Hair Cell Mechanotransduction Regulates Spontaneous Activity and Spiral Ganglion Subtype Specification in the Auditory System.

Type I spiral ganglion neurons (SGNs) transmit sound information from cochlear hair cells to the CNS. Using transcriptome analysis of thousands of single neurons, we demonstrate that murine type I SGNs consist of subclasses that are defined by the expression of subsets of transcription factors, cell adhesion molecules, ion channels, and neurotransmitter receptors. Subtype specification is initiated prior to the onset of hearing during the time period when auditory circuits mature. Gene mutations linked to deafness that disrupt hair cell mechanotransduction or glutamatergic signaling perturb the firing behavior of SGNs prior to hearing onset and disrupt SGN subtype specification. We thus conclude that an intact hair cell mechanotransduction machinery is critical during the pre-hearing period to regulate the firing behavior of SGNs and their segregation into subtypes. Because deafness is frequently caused by defects in hair cells, our findings have significant ramifications for the etiology of hearing loss and its treatment.

E3 ubiquitin ligase ZBTB25 suppresses beta coronavirus infection through ubiquitination of the main viral protease MPro.

The main protease of severe acute respiratory syndrome coronavirus 2, Mpro, is a key viral protein essential for viral infection and replication. Mpro has been the target of many pharmacological efforts; however, the host-specific regulation of Mpro protein remains unclear. Here, we report the ubiquitin-proteasome-dependent degradation of Mpro protein in human cells, facilitated by the human E3 ubiquitin ligase ZBTB25. We demonstrate that Mpro has a short half-life that is prolonged via proteasomal inhibition, with its Lys-100 residue serving as a potential ubiquitin acceptor. Using in vitro binding assays, we observed ZBTB25 and Mpro bind to each other in vitro, and using progressive deletional mapping, we further uncovered the required domains for this interaction. Finally, we used an orthologous beta-coronavirus infection model and observed that genetic ablation of ZBTB25 resulted in a more highly infective virus, an effect lost upon reconstitution of ZBTB25 to deleted cells. In conclusion, these data suggest a new mechanism of Mpro protein regulation as well as identify ZBTB25 as an anticoronaviral E3 ubiquitin ligase.

Functional and clinical studies reveal pathophysiological complexity of CLCN4-related neurodevelopmental condition.

Missense and truncating variants in the X-chromosome-linked CLCN4 gene, resulting in reduced or complete loss-of-function (LOF) of the encoded chloride/proton exchanger ClC-4, were recently demonstrated to cause a neurocognitive phenotype in both males and females. Through international clinical matchmaking and interrogation of public variant databases we assembled a database of 90 rare CLCN4 missense variants in 90 families: 41 unique and 18 recurrent variants in 49 families. For 43 families, including 22 males and 33 females, we collated detailed clinical and segregation data. To confirm causality of variants and to obtain insight into disease mechanisms, we investigated the effect on electrophysiological properties of 59 of the variants in Xenopus oocytes using extended voltage and pH ranges. Detailed analyses revealed new pathophysiological mechanisms: 25% (15/59) of variants demonstrated LOF, characterized by a "shift" of the voltage-dependent activation to more positive voltages, and nine variants resulted in a toxic gain-of-function, associated with a disrupted gate allowing inward transport at negative voltages. Functional results were not always in line with in silico pathogenicity scores, highlighting the complexity of pathogenicity assessment for accurate genetic counselling. The complex neurocognitive and psychiatric manifestations of this condition, and hitherto under-recognized impacts on growth, gastrointestinal function, and motor control are discussed. Including published cases, we summarize features in 122 individuals from 67 families with CLCN4-related neurodevelopmental condition and suggest future research directions with the aim of improving the integrated care for individuals with this diagnosis.

Retinal vascular remodeling in photoreceptor degenerative disease.

Abnormal vasculature in the retina, specifically tortuous vessels and capillary degeneration, is common in many of the most prevalent retinal degenerative diseases, currently affecting millions of people across the world. However, the formation and development of abnormal vasculature in the context of retinal degenerative diseases are still poorly understood. The FVB/N (rd1) and rd10 mice are well-studied animal models of retinal degenerative diseases, but how photoreceptor degeneration leads to vascular abnormality in the diseases remains to be elucidated. Here, we used advancements in confocal microscopy, immunohistochemistry, and image analysis software to systematically characterize the pathological vasculature in the FVB/N (rd1) and rd10 mice, known as a chronic, rapid and slower retinal degenerative model, respectively. We demonstrated that there was plexus-specific vascular degeneration in the retinal trilaminar vascular network paralleled to photoreceptor degeneration in the diseased retinas. We also quantitatively analyzed the vascular structural architecture in the wild-type and diseased retinas to provide valuable information on vascular remodeling in retinal degenerative disease.

