Faculty Bibliography

The mammalian brain is the most cholesterol-rich organ of the body, relying on in situ de novo cholesterol synthesis. Maintaining cholesterol homeostasis is crucial for normal brain function. Oxysterol-binding protein (OSBP)-related proteins (ORPs) are highly conserved cytosolic proteins that coordinate lipid homeostasis by regulating cell signaling, inter-organelle membrane contact sites, and non-vesicular transport of cholesterol. Here, we show that ORP6 is highly enriched in the mammalian brain, particularly within neurons and astrocytes, with widespread expression across distinct brain regions, including the hippocampus, which is essential for learning and memory. Whole-body ablation of ORP6 (Osbpl6^-/-) in mice resulted in dysregulation of systemic and brain lipid homeostasis, with elevated levels of brain desmosterol and amyloid-beta oligomers (AβOs). Mechanistically, ORP6 knockdown in astrocytes altered the expression of cholesterol metabolism genes, promoting the accumulation of esterified cholesterol in lipid droplets, reducing cholesterol efflux and plasma membrane cholesterol content, and increasing amyloid-beta precursor protein (APP) processing. Our findings underscore the role of ORP6 in systemic and brain lipid homeostasis, highlighting its importance in maintaining overall brain health.

BACKGROUND/UNASSIGNED:Electronic cigarettes (e-cigarettes) are the most used tobacco product among youth, and adults who smoke combustible cigarettes favor e-cigarettes over approved cessation aids. Despite the lower perceived harm of vaping compared with smoking, acute inhalation of e-cigarette aerosol elicits cardiovascular responses that may lead to persistent damage when repeated over time. METHODS/UNASSIGNED:We exposed female hypercholesterolemic mice to either pod-mod e-cigarette aerosol or filtered air daily for 24 weeks. We assessed the long-term effects of vaping on aortic stiffness and vasoreactivity while investigating the underlying cellular and molecular mechanisms of injury. RESULTS/UNASSIGNED:Chronic inhalation of e-cigarette aerosol triggered the accumulation of inflammatory signals systemically and within aortic tissues, as well as T-lymphocyte accrual in the aortic wall. Limited eNOS (endothelial nitric oxide synthase) expression and enhanced superoxide radical production curbed NO bioavailability in the aorta of mice exposed to e-cigarette aerosol despite iNOS (inducible nitric oxide synthase) induction, impairing the endothelium-dependent vasodilation that regulates blood flow distribution. Inhalation of e-cigarette aerosol thickened and stiffened aortic tissues via collagen deposition and remodeling, hindering the storage of elastic energy and limiting the cyclic distensibility that enables the aorta to function as a pressure reservoir. These effects combined contributed to raising systolic and pulse pressure above control levels. CONCLUSIONS/UNASSIGNED:Chronic inhalation of aerosol from pod-mod e-cigarettes promotