Faculty Bibliography

OBJECTIVE:To examine factors associated with lag screw slide following fixation of intertrochanteric hip fractures with 1 type of cephalomedullary nail. METHODS:Retrospective review of patients operatively treated for intertrochanteric hip fractures (OTA/AO 31A1 and 31A2) with a single cephalomedullary nail (CMN) at a single academic medical centre between November 2014 and November 2023. CMN lag screw was placed in "dynamic" mode to allow for controlled collapse, or screw "slide." Screw slide was defined as the difference in lateral prominence of the lag screw at latest follow up compared to its initial position. Patients were grouped based on the amount of screw slide (<5 mm, 5-15 mm, >15 mm) and correlation analysis was performed. RESULTS: = 0.002) was associated with >15 mm screw slide. CONCLUSIONS:Excessive lag screw slide (>15 mm) was associated with higher patient BMI. Patients with higher BMIs should be monitored to identify excessive slide. Surgeons should attempt to keep the lag screw as close to the lateral cortex as possible. While the use of anti-osteoporotic therapy was associated with more slide, this was almost exclusively seen in patients only prescribed vitamin D and calcium.

Melanocyte stem cells (McSCs) are a crucial melanocyte reservoir within the hair follicle niche. This review provides an overview of the processes for McSC quiescence and activation. Because McSCs closely interact with hair follicle stem cells, we have focused on this interaction. Given the high prevalence of hair graying, the McSC system serves as a model for cellular aging. Here, we highlight current research on the mechanisms of hair graying.

BACKGROUND/UNASSIGNED:Dysregulated proteolysis is implicated in thoracic (thoracic aortic aneurysm [TAA]) and abdominal aortic aneurysm (AAA) pathogenesis, but proteolytic landscapes (degradomes) of aneurysmal and normal aorta and contributions of individual proteases remain undefined. Here, a proteome-wide approach was used to define and compare TAA and AAA degradomes and uncover the specific role in aortic remodeling of 2 proteases consistently identified in the aneurysms, CMA1 (mast cell chymase) and MMP9 (matrix metalloprotease 9). METHODS/UNASSIGNED:The mass spectrometry-based N-terminomics strategy, terminal amine isotopic labeling of substrates, was applied to Marfan syndrome TAAs (n=5), AAAs (n=16), and nondiseased thoracic aorta (n=4), and abdominal aorta (n=4) in a forward degradomics application, that is, to define substrate and protease degradomes. 8-plex iTRAQ terminal amine isotopic labeling of substrates was used for quantitative comparison of the tissue cohorts. Cleavage sites of CMA1 and MMP9 were sought by reverse degradomics, that is, digestion of aortic proteins with these proteases, followed by terminal amine isotopic labeling of substrates. CMA1 and MMP9 proteolysis of biglycan was further resolved using amino-terminal oriented mass spectrometry of substrates. RESULTS/UNASSIGNED:We experimentally annotated 20 885 proteolytically derived peptides and identified 129 proteases in the aortic tissues. Quantitative substrate degradome comparisons identified specific differentially modulated pathways and networks in TAAs and AAAs. Reverse degradomics elucidated >300 CMA1 and MMP9 substrate cleavage sites, of which many, including orthogonally validated biglycan cleavages, occurred in the disease degradomes. CONCLUSIONS/UNASSIGNED:Unbiased forward degradomics of the aortic wall from TAA, AAA, and nondiseased tissue provides a systems biology view of aortic wall breakdown and a new resource for its hitherto occult proteolytic landscape, demonstrating widespread extracellular matrix remodeling with disproportionate impact on proteoglycans. The findings provided insights into aortic aneurysm pathways and disease biomarkers and suggest involvement of numerous proteases. Mapping of specific proteolytic contributions of CMA1 and MMP9 illustrates a strategy for defining the activities of all proteases involved in aortic disease.

Brown adipose tissue is an evolutionary innovation in placental mammals that regulates body temperature through adaptive thermogenesis. Cold exposure activates brown adipose tissue thermogenesis through coordinated induction of brown adipogenesis, angiogenesis, and sympathetic innervation; however, how these processes are coordinated remains unclear. Here, we show that fragments of Slit guidance ligand 3 (SLIT3) drive crosstalk among adipocyte progenitors, endothelial cells, and sympathetic nerves. Adipocyte progenitors secrete SLIT3, which is cleaved into functionally distinct SLIT3-N and SLIT3-C fragments that independently promote angiogenesis and sympathetic innervation. We identify PLXNA1 as a receptor for SLIT3-C and demonstrate its essential role in sympathetic innervation of brown adipose tissue. Moreover, we identify BMP1 as the first SLIT protease described in vertebrates. Coordinated neurovascular expansion mediated by distinct SLIT3 fragments provides a bifurcated yet integrated mechanism that ensures a synchronized brown adipose tissue response to environmental challenges. Finally, this study reveals a previously unrecognized role for adipocyte progenitors in regulating tissue innervation.

The skin is the largest human organ and a site of substantial disease burden, yet its cellular and molecular organization across the body is largely undefined. Here we construct an organ-wide single-cell spatial atlas of ~1.2 million cells from normal adult human skin, resolving the location of 45 cell types across 114 samples encompassing 15 anatomic sites. We uncover site-specific stereotypic cell-type composition and their organization into ten multicellular neighborhoods, most notably a perivascular neighborhood reminiscent of skin-associated lymphoid tissue. Within this neighborhood, ligand-receptor (L-R) analyses identify a central role for tumor necrosis factor in maintaining CCL19⁺ perivascular fibroblasts, highlighting homeostatic immune-stromal crosstalk. Finally, comparing neighborhood dynamics in spatial transcriptomics of skin disease, we find pan-disease immune alterations in this perivascular neighborhood, suggesting spatial compartmentalization of pathogenic activity. Thus, multicellular neighborhoods underlie the skin's multiscale molecular to macroanatomic organization, orchestrate cell-cell interactions and anatomic site specialization and exhibit architectural disruption in disease.

The Drosophila corneal lens is an apical extracellular matrix structure with a biconvex shape that enables it to focus light onto the underlying photoreceptors. Here, we investigated how this shape is influenced by the source of one of its major components, the polysaccharide chitin. Knocking down the chitin synthase Krotzkopf verkehrt strongly reduced the thickness and curvature of the corneal lens. Conversely, enhancing chitin export by overexpressing Rebuf expanded and distorted the corneal lens. We found that the cone and primary pigment cells in the center of each ommatidium produce most of the chitin, and preventing chitin synthesis by these central cells reduced corneal lens curvature. Increasing chitin export from central cells increased the thickness of the central corneal lens, while increasing export from peripheral lattice cells made the edges thicker. The wild-type biconvex shape thus results from high levels of chitin production by central cells relative to peripheral cells, indicating that localized chitin secretion is critical for normal corneal lens curvature.

Epstein-Barr virus (EBV) plays a role in the pathogenesis of a wide variety of acute and chronic diseases. Cutaneous manifestations of EBV include exanthems, chronic infections, malignancies, and small vessel vasculitides. Clinically and histologically, many of these conditions can imitate each other, making diagnosis challenging. In this report, we present a case of a child who developed Gianotti-Crosti syndrome with histopathologic features of anti-neutrophil cytoplasmic antibody (ANCA) vasculitis in the setting of acute EBV infection. Furthermore, we review the literature on EBV-induced cutaneous small vessel vasculitis and discuss pathogenic mechanisms.

BACKGROUND & AIMS/UNASSIGNED:Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in patients with metabolic dysfunction-associated steatohepatitis (MASH). No therapy targets both diseases simultaneously, and a roadblock for discovering new treatments is the lack of animal models that recapitulate both diseases, especially in females. METHODS/UNASSIGNED:mice (n = 8-13) were fed a western diet (WD), modified choline-deficient high-fat diet (mCDHFD), or modified MASH-inducing diet (mMASHD) containing equivalent physiological levels of cholesterol. Comprehensive multiomics including metabolomics, lipidomics, and transcriptomics, alongside histopathological and biochemical analyses, were integrated to characterize concurrent MASH and atherosclerosis. Transcriptomics was validated in other mouse models and integrated with human data (n = 79). RESULTS/UNASSIGNED:0.04). Lipidomic analyses revealed dysregulated polyunsaturated fatty acid, steryl ester, and dihexosylceramide metabolism. Integration of mouse and human transcriptomes revealed similarities in metabolic and proinflammatory/proatherogenic pathways. CONCLUSION/UNASSIGNED:This sex-based multiomics analysis establishes a murine model of concurrent MASH and atherosclerosis, reveals sex-specific dietary responses, and identifies metabolic and transcriptional pathways with potential utility as biomarkers and therapeutic targets. IMPACT AND IMPLICATIONS/UNASSIGNED:mice, we found that different diets containing equivalent physiological levels of cholesterol induce sex-specific responses, with a modified choline-deficient high-fat diet effectively modeling both diseases in both sexes, while a western diet is effective only in males. Multiomics analyses identified key metabolic and inflammatory pathways linking MASH and atherosclerosis that mirror transcriptomic signatures found in humans, and highlight circulating cholesterol, CCL2, and sphinganine as potential biomarkers. These findings establish a translational model and reveal sex-specific metabolic pathways that will advance our understanding of the shared pathophysiology of MASH and atherosclerosis, and facilitate the development of dual therapeutic approaches, addressing an urgent unmet clinical need.

BACKGROUND:Pathogenic variants in plakophilin-2 (PKP2) cause arrhythmogenic cardiomyopathy (ACM) with intracellular calcium dysregulation as a major component of its arrhythmia phenotype. Recent adeno-associated viral (AAV) based Pkp2 (AAV-PKP2) gene therapy has shown promising results in a few different PKP2-associated ACM models. Fibroblast growth factor 21 (FGF21) has multiple cardioprotective effects and has recently emerged as a promising therapeutic agent for cardiovascular disease. OBJECTIVES/OBJECTIVE:To assess the efficacy and impact on calcium regulation of a novel AAV8-based FGF21 gene therapy on adult cardiac-specific, tamoxifen-activated PKP2 knockout (PKP2-cKO) mice. METHODS:Experiments were performed using a PKP2-cKO murine model. AAV8-FGF21 was delivered to adult mice by a single tail vein injection 7 days before tamoxifen-activated PKP2-cKO. Cardiac functions were monitored by echocardiography and electrocardiography. Intracellular calcium transients were investigated in acute isolated adult mouse cardiomyocytes and calcium fluorescent signals were acquired with the IonOptix system. RESULTS:Loss of PKP2 expression caused cardiac mechanical dysfunction and pro-arrhythmic phenotype in adult mouse models. AAV-mediated delivery of FGF21 mitigated the progression of biventricular structural changes, decreased the occurrence of adrenergic arrhythmias, and rescued intracellular calcium imbalance in the setting of PKP2 haploinsufficiency. In contrast, acute in vitro FGF21 treatment for 1 hour had no effect on intracellular calcium transients. CONCLUSIONS:These beneficial effects of AAV8-FGF21 on the PKP2-ACM phenotype suggest a therapeutic landscape for various targeted cardiomyopathies.