Faculty Bibliography

Expression of the IgE BCR is associated with increased B cell apoptosis, yet in persistent allergy, sustained production of IgE antibodies in the absence of allergen exposure suggests the existence of long-lived IgE plasma cells (PCs). Here we studied the development and localization of IgE PCs in mouse models of allergy. After immunization, IgE PCs underwent maturation in spleen and lymph nodes, acquiring a stable MHCII^loCD93⁺CD98^hiBCR^lo phenotype. Mature IgE PCs had a distinct transcriptional profile adapted to high protein synthesis, glycosylation, and survival and resisted BCR-crosslinking-induced apoptosis. Immunization induced a burst of short-lived IgE PC formation, followed by a reduced differentiation rate over time, compared with IgG1 PCs. Timestamping of PCs revealed long-lived IgE PCs that localize to the spleen, in addition to the bone marrow (BM). Thus, immune challenge can generate both short-lived and long-lived IgE PCs, with long-lived IgE PCs in spleen and BM contributing to allergy persistence.

BACKGROUND:Accumulated levels of mutant huntingtin protein (mHTT) and its fragments are considered contributors to the pathogenesis of Huntington's disease (HD). Stimulating autophagy may enhance clearance of mHTT and its aggregates which has been considered as a possible therapeutic strategy. However, the role and competence of the autophagy-lysosomal pathway (ALP) during HD progression in the human disease remains largely unknown. METHODS:Here, we used multiplex confocal and ultrastructural immunocytochemical analyses of ALP functional markers in relation to mHTT aggresome pathology in striatum and the less affected cortex or cerebellum of HD brains staged from Grade HD2 to HD4 by Vonsattel neuropathological criteria compared to controls. RESULTS:Immunolabeling revealed the localization of HTT/mHTT in ALP vesicular compartments labeled by autophagy-related adaptor proteins sequestosome 1 (p62/SQSTM1) and ubiquitin, and cathepsin D (CTSD) as well as HTT-positive inclusions. Although comparatively normal at HD2, neurons at later HD stages exhibited progressive enlargement and clustering of CTSD-immunoreactive autolysosomes/lysosomes and, ultrastructurally, autophagic vacuole/lipofuscin granules accumulated progressively, more prominently in striatum than cortex. These changes were accompanied by rises in levels of HTT/mHTT and p62/SQSTM1, particularly their fragments, in striatum but not in the cortex, and by increases of LAMP1 and LAMP2 RNA and LAMP1 protein. In addition, cargo-loaded autophagosomes and cathepsin-positive autolysosomes were readily observed, implying a lack of significant blockage in autophagosome formation and autophagosome-lysosome fusion. CONCLUSIONS:The findings collectively suggest that upregulated lysosomal biogenesis and preserved proteolysis maintain autophagic clearance in early-stage HD, but the observed progressive HTT build-up and AL accumulation at advanced disease stages may signify a failure in autophagy substrate clearance. These findings support the prospect that ALP stimulation applied at early disease stages, when clearance machinery is fully competent, could lead to therapeutic benefits in HD patients.

INTRODUCTION/BACKGROUND:The purpose of this study was to assess the effect of an acute traumatic meniscus tear that required repair in association with a tibial plateau fracture repair on outcomes. METHODS:Over a 17-year period, 843 patients presented with a tibial plateau fracture and were followed prospectively. 721 patients with Schatzker I-VI fractures were treated operatively via a standardized algorithm. 161 tibial plateau fractures (22.3 %) had an associated meniscus tear that underwent acute repair at the time of bony fixation. These patients were compared to operatively repaired tibial plateau fracture patients with no meniscus injury (NMR). Demographics were collected and outcomes including: radiographic healing, knee range of motion (ROM), and complication rates, were recorded. In addition, re-operation rates were compared and any reoperation for meniscus repair failure identified. All patients had a minimum of 1 year follow up. RESULTS:A total of 524 patients with a mean of 21.4 (range: 12-120) months follow up met inclusion criteria. Patients in the meniscus repair (MR) cohort had poorer knee extension (1.01 degrees, range: 0-30 degrees) compared to the NMR cohort (0.07 degrees, range: 0-10 degrees) (p < 0.001), in addition to poorer knee flexion (123 degrees, range: 0-145 degrees, p = 0.024). Additionally, MR patients reported higher pain scores (mean: 3 and range: 0-8, p = 0.005) at latest follow up. Finally, MR patients had higher rates of infection (8.1 % vs. 3.3 %, p = 0.025) and lateral collapse of the joint (p = 0.032). CONCLUSION/CONCLUSIONS:Patients who had a meniscus repair at the time of tibial plateau fracture repair were found to have poorer knee ROM, more patient reported pain at minimum 12 (mean 24) months post-operation. Additionally, these patients developed more post-operative complications than those patients who did not undergo a meniscus repair.

