Faculty Bibliography

Determining the clinical relevance of BRCA2 variants of uncertain significance is critical for informed risk management. Recently, two saturation genome editing studies assessed the functional effects of all single nucleotide variants in the BRCA2 C-terminal DNA Binding Domain. To improve the accuracy of functional data used for ACMG/AMP variant classification, we combined results from these studies in four composite models and evaluated the performance of each model using variants with known classifications. Here, we show that an "Integrated VarCall Model", which combined raw functional data for 6383 variants from the original studies, yielded 98.8% accuracy and out-performed the original studies and other combined data models. Incorporation of the "Integrated VarCall Model" functional data with other sources of evidence according to ClinGen BRCA1/2 variant curation expert panel specifications resulted in classification of 5926 (92.8%) BRCA2 variants as pathogenic (n = 735) or benign (n = 5191) and provides valuable insights for individuals with BRCA2 variants.

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.

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.

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 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.

PURPOSE/OBJECTIVE:To dissect the clinical and immunological features of people living with HIV (PLWH) diagnosed with melanoma, who have consistently shown worse outcomes than HIV-negative individuals (PLw/oH) with the same cancer. EXPERIMENTAL DESIGN/METHODS:We analyzed electronic health records from 1,087 PLWH and 394,437 PLw/oH with melanoma. Demographic and clinical characteristics were compared. Spatial immune transcriptomics (72 immune-related genes) was performed on melanoma tumor samples (n=11), with downstream validation using multiplex immunofluorescence (n=15 PLWH, n=14 PLw/oH). RESULTS:PLWH were diagnosed at a younger age, had greater representation of Hispanic and Black individuals, and showed reduced survival. They also had a markedly increased risk of brain metastases. PLWH experienced significant delays in initiating immune checkpoint inhibitor (ICI) therapy and had worse post-ICI survival, even after balancing covariates. Spatial transcriptomics revealed a more immunosuppressive tumor microenvironment in PLWH, with increased transcription of immune checkpoints (PD1, LAG3) and reduced antigen-presentation markers (HLA-DRB, B2M), with distinct spatial distributions in tumors and surrounding microenvironments. Multiplex immunofluorescence demonstrated features of an exhausted CD8⁺ T cell compartment, including enrichment of PD1intLAG3⁻ and PD1intLAG3⁺ subpopulations, and a significant accumulation of myeloid-derived suppressor cells (CD11b⁺ HLA-DR⁻ CD33⁺). CONCLUSIONS:Melanoma in PLWH is associated with distinct clinical and immunological features, including delayed ICI treatment, reduced survival, and an immunosuppressive microenvironment with exhausted CD8⁺ T cells and expanded myeloid-derived suppressor cells. These findings suggest that chronic HIV infection may impair antitumor immunity in melanoma. Targeting the pathways identified here may improve therapeutic responses and outcomes in this population.

Membrane transport proteins translocate diverse cargos, ranging from small sugars to entire proteins, across cellular membranes^1-3. A few structurally distinct protein families have been described that account for most of the known membrane transport processes^4-6. However, many membrane proteins with predicted transporter functions remain uncharacterized. Here we determined the structure of Escherichia coli LetAB, a phospholipid transporter involved in outer membrane integrity, and found that LetA adopts a distinct architecture that is structurally and evolutionarily unrelated to known transporter families. LetA localizes to the inner membrane, where it is poised to load lipids into its binding partner, LetB, a mammalian cell entry (MCE) protein that forms an approximately 225 Å long tunnel for lipid transport across the cell envelope. Unexpectedly, the LetA transmembrane domains adopt a fold that is evolutionarily related to the eukaryotic tetraspanin family of membrane proteins, including transmembrane AMPA receptor regulatory proteins (TARPs) and claudins. Through a combination of deep mutational scanning, molecular dynamics simulations, AlphaFold-predicted alternative states and functional studies, we present a model for how the LetA-like family of membrane transporters facilitates the transport of lipids across the bacterial cell envelope.