Faculty Bibliography

PURPOSE/OBJECTIVE:The purpose of this study was to quantify the regional histology of the long head of the biceps tendon (LHBT) and compare the histopathology present to clinical findings in patients with rotator cuff tears and SLAP lesions. METHODS:Prospectively enrolled patients undergoing an open subpectoral LHBT tenodesis in the setting of a rotator cuff (RTC) tear or SLAP lesion. Perioperative data were collected and the excised LHBT was analyzed by a fellowship trained pathologist. Tendons were sectioned into proximal (biceps anchor), middle (bicipital groove), and distal (myotendinous junction) portions. Sections were stained with Movat's pentachrome stain and digitized for analysis. Comparisons were made between the histologic findings present in the setting of a rotator cuff tear with those seen in the setting of a SLAP tear. RESULTS:39 tendons were analyzed: 20 from patients with SLAP lesions (mean age of 44.7 years, range 23-60 years) and 19 from patients with rotator cuff tears (mean age of 58.7 years, range 43-71). Patients with the most pathologic tendons in the bicipital groove were significantly older (59.4 vs. 50.4 years; p < 0.05), reported higher pre-operative VAS scores (6.6 vs. 5.0; p < 0.02), and demonstrated lower pre-operative ASES scores (41.6 vs. 50.7; p < 0.05). The RTC group showed significantly more mucinous degeneration at both the proximal (p < 0.03) and the middle (p < 0.01) tendon portions compared to the SLAP group. In both groups, the portions of proximal tendon showed significantly (p < 0.05) more mucinous degeneration than distal portions. CONCLUSION/CONCLUSIONS:Regional histologic differences exist in the LHBT. Rotator cuff patients showed the most degenerated tendon in the bicipital groove and these patients tended to be older and have higher VAS and lower ASES scores. Surgeons should consider performing a subpectoral biceps tenodesis as the bicipital groove portion of the tendon may be very degenerated, especially in patients with rotator cuff disease. Additional research is warranted to distinguish whether treating the biceps differently in distinct geographic regions affects patient outcomes. LEVEL OF EVIDENCE/METHODS:II.

In the version of this Article originally published, the surname of the author Edward A. Fisher was spelt incorrectly as 'Fischer'. This has now been corrected.

Membrane fission is a fundamental process in the regulation and remodelling of cell membranes. Dynamin, a large GTPase, mediates membrane fission by assembling around, constricting and cleaving the necks of budding vesicles¹. Here we report a 3.75 Å resolution cryo-electron microscopy structure of the membrane-associated helical polymer of human dynamin-1 in the GMPPCP-bound state. The structure defines the helical symmetry of the dynamin polymer and the positions of its oligomeric interfaces, which were validated by cell-based endocytosis assays. Compared to the lipid-free tetramer form², membrane-associated dynamin binds to the lipid bilayer with its pleckstrin homology domain (PHD) and self-assembles across the helical rungs via its guanine nucleotide-binding (GTPase) domain³. Notably, interaction with the membrane and helical assembly are accommodated by a severely bent bundle signalling element (BSE), which connects the GTPase domain to the rest of the protein. The BSE conformation is asymmetric across the inter-rung GTPase interface, and is unique compared to all known nucleotide-bound states of dynamin. The structure suggests that the BSE bends as a result of forces generated from the GTPase dimer interaction that are transferred across the stalk to the PHD and lipid membrane. Mutations that disrupted the BSE kink impaired endocytosis. We also report a 10.1 Å resolution cryo-electron microscopy map of a super-constricted dynamin polymer showing localized conformational changes at the BSE and GTPase domains, induced by GTP hydrolysis, that drive membrane constriction. Together, our results provide a structural basis for the mechanism of action of dynamin on the lipid membrane.

OBJECTIVES/OBJECTIVE:To investigate how muscle and fasciocutaneous flaps influence the progression of bone healing in acute Gustilo IIIB tibia fractures. DESIGN/METHODS:Retrospective Chart Review. SETTING/METHODS:Urban Academic Level I Trauma Center. PATIENTS/PARTICIPANTS/METHODS:Between 2006 and 2016, 39 patients from a database of operatively treated long bone fractures met the inclusion criteria, which consisted of adults with acute Gustilo IIIB tibia shaft fracture requiring flap coverage and having at least 6 months of radiographic follow-up. INTERVENTION/METHODS:Soft tissue coverage for patients with Gustilo IIIB open tibia fractures was performed with either a muscle flap or fasciocutaneous flap. MAIN OUTCOME MEASUREMENTS/METHODS:A radiographic union score for tibia (RUST) fractures, used to evaluate fracture healing, was assigned to patients' radiographs postoperatively, at 3, 6, and 12 months from the initial fracture date. Mean RUST scores at these time points were compared between those of patients with muscle flaps and fasciocutaneous flaps. Union was defined as a RUST score of 10 or higher. RESULTS:There was a significant difference (P = 0.026) in the mean RUST score at 6 months between the muscle group (8.54 ± 1.81) and the fasciocutaneous group (6.92 ± 2.46). There was no significant difference in the mean RUST score at 3 months (P = 0.056) and at 12 months (P = 0.947) between the 2 groups. There was also significance in the number of fractures reaching union, favoring muscle flaps, at 6 months (P = 0.020). CONCLUSIONS:Patients with acute Gustilo IIIB tibia fractures who received muscle flaps have significantly faster radiographic progression of bone healing in the first 6 months than do patients who received fasciocutaneous flaps. Furthermore, according to radiographic evaluation, more Gustilo IIIB tibia fractures receiving muscle flaps reach union by 6 months than those flapped with fasciocutaneous tissue. LEVEL OF EVIDENCE/METHODS:Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Fractures of the talus are challenging to manage, with historically poor outcomes and a high rate of complications. The rare nature of this injury limits the number of studies available to guide treatment. Fortunately, a number of advancements have been made in the last decade. There is increased recognition regarding the importance of anatomic reconstruction of the osseous injury. Advanced imaging is used to assess the subtalar joint, where even slight displacement may predispose to arthritis. Increasing use of dual anteromedial and anterolateral approaches, along with plate fixation, has improved our ability to accurately restore the anatomy of the talus. Modification of the original Hawkins classification can both guide treatment and allow us to better predict which patients will develop avascular necrosis. Lastly, improved reconstructive techniques help address the most common complications after talus fracture, including arthritis, avascular necrosis, and malunion.