Astrocytic Ca²⁺ activity regulates activity-dependent synaptic plasticity, but its role in learning-related synaptic changes in the living brain remains unclear. We found that motor training induced synaptic potentiation on apical dendrites of layer 5 pyramidal neurons, as well as astrocytic Ca²⁺ rises in the mouse motor cortex. Reducing astrocytic Ca²⁺ led to synaptic depotentiation during motor training and subsequent impairment in performance improvement. Notably, synaptic depotentiation occurred on a fraction of dendrites with repetitive dendritic Ca²⁺ activity. On those dendrites, dendritic spines that were active before dendritic Ca²⁺ activity underwent CaMKII-dependent size reduction. In addition, the activation of adenosine receptors prevented repetitive dendritic Ca²⁺ activity and synaptic depotentiation caused by the reduction of astrocytic Ca²⁺, suggesting the involvement of ATP released from astrocytes and adenosine signaling in the processes. Together, these findings reveal the function of astrocytic Ca²⁺ in preventing synaptic depotentiation by limiting repetitive dendritic activity during learning.

Stress-induced dinucleoside tetraphosphates (Np₄Ns, where N is adenosine, guanosine, cytosine or uridine) are ubiquitous in living organisms, yet their function has been largely elusive for over 50 years. Recent studies have revealed that RNA polymerase can influence the cellular lifetime of transcripts by incorporating these alarmones into RNA as 5'-terminal caps. Here we present structural and biochemical data that reveal the molecular basis of noncanonical transcription initiation from Np₄As by Escherichia coli and Thermus thermophilus RNA polymerases. Our results show the influence of the first two nucleotide incorporation steps on capping efficiency and the different interactions of Np₄As with transcription initiation complexes. These data provide critical insights into the substrate selectivity that dictates levels of Np₄ capping in bacterial cells.

BACKGROUND:The knee's inflammatory response to ligamentous, meniscal, and cartilage injuries is complex and incompletely understood, particularly in the setting of concomitant injuries. Recent research has highlighted the potential utility of synovial fluid biomarker analysis in identifying factors involved in the progression of posttraumatic osteoarthritis. PURPOSE/OBJECTIVE:To investigate if unique patterns of knee injury are associated with distinct synovial fluid biomarker profiles at the time of surgical intervention. STUDY DESIGN/METHODS:Cross-sectional study; Level of evidence, 3. METHODS:Patients undergoing arthroscopic knee surgery were prospectively enrolled and asked to complete the Lysholm Knee Scoring Scale and visual analog scale for pain preoperatively. Synovial fluid was aspirated from the operative knee before surgical incision, and the concentrations of 10 biomarkers of interest were quantified. Patients with intraoperative evidence of articular cartilage, meniscal, and/or anterior cruciate ligament (ACL) injury were identified and included for subsequent analysis. Biomarker concentrations were log-normalized and standardized. Principal component analysis (PCA) was performed using biomarker variables to reduce dimensionality and extract key patterns. Multivariable linear regression for each retained principal component (PC) was performed with the predictors of age, sex, body mass index, symptom duration, ACL injury, meniscal injury, and Outerbridge grade. A separate regression analysis was performed to assess relationships between PCs and patient-reported outcomes controlling for the same variables. RESULTS:= .001; β = -.199). CONCLUSION/CONCLUSIONS:Cartilage lesions exhibited a synovial fluid inflammatory profile distinct from ACL and meniscal injury at the time of knee arthroscopy. While ACL and meniscal injuries displayed a pro-inflammatory phenotype, more severe cartilage lesions were associated with a reduced presence of anti-inflammatory markers. The pro-inflammatory phenotype also independently correlated with worse baseline knee function. These findings contribute to the understanding of the pathophysiology of ligamentous, meniscal, and cartilage injuries and may aid in the identification of pathology-specific treatments to help alter the natural history of disease.

