Naddaf, Elie

ABSTRACT Introduction/Aims Phrenic nerve conduction studies (NCS) are regularly used in the evaluation of neuromuscular respiratory dysfunction; however, the impact of body mass index (BMI) on phrenic compound muscle action potential (CMAP) amplitudes remains poorly characterized. We evaluated the relationship between BMI and phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Methods We performed a retrospective secondary analysis of patients derived from two previously published cohorts from Mayo Clinic (Rochester, Minnesota) and the University of Alberta (Edmonton, Alberta) evaluating diaphragm ultrasound in suspected neuromuscular respiratory insufficiency. Patients without evidence of neuromuscular disease affecting the diaphragm who underwent bilateral phrenic NCS and diaphragm ultrasound were included. Results Seventy‐nine patients met inclusion criteria, including 36 with BMI ≥ 30 kg/m 2 . Median phrenic CMAP amplitudes were significantly lower in patients with BMI ≥ 30 kg/m 2 compared to BMI < 30 kg/m 2 (0.25 mV [ IQR 0.10–0.38] vs. 0.50 mV [0.30–0.65], p < 0.001). Low phrenic CMAP amplitudes (< 0.3 mV ) were more common in patients with obesity (58% vs. 21%, p < 0.001). BMI demonstrated a moderate negative correlation with phrenic CMAP amplitude ( ρ = −0.50, p < 0.001). Diaphragm thickness at functional residual capacity did not differ significantly between BMI groups, while diaphragm thickening ratio was modestly lower in obesity. Discussion Elevated BMI is associated with lower phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Reduced phrenic CMAP amplitudes in obesity may reflect technical recording limitations rather than clinically meaningful diaphragmatic dysfunction. Low‐amplitude phrenic responses in patients with obesity should be interpreted cautiously and alongside adjunctive assessments such as diaphragm ultrasound.

Abstract Oxidative phosphorylation (OXPHOS) is a central function and a key indicator of mitochondrial fitness, yet studies in human tissue remain limited. Inclusion body myositis (IBM) is a progressive myopathy that lies at the intersection of aging, inflammation and mitochondrial dysfunction. We aimed to perform a comprehensive profiling of mitochondrial respiration in muscle tissue from patients with IBM. A wide battery of complementary approaches from RNA level to high-resolution respirometry on permeabilized muscle fibers was employed. The relationship between mitochondrial respiration, mitochondrial content, mitochondrial DNA (mtDNA) abnormalities and mitophagy was examined, along with the correlation with various clinical parameters to determine their clinical relevance. The study included a total of 67 patients with IBM and 45 controls. On high resolution respirometry of permeabilized muscle fibers, IBM samples exhibited reduced maximal mitochondrial respiration per tissue weight in State 3 (high substrates, high ADP) and uncoupled state with decreased coupling efficiency and higher leak control ratios. When adjusting for citrate synthase reflecting mitochondrial content, male patients had decreased State 3 intrinsic respiration, whereas female patients had greater intrinsic respiration under leak states. Complex I activity was decreased mainly in female patients, in whom complex II control ratio positively correlated with disease duration and severity. IBM was further associated with decreased RNA levels of all complexes, and lower protein expression of complex I, III, IV and V, likely related to the lower mtDNA content seen in IBM samples. Regarding the production of reactive oxygen species, IBM samples exhibited lower maximal H2O2 emission, accompanied by a higher total antioxidant capacity that positively correlated with disease duration in female patients. Lastly, correlation analyses suggested that impaired mitochondrial respiration, altered mitophagy, and reduced mtDNA content are interconnected in IBM and maybe of clinical significance. IBM is characterized by multifaceted, clinically relevant impairments in mitochondrial respiration. Future studies should further explore underlying pathomechanisms and the variation of mitochondrial respiration by disease stage.

Abstract Sarcomeres are the fundamental functional units of skeletal muscle, essential for both force generation and metabolic homeostasis. While sarcomere degradation has been extensively studied, the mechanisms that preserve its integrity remain poorly defined. Here, we identify HECTD1 as an E3 ubiquitin ligase required for sarcomere maintenance and mitochondrial integrity. We show that HECTD1 ubiquitylates and stabilizes the chaperones KLHL40/41, which protect thin-filament components from misfolding and degradation. Consequently, reducing Hectd1 expression in myotubes coordinately decreases the levels of multiple sarcomere proteins. Skeletal muscle–specific Hectd1 knockout mice ( Hectd1 mKO) show severe sarcomere and mitochondrial disorganization and dysfunction, progressive muscle weakness, exercise and glucose intolerance, and unresolved tissue remodeling. Importantly, human iPSC-derived myotubes carrying a patient-associated HECTD1 mutation, recapitulate key molecular features of the Hectd1 mKO. These findings establish HECTD1 as a central regulator linking sarcomere proteostasis to mitochondrial function and identify its dysfunction as a cause of myopathy with mitochondriopathy.

ABSTRACT Autoantibody internalization has been implicated in autoimmune disease pathogenesis, yet its mechanisms, and generality across different diseases, cell types, and affected tissues remain poorly defined. Using bulk RNA sequencing, we identified reproducible, autoantibody-specific transcriptomic signatures consistent with autoantigen dysfunction in muscle biopsies from patients with anti-Mi2 dermatomyositis and anti-PM/Scl scleromyositis across independent cohorts. Electroporation of purified patient IgG into primary cultures of healthy cells was sufficient to induce the corresponding transcriptomic programs in vitro . Direct immunofluorescence demonstrated immunoglobulin internalization into subcellular compartments matching the localization of the autoantigen in different affected tissues. Spatial transcriptomic analyses revealed that antibody-secreting cells translocated cytoplasmic material (i.e., immunoglobulin RNA) into adjacent affected cells expressing autoantibody-specific transcripts. The disease-specific transcripts were present not only in muscle fibers, but also in other cells, including macrophages, endothelial cells, and fibroblasts. Autoantibody-induced transcriptomic programs were associated with cell damage and autoantibody-specific reactive inflammatory programs, including activation of type I interferon and TGF-ß1 signaling in anti-Mi2 dermatomyositis and activation of type II interferon in anti-PM/Scl scleromyositis. Antibody internalization was also observed in different tissues from patients with other autoimmune diseases, including anti-U1RNP mixed connective tissue disease, anti-Ku overlap syndrome, and anti-Scl70 systemic sclerosis. Together, these findings establish autoantibody internalization as a shared pathogenic mechanism across diverse autoimmune diseases, providing a unifying framework for conditions driven by autoantibodies against intracellular antigens.