A Fbxo48 inhibitor prevents pAMPKα degradation and ameliorates insulin resistance.

The adenosine monophosphate (AMP)-activated protein kinase (Ampk) is a central regulator of metabolic pathways, and increasing Ampk activity has been considered to be an attractive therapeutic target. Here, we have identified an orphan ubiquitin E3 ligase subunit protein, Fbxo48, that targets the active, phosphorylated Ampkα (pAmpkα) for polyubiquitylation and proteasomal degradation. We have generated a novel Fbxo48 inhibitory compound, BC1618, whose potency in stimulating Ampk-dependent signaling greatly exceeds 5-aminoimidazole-4-carboxamide-1-ß-ribofuranoside (AICAR) or metformin. This compound increases the biological activity of Ampk not by stimulating the activation of Ampk, but rather by preventing activated pAmpkα from Fbxo48-mediated degradation. We demonstrate that, consistent with augmenting Ampk activity, BC1618 promotes mitochondrial fission, facilitates autophagy and improves hepatic insulin sensitivity in high-fat-diet-induced obese mice. Hence, we provide a unique bioactive compound that inhibits pAmpkα disposal. Together, these results define a new pathway regulating Ampk biological activity and demonstrate the potential utility of modulating this pathway for therapeutic benefit.

FAF1 Gene Involvement in Pituitary Corticotroph Tumors.

Cushing's disease (CD) is caused by rare pituitary corticotroph tumors that lead to corticotropin (ACTH) excess. Variants in FAF1, a pro-apoptotic protein involved in FAS-induced cell death, have been implicated in malignant disorders but the involvement of FAF1 in pituitary tumors has not been studied. Genetic data from patients with CD were reviewed for variants in FAF1 gene. Knockout mice (KO) were followed to assess the development of any pituitary disorder or cortisol excess. AtT-20 cells were used to study the effects of the variants of interest on ACTH secretion and cell proliferation. Three variants of interest were identified in 5 unique patients, two of which had rare allele frequency in genomic databases and were predicted to be likely pathogenic. KO mice were followed over time and no difference in their length/weight was noted. Additionally, KO mice did not develop any pituitary lesions and retained similar corticosterone secretion with wild type. AtT-20 cells transfected with FAF1 variants of interest or WT expression plasmids showed no significant difference in cell death or Pomc gene expression. However, in silico prediction models suggested significant differences in secondary structures of the produced proteins. In conclusion, we identified two FAF1 variants in patients diagnosed with CD with a potential pathogenic effect on the protein function and structure. Our in vitro and in vivo studies did not reveal an association of FAF1 defects with pituitary tumorigenesis and further studies may be needed to understand any association.

Current status of the assessment of sarcopenia, frailty, physical performance and functional status in chronic kidney disease patients.

PURPOSE OF REVIEW: Low physical function, frailty, and sarcopenia are common complications of chronic kidney disease (CKD). In this article, we review the epidemiology and pathogenesis of low physical function, as well as its associations with adverse outcomes in CKD patients. Additionally, we present various traditional and novel methods for assessment of physical function in CKD patients. RECENT FINDINGS: In nondialysis dependent (NDD) and dialysis-dependent CKD patients, the prevalence of low physical function, frailty, and sarcopenia are substantially higher than in the general population. The potential mechanisms of low physical function, frailty, and sarcopenia in CKD patients are due to various factors including underlying kidney disease, co-existing comorbidities, and certain therapeutic interventions utilized in CKD. Increasing evidence has also uncovered the ill effects of impaired physical function on clinical outcomes in CKD patients. SUMMARY: Routine assessment of physical function is an under-utilized yet important component in the management of CKD patients. Future studies are needed to determine how prescription of exercise and increased daily physical activity can be tailored to optimize the health and well-being of NDD and dialysis-dependent CKD patients in pursuit of successful aging.

Pin-Related Complications in Computer Navigated and Robotic-Assisted Knee Arthroplasty: A Systematic Review.