In recent history, human life expectancy has increased significantly, resulting in a high burden of late-life morbidity and geriatric fractures. Changes to the body as a result of aging, such as degeneration of the bone marrow, osteoblast apoptosis, and a decline in hormone production, coupled with sarcopenia, are only a few factors that predispose the elderly to fractures. In addition, these factors further complicate surgical management, as they increase the risk of fixation failure, nonunion, malunion, and wound complications. As a result, the standards of geriatric fracture fixation must account for variables that are rarely included when planning for surgery in the younger population. Operative fixation should provide a stable limb to allow for early mobilization and weight bearing, lowering the risk of medical complications. Therefore, early mobility is of the utmost importance in the setting of most fragility fractures. However, early mobility in some, such as the pelvic fragility fracture, may lead to an increased risk for bleeding and death. Geriatric fractures carry significant morbidity, mortality, and financial risk, which indicates that there should be a continuing review and understanding of the multifactorial process leading toward and treatment strategies employed after geriatric fractures. The purpose of this review is to summarize the biology of aging, the causes, effects, and treatments of sarcopenia, the current fixation strategies of geriatric fractures, and the importance of mobility in the geriatric patient.

Insulin resistance impairs benefits of lipid-lowering treatment as evidenced by higher cardiovascular risk in individuals with type 2 diabetes versus those without. Because platelet activity is higher in insulin-resistant patients and promotes atherosclerosis progression, we questioned whether platelets impair inflammation resolution in plaques during lipid-lowering. In mice with obesity and insulin resistance, we induced advanced plaques, then implemented lipid-lowering to promote atherosclerotic plaque inflammation-resolution. Concurrently, mice were treated with either platelet-depleting or control antibodies for 3 weeks. Platelet activation and insulin resistance were unaffected by lipid-lowering. Both antibody-treated groups showed reduced plaque macrophages, but plaque cellular and structural composition differed. In platelet-depleted mice, scRNA seq revealed dampened inflammatory gene expression in plaque macrophages and an expansion of a subset of Fcgr4+ macrophages having features of inflammation-resolving, phagocytic cells. Necrotic core size was smaller and collagen content greater, resembling stable human plaques. Consistent with the mouse results, clinical data showed that patients with lower platelet counts had decreased pro-inflammatory signaling pathways in circulating non-classical monocytes after lipid-lowering. These findings highlight that platelets hinder inflammation-resolution in atherosclerosis during lipid-lowering treatment. Identifying novel platelet-targeted therapies following lipid-lowering treatment in individuals with insulin resistance may be a promising therapeutic approach to promote atherosclerotic plaque inflammation-resolution.

Age-related inflammation or 'inflammaging' increases disease burden and controls lifespan. Adipose tissue macrophages (ATMs) are critical regulators of inflammaging; however, the mechanisms involved are not well understood in part because the molecular identities of niche-specific ATMs are unknown. Using intravascular labeling to exclude circulating myeloid cells followed by single-cell sequencing with orthogonal validation via multiparametric flow cytometry, we define sex-specific changes and diverse populations of resident ATMs through lifespan in mice. Aging led to depletion of vessel-associated macrophages, expansion of lipid-associated macrophages and emergence of a unique subset of CD38⁺ age-associated macrophages in visceral adipose tissue with inflammatory phenotype. Notably, CD169⁺CD11c^- ATMs are enriched in a subpopulation of nerve-associated macrophages (NAMs) that declines with age. Depletion of CD169⁺ NAMs in aged mice increases inflammaging and impairs lipolysis suggesting catecholamine resistance in visceral adipose tissue. Our findings reveal NAMs are a specialized ATM subset that control adipose homeostasis and link inflammation to tissue dysfunction during aging.