Barth syndrome (BTHS) is an X-linked genetic disorder resulting from mutations in the tafazzin gene (TAZ), which encodes the transacylase that remodels the mitochondrial phospholipid cardiolipin (CL). While most BTHS patients exhibit pronounced skeletal myopathy, the mechanisms linking defective CL remodeling and skeletal myopathy have not been determined. In this study, we constructed a CRISPR-generated stable tafazzin knockout (TAZ-KO) C2C12 myoblast cell line. TAZ-KO cells exhibit mitochondrial deficits consistent with other models of BTHS, including accumulation of monolyso-CL (MLCL), decreased mitochondrial respiratory, and increased mitochondrial ROS production. Additionally, tafazzin-deficiency was associated with impairment of myocyte differentiation. Future studies should determine whether alterations in myogenic determination contribute to the skeletal myopathy observed in BTHS patients. The BTHS myoblast model will enable studies to elucidate mechanisms by which defective CL remodeling interferes with normal myocyte differentiation and skeletal muscle ontogenesis.

OBJECTIVE:To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes. RESEARCH DESIGN AND METHODS:) 5.7-6.4% (39-46 mmol/mol). RESULTS:and FPG concentrations. CONCLUSIONS:D2d will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.

Insufficient or dysregulated energy metabolism may underlie diverse inherited and degenerative diseases, cancer, and even aging itself. ATP is the central energy carrier in cells, but critical pathways for regulating ATP levels are not systematically understood. We combined a pooled clustered regularly interspaced short palindromic repeats interference (CRISPRi) library enriched for mitochondrial genes, a fluorescent biosensor, and fluorescence-activated cell sorting (FACS) in a high-throughput genetic screen to assay ATP concentrations in live human cells. We identified genes not known to be involved in energy metabolism. Most mitochondrial ribosomal proteins are essential in maintaining ATP levels under respiratory conditions, and impaired respiration predicts poor growth. We also identified genes for which coenzyme Q10 (CoQ10) supplementation rescued ATP deficits caused by knockdown. These included CoQ10 biosynthetic genes associated with human disease and a subset of genes not linked to CoQ10 biosynthesis, indicating that increasing CoQ10 can preserve ATP in specific genetic contexts. This screening paradigm reveals mechanisms of metabolic control and genetic defects responsive to energy-based therapies.

BACKGROUND:What impact gene loss has on the evolution of developmental processes, and how function shuffling has affected retained genes driving essential biological processes, remain open questions in the fields of genome evolution and EvoDevo. To investigate these problems, we have analyzed the evolution of the Wnt ligand repertoire in the chordate phylum as a case study. RESULTS:We conduct an exhaustive survey of Wnt genes in genomic databases, identifying 156 Wnt genes in 13 non-vertebrate chordates. This represents the most complete Wnt gene catalog of the chordate subphyla and has allowed us to resolve previous ambiguities about the orthology of many Wnt genes, including the identification of WntA for the first time in chordates. Moreover, we create the first complete expression atlas for the Wnt family during amphioxus development, providing a useful resource to investigate the evolution of Wnt expression throughout the radiation of chordates. CONCLUSIONS:Our data underscore extraordinary genomic stasis in cephalochordates, which contrasts with the liberal and dynamic evolutionary patterns of gene loss and duplication in urochordate genomes. Our analysis has allowed us to infer ancestral Wnt functions shared among all chordates, several cases of function shuffling among Wnt paralogs, as well as unique expression domains for Wnt genes that likely reflect functional innovations in each chordate lineage. Finally, we propose a potential relationship between the evolution of WntA and the evolution of the mouth in chordates.

Thermogenic fat expends energy during cold for temperature homeostasis, and its activity regulates nutrient metabolism and insulin sensitivity. We measured cold-activated lipid landscapes in circulation and in adipose tissue by MS/MS^ALL shotgun lipidomics. We created an interactive online viewer to visualize the changes of specific lipid species in response to cold. In adipose tissue, among the approximately 1,600 lipid species profiled, we identified the biosynthetic pathway of the mitochondrial phospholipid cardiolipin as coordinately activated in brown and beige fat by cold in wild-type and transgenic mice with enhanced browning of white fat. Together, these data provide a comprehensive lipid bio-signature of thermogenic fat activation in circulation and tissue and suggest pathways regulated by cold exposure.