BACKGROUND: Computer-assisted navigation (CAN) and robotic-assisted (RA) knee arthroplasty procedures carry unique risks of tracking pin-related complications. This systematic review aimed to quantitatively assess the incidence, timing, treatment, and clinical outcomes of all tracking pin-related complications following CAN and RA knee arthroplasty. METHODS: A systematic review was performed using PubMed, Cochrane Central and Scopus databases. All clinical studies that documented pin-related complications associated with the use of CAN or RA for total or partial knee arthroplasty were included. Descriptive statistics were analyzed when data were available. RESULTS: Thirty-six studies were included: 18 case reports (25 cases) and 18 randomized controlled trials, cohort studies and case series i.e., non-case reports (7,336 cases). The most common pin-related complication among case reports was fracture (n = 22; 81%). The overall rate of pin-related complications among non-case reports was 1.4%. The intraoperative and postoperative complication with the highest incidence were pin dislodgement (0.6%) and superficial pin site infections (0.6%), respectively. Most postoperative complications were related to the tibial site (69%). All complications were effectively treated and resolved at follow-up. CONCLUSION: Pin-related complications following CAN and RA knee arthroplasty are relatively uncommon. While pin loosening, superficial infections and fractures have been most commonly documented, other complications such as vascular injury, myositis ossificans, and osteomyelitis can also occur. The potential for pin-related complications should be considered by arthroplasty surgeons, especially during early stages of adoption. Further studies investigating patient risk factors for pin-related complications are warranted.

Idiopathic granulomatous mastitis: case series and clinical review.

Idiopathic granulomatous mastitis is a chronic inflammatory breast disorder that typically affects young, parous women, often following lactation. Patients present with tender, erythematous breast lesions with histological evidence of non-caseating granulomata and an inflammatory cell infiltrate. An immune-mediated pathophysiology is hypothesised and an association with lipophilic Corynebacterium species is observed. Initial diagnosis is often delayed due to lack of awareness of the condition and management of refractory disease can be challenging. We present an extensive case series of patients collaboratively managed by subspecialty physicians and surgeons at a single centre in Sydney, Australia. The accompanying review expands on features of this condition and supports the utility of a multidisciplinary approach.

Retinoic acid receptor regulation of epimorphic and homeostatic regeneration in the axolotl.

Salamanders are capable of regenerating amputated limbs by generating a mass of lineage-restricted cells called a blastema. Blastemas only generate structures distal to their origin unless treated with retinoic acid (RA), which results in proximodistal (PD) limb duplications. Little is known about the transcriptional network that regulates PD duplication. In this study, we target specific retinoic acid receptors (RARs) to either PD duplicate (RA treatment or RARγ agonist) or truncate (RARß antagonist) regenerating limbs. RARE-EGFP reporter axolotls showed divergent reporter activity in limbs undergoing PD duplication versus truncation, suggesting differences in patterning and skeletal regeneration. Transcriptomics identified expression patterns that explain PD duplication, including upregulation of proximal homeobox gene expression and silencing of distal-associated genes, whereas limb truncation was associated with disrupted skeletal differentiation. RARß antagonism in uninjured limbs induced a loss of skeletal integrity leading to long bone regression and loss of skeletal turnover. Overall, mechanisms were identified that regulate the multifaceted roles of RARs in the salamander limb including regulation of skeletal patterning during epimorphic regeneration, skeletal tissue differentiation during regeneration, and homeostatic regeneration of intact limbs.

Identifying co-morbid fibromyalgia in patients with systemic lupus erythematosus using the Multi-Dimensional Health Assessment Questionnaire.

OBJECTIVE: Fibromyalgia (FM) is prevalent but often under-recognized in patients with systemic lupus erythematosus (SLE). Patient-reported outcomes (PROs) from the Multi-Dimensional Health Assessment Questionnaire (MDHAQ) can identify co-morbid FM in patients with rheumatic diseases. The present study examined the utility of the MDHAQ in recognizing FM in patients with SLE during routine consultations. METHODS: Patients with SLE completed an MDHAQ. FM status was determined by the validated 2016 revision of the ACR 2010/2011 preliminary FM criteria. Individual PROs from the MDHAQ and composite Fibromyalgia Assessment Tool (FAST) indices of the discriminatory PROs were compared between patients with and without FM using Student's unpaired t-test and receiver operating characteristic curve analysis to determine the area under the curve (AUC). The physician's clinical impression of FM was recorded, and the SLE Disease Activity Index was used to assess disease activity. RESULTS: Of 88 patients with SLE, 23 (26%) satisfied the 2016 FM criteria. The FAST3 composite measure of two out of three of pain (≥6/10), joint count (≥16/48) and symptom checklist (≥16/60) correctly classified 89% of patients (AUC=0.90, kappa=0.71). Physician diagnosis demonstrated moderate agreement with the 2016 FM criteria (kappa=0.43) but missed 43% of patients with FM. In the presence of active disease, the FAST3 correctly classified 91% of patients. CONCLUSIONS: Co-morbid FM is prevalent in SLE yet often underdiagnosed by physicians. The simple FAST3 index of the MDHAQ provides an easy-to-use self-reported tool to improve identification of FM in patients with SLE.

