establishing and maintaining cholinergic signaling, and as a BMP co-receptor required for maintaining proper Nav1.4 density, nerve-evoked muscle excitability and force production. The MuSK-BMP pathway thus emerges as a target for modulating excitability and functional innervation, which are defective in conditions such as congenital myasthenic syndromes and aging.

Ketogenic Diet Improves Motor Function and Motor Unit Connectivity in Aged C57BL/6 Mice.

Objective: Pathological, age-related loss of muscle function, commonly referred to as sarcopenia, contributes to loss of mobility, impaired independence, as well as increased risk of adverse health events. Sarcopenia has been attributed to changes in both neural and muscular integrity during aging. Current treatment options are primarily limited to exercise and dietary protein fortification, but the therapeutic impact of these approaches are often inadequate. Prior work has suggested that a ketogenic diet (KD) might improve healthspan and lifespan in aging mice. Thus, we sought to investigate the effects of a KD on neuromuscular indices of sarcopenia in aged C57BL/6 mice. Design: A randomized, controlled pre-clinical experiment consisting of longitudinal assessments performed starting at 22-months of age (baseline) as well as 2, 6 and 10 weeks after the start of a KD vs. regular chow intervention. Setting: Preclinical laboratory study. Sample size: Thirty-six 22-month-old mice were randomized into 2 dietary groups: KD [n = 22 (13 female and 9 male)], and regular chow [n = 15 (7 female and 8 male)]. Measurements: Measures included body mass, hindlimb and all limb grip strength, rotarod for motor performance, plantarflexion muscle contractility, motor unit number estimations (MUNE), and repetitive nerve stimulation (RNS) as an index of neuromuscular junction transmission efficacy recorded from the gastrocnemius muscle. At end point, blood samples were collected to assess blood beta-hydroxybutyrate levels. Statistical Analysis: Two-way ANOVA mixed-effects analysis (time x diet) were performed to analyze grip, rotarod, MUNE, and muscle contractility data. Results: Beta-hydroxybutyrate (BHB) was significantly higher at 10 weeks in mice on a KD vs control group (0.83 ± 0.44 mmol/l versus 0.42 ± 0.21 mmol/l, η2 = 0.265, unpaired t-test, p = 0.0060). Mice on the KD intervention demonstrated significantly increased hindlimb grip strength (time x diet, p = 0.0030), all limb grip strength (time x diet, p = 0.0523), and rotarod latency to fall (time x diet, p = 0.0021). Mice treated with the KD intervention also demonstrated significantly greater MUNE (time x diet, p = 0.0064), but no difference in muscle contractility (time x diet, p = 0.5836) or RNS (time x diet, p = 0.9871). Conclusion: KD intervention improved neuromuscular and motor function in aged mice. This pre-clinical work suggests that further research is needed to assess the efficacy and physiological effects of a KD on indices of sarcopenia.

New SARS-CoV-2 Omicron Variant with Spike Protein Mutation Y451H, Kilifi, Kenya, March-May 2023.

We report a newly emerged SARS-CoV-2 Omicron subvariant FY.4 that has mutations Y451H in spike and P42L in open reading frame 3a proteins. FY.4 emergence coincided with increased SARS-CoV-2 cases in coastal Kenya during April-May 2023. Continued SARS-CoV-2 genomic surveillance is needed to identify new lineages to inform COVID-19 outbreak prevention.