Abstract Objective Myositis is a heterogeneous family of inflammatory myopathies. We sought to define the differential expression of cytokines, cytokine receptors and immune checkpoint genes in muscle biopsies from patients with different forms of myositis in order to characterize patterns of inflammation in each. Methods Bulk RNA-sequencing was performed on muscle biopsy samples from 669 patients, including 105 with DM, 80 with immune-mediated necrotizing myopathy (IMNM), 65 with anti-synthetase syndrome, 53 with IBM, 19 with anti-PM/Scl myositis, 310 with other inflammatory or genetic myopathies and 37 controls with normal tissue (NT). Myositis clinical groups and autoantibody subgroups were analysed separately. Expression data were analysed for 338 genes encoding cytokines, cytokine receptors and immune checkpoints. Myositis group-specific genes were identified from this list by finding genes that were specifically differentially expressed in one group compared with all samples and compared with NT (α &lt; 0.001). Results IBM patients had the most differentially overexpressed genes (71) among all clinical groups, including 37 that were IBM-specific. Among the top genes were several involved in type 1 inflammation, including CCL5, CXCR3, CCR5, CXCL9 and IFNG. Anti-Jo1 and anti-PM/Scl patients exhibited differential overexpression of a similar set of genes, while DM patients exhibited differential overexpression of a different set of genes involved in type 1 inflammation. IMNM patients had the least number of differentially overexpressed genes with no predominant inflammatory pattern. Conclusion Each myositis clinical group and autoantibody subgroup had differentially overexpressed inflammatory mediators, including a strong type 1 inflammatory gene signature in IBM.

ABSTRACTBackgroundIdiopathic inflammatory myopathies, beyond inclusion body myositis (IBM), have demonstrated an increased risk of adverse cardiovascular outcomes, particularly myocardial infarction (MI). This study evaluated the risk of cardiovascular disease in IBM.MethodsWe conducted a non‐concurrent cohort study utilizing the expanded Rochester Epidemiologic Project, including 50 patients with IBM, matched 1:6 to age‐, sex‐, and calendar year‐matched referents without IBM. Baseline cardiovascular risk factors were recorded. Differences in baseline covariates were adjusted by the inverse probability of treatment weighting method. Participants were followed from the index date forward to determine relative risks (RR) and hazard ratios (HR) for the development of cardiovascular outcomes including MI, ischemic stroke, cardiomyopathy, congestive heart failure (CHF), and peripheral vascular disease (PVD).Results50 patients with IBM and 294 matched population referents were included. Baseline cardiovascular risk factors were similar between groups. Aspirin use was more common (28% vs. 18%, p = 0.03) and statin use less common (26% vs. 38%, p = 0.04) in IBM versus referents. Patients with IBM had an increased hazard of MI compared to referents [HR: 5.79, 95% CI (2.51, 13.36)]. The risk of MI remained consistently elevated across all models, after accounting for potential confounders. For PVD, 16/50 IBM patients versus 16/287 referents were excluded due to pre‐existing PVD at index (p < 0.001). Among remaining participants, RR for PVD was 2.38 (0.82, 6.9). IBM was not associated with an increased risk of ischemic stroke, cardiomyopathy, or CHF.ConclusionsIBM is associated with increased risk of MI compared to population referents. Heightened cardiovascular monitoring and prevention strategies are needed in IBM.

Abstract Objectives IBM is characterized by slowly progressive muscle weakness making it challenging to detect significant changes in weakness during a clinical trial. Trial participants receiving placebo may behave differently from in natural history studies. We aimed to quantify the change in muscle strength and IBM Functional Rating Scale (IBMFRS) of IBM patients receiving placebo during clinical trials. Methods Several databases were searched. Randomized, double-blinded, placebo-controlled trials without treatment intervention on the placebo group were included. Standardized mean differences (SMD) for change in muscle strength and mean differences for IBMFRS were used to calculate pooled effects, using DerSimonian-Laird continuous random effect models. Meta-regression determined change in muscle strength. Heterogeneity was evaluated using the I2 indicator. Results Eleven eligible trials were identified with 257 participants receiving placebo and a low risk of bias per the Cochrane Collaboration Risk of Bias 2 (RoB2) tool. Participants receiving placebo on average had a measurable decline in muscle strength with a mean effect size of –0.398 (95% CI –0.652, –0.144) (P = 0.002). SMD changed by –0.009 (–0.016, –0.002) points per week (P = 0.015). Manual muscle testing was associated with higher heterogeneity (I2 = 67.68%) compared with quantitative muscle testing (I2 = 0%). Only three studies reported IBMFRS results. The pooled change in IBMFRS at 12 months was –2.189 points (–3.893, –0.485) on this 0 to 40-point scale (P = 0.012), with relatively high heterogeneity. Conclusion Participants with IBM displayed a measurable decline in their muscle strength and IBMFRS during clinical trials, in keeping with the disease’s slowly progressive nature. These estimates can inform sample size calculations in future studies.