Validation of anti-glucocerebrosidase antibodies for western blot analysis on protein lysates of murine and human cells.

Gaucher disease (GD) is a rare lysosomal storage disorder caused by mutations in the GBA1 gene, encoding the lysosome-resident glucocerebrosidase enzyme involved in the hydrolysis of glucosylceramide. The discovery of an association between mutations in GBA1 and the development of synucleinopathies, including Parkinson disease, has directed attention to glucocerebrosidase as a potential therapeutic target for different synucleinopathies. These findings initiated an exponential growth in research and publications regarding the glucocerebrosidase enzyme. The use of various commercial and custom-made glucocerebrosidase antibodies has been reported, but standardized in-depth validation is still not available for many of these antibodies. This work details the evaluation of several previously reported glucocerebrosidase antibodies for western blot analysis, tested on protein lysates of murine gba+/+ and gba-/- immortalized neurons and primary human wild-type and type 2 GD fibroblasts.

Red cell distribution width correlates with fatigue levels in a diverse group of patients with systemic lupus erythematosus irrespective of anaemia status.

OBJECTIVES: Fatigue remains a debilitating feature of systemic lupus erythematosus (SLE). Although in some cases this may be the result of intercurrent fibromyalgia, mood disorder or untreated metabolic syndrome, in many cases the cause is unclear. The aim of this study was to investigate the relationship between fatigue and red cell distribution width (RDW), a measure of variability in erythrocyte size and volume. METHODS: A total of 225 patients were recruited from three clinics in England and Australia. Patients completed the Functional Assessment of Chronic Illness Therapy (FACIT) Fatigue Score or 12-item Short Form survey (SF-12) to measure fatigue, which was compared with RDW and haemoglobin. In a subgroup of 72 patients, markers of disease activity were also assessed for correlation with fatigue using univariate and multivariate analysis with fatigue as the dependent variable. RESULTS: In all three groups, significant correlations between fatigue and RDW were observed (p<0.001; p=0.02; p<0.001 respectively) and this was preserved in multivariate analysis. There was no correlation between fatigue and haemoglobin in two groups (with the correlation between RDW and fatigue remaining significant in non-anaemic patients in the third group). In subgroup analysis, fatigue was not associated with any measures of disease activity. CONCLUSIONS: We report a reproducible, statistically significant association between RDW and fatigue levels in a diverse population of patients with SLE. The findings of this study raise the possibility of a potential novel biological basis for fatigue in those in whom there is a lack of an alternate explanation.

Flavopiridol enhances ABT-199 sensitivity in unfavourable-risk multiple myeloma cells in vitro and in vivo.

BACKGROUND: The BCL-2-specific BH3-mimetic ABT-199 (venetoclax) has been reported to be principally active against favourable-risk multiple myeloma (MM) cells, prompting efforts to extend its activity to include more resistant, higher-risk MM subsets. METHODS: Effects of the CDK9 inhibitor flavopiridol (FP; alvocidib) on responses to ABT-199 were examined in MM cells. Cell death and protein expression were evaluated by western blot and immunofluorescence. Xenograft models were used to study combination effects in vivo. RESULTS: FP synergistically increased ABT-199 lethality in both ABT-199-sensitive and insensitive MM cells. FP blocked CDK9 activation/positive transcription elongation factor B phosphorylation, downregulated MCL-1, increased BCL-2/MCL-1 ratios, and upregulated BIM. MCL-1 ectopic expression or knockdown in MM cells significantly diminished or increased ABT-199 sensitivity, respectively. CDK9 knockdown triggered MCL-1 downregulation and increased ABT-199 activity, whereas BIM knockdown significantly reduced FP/ABT-199 lethality. FP also enhanced ABT-199 lethality in unfavourable prognosis primary MM cells. HS-5 cell co-culture failed to protect MM cells from the FP/ABT-199 regimen, suggesting circumvention of microenvironmental signals. Finally, FP/ABT-199 significantly increased survival in systemic xenograft and immune-competent MM models while exhibiting minimal toxicity. CONCLUSIONS: These findings argue that CDK9 inhibitors, for example, FP may increase the antimyeloma activity of ABT-199, including in unfavourable-risk MM minimally responsive to ABT-199 alone.

A case report of autoimmune necrotizing myositis presenting as dysphagia and neck swelling.

BACKGROUND: Severe dysphagia may occur in the immune mediated necrotizing myopathies (IMNM). Neck swelling and severe dysphagia as the initial symptoms upon presentation has not been previously described. CASE PRESENTATION: A 55-year-old male with a 4 week history of neck swelling, fatigue, dysphagia, myalgias, night sweats, and cough was admitted for an elevated CK. He underwent extensive infectious and inflammatory evaluation including neck imaging and muscle biopsy. Neck CT and MRI showed inflammation throughout his strap muscles, retropharyngeal soft tissues and deltoids. Infectious work up was negative. Deltoid muscle biopsy demonstrated evidence of IMNM. Lab tests revealed anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies confirming the diagnosis of HMGCR IMNM. CONCLUSIONS: HMGCR IMNM is a rare and incompletely understood disease process. Awareness of HMGCR IMNM could potentially lead to earlier diagnosis, treatment and improved clinical outcomes as disease progression can be rapid and severe.

Screening for Skin Cancer in Adults: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force.

IMPORTANCE: Skin cancer, primarily melanoma, is a leading cause of morbidity and mortality in the United States. OBJECTIVE: To provide an updated systematic review for the US Preventive Services Task Force regarding clinical skin cancer screening among adults. DATA SOURCES: MEDLINE, PubMed, and the Cochrane Central Register of Controlled Trials were searched for relevant studies published from January 1, 1995, through June 1, 2015, with surveillance through February 16, 2016. STUDY SELECTION: English-language studies conducted in asymptomatic populations 15 years and older at general risk for skin cancer. DATA EXTRACTION AND SYNTHESIS: Relevant data were abstracted, and study quality was rated. MAIN OUTCOMES AND MEASURES: Melanoma incidence and mortality, harms from cancer screening, diagnostic accuracy, and stage distribution. RESULTS: No randomized clinical trials were identified. There was limited evidence on the association between skin cancer screening and mortality. A German ecologic study (n = 360,288) found a decrease of 0.8 per 100,000 melanoma deaths in a region with population-based skin cancer screening compared with no change or slight increases in comparison regions. The number of excisions needed to detect 1 skin cancer from clinical visual skin examinations varied by age and sex; for example, 22 for women 65 years or older compared with 41 for women aged 20 to 34 years. In 2 studies of performing visual skin examination, sensitivity to detect melanoma was 40.2% and specificity was 86.1% when conducted by primary care physicians (n = 16,383). Sensitivity was 49.0% and specificity was 97.6% when skin examinations were performed by dermatologists (n = 7436). In a case-control study of melanoma (n = 7586), cases diagnosed with thicker lesions (>0.75 mm) had an odds ratio of 0.86 (95% CI, 0.75-0.98) for receipt of a physician skin examination in the prior 3 years compared with controls. Eight cohort studies (n = 236,485) demonstrated a statistically significant relationship between the degree of disease involvement at diagnosis and melanoma mortality, regardless of the characterization of the stage or lesion thickness. Tumor thickness greater than 4.0 mm was associated with increased melanoma mortality compared with thinner lesions, and late stage at diagnosis was associated with increased all-cause mortality. CONCLUSIONS AND RELEVANCE: Only limited evidence was identified for skin cancer screening, particularly regarding potential benefit of skin cancer screening on melanoma mortality. Future research on skin cancer screening should focus on evaluating the effectiveness of targeted screening in those considered to be at higher risk for skin cancer.

Perceptions of basic, advanced, and pediatric life support training in a United States medical school.

BACKGROUND: Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), and Pediatric Advanced Life Support (PALS) are integral parts of emergency resuscitative care. Although this training is usually reserved for residents, introducing the training in the medical student curriculum may enhance acquisition and retention of these skills. OBJECTIVES: We developed a survey to characterize the perceptions and needs of graduating medical students regarding BLS, ACLS, and PALS training. METHODS: This was a study of graduating 4th-year medical students at a U.S. medical school. The students were surveyed prior to participating in an ACLS course in March of their final year. RESULTS: Of 152 students, 109 (71.7%) completed the survey; 48.6% of students entered medical school without any prior training and 47.7% started clinics without training; 83.4% of students reported witnessing an average of 3.0 in-hospital cardiac arrests during training (range of 0-20). Overall, students rated their preparedness 2.0 (SD 1.0) for adult resuscitations and 1.7 (SD 0.9) for pediatric resuscitations on a 1-5 Likert scale, with 1 being unprepared. A total of 36.8% of students avoided participating in resuscitations due to lack of training; 98.2%, 91.7%, and 64.2% of students believe that BLS, ACLS, and PALS, respectively, should be included in the medical student curriculum. CONCLUSIONS: As per previous studies that have examined this topic, students feel unprepared to respond to cardiac arrests and resuscitations. They feel that training is needed in their curriculum and would possibly enhance perceived comfort levels and willingness to participate in resuscitations.

Predicting Tracheostomy Need on Admission to the Intensive Care Unit-A Multicenter Machine Learning Analysis.

OBJECTIVE: It is difficult to predict which mechanically ventilated patients will ultimately require a tracheostomy which further predisposes them to unnecessary spontaneous breathing trials, additional time on the ventilator, increased costs, and further ventilation-related complications such as subglottic stenosis. In this study, we aimed to develop a machine learning tool to predict which patients need a tracheostomy at the onset of admission to the intensive care unit (ICU). STUDY DESIGN: Retrospective Cohort Study. SETTING: Multicenter Study of 335 Intensive Care Units between 2014 and 2015. METHODS: The eICU Collaborative Research Database (eICU-CRD) was utilized to obtain the patient cohort. Inclusion criteria included: (1) Age >18 years and (2) ICU admission requiring mechanical ventilation. The primary outcome of interest included tracheostomy assessed via a binary classification model. Models included logistic regression (LR), random forest (RF), and Extreme Gradient Boosting (XGBoost). RESULTS: Of 38,508 invasively mechanically ventilated patients, 1605 patients underwent a tracheostomy. The XGBoost, RF, and LR models had fair performances at an AUROC 0.794, 0.780, and 0.775 respectively. Limiting the XGBoost model to 20 features out of 331, a minimal reduction in performance was observed with an AUROC of 0.778. Using Shapley Additive Explanations, the top features were an admission diagnosis of pneumonia or sepsis and comorbidity of chronic respiratory failure. CONCLUSIONS: Our machine learning model accurately predicts the probability that a patient will eventually require a tracheostomy upon ICU admission, and upon prospective validation, we have the potential to institute earlier interventions and reduce the complications of prolonged ventilation.

Impact of Human Recombinant Irisin on Tissue-Engineered Skeletal Muscle Structure and Function.

Tissue engineering of exogenous skeletal muscle units (SMUs) through isolation of muscle satellite cells from muscle biopsies is a potential treatment method for acute volumetric muscle loss (VML). A current issue with this treatment process is the limited capacity for muscle stem cell (satellite cell) expansion in cell culture, resulting in a decreased ability to obtain enough cells to fabricate SMUs of appropriate size and structural quality and that produce native levels of contractile force. This study determined the impact of human recombinant irisin on the growth and development of three-dimensional (3D) engineered skeletal muscle. Muscle satellite cells were cultured without irisin (control) or with 50, 100, or 250 ng/mL of irisin supplementation. Light microscopy was used to analyze myotube formation with particular focus placed on the diameter and density of the monotubes during growth of the 3D SMU. Following the formation of 3D constructs, SMUs underwent measurement of maximum tetanic force to analyze contractile function, as well as immunohistochemical staining, to characterize muscle structure. The results indicate that irisin supplementation with 250 ng/mL significantly increased the average diameter of myotubes and increased the proliferation and differentiation of myoblasts in culture but did not have a consistent significant impact on force production. In conclusion, supplementation with 250 ng/mL of human recombinant irisin promotes the proliferation and differentiation of myotubes and has the potential for impacting contractile force production in scaffold-free tissue-engineered skeletal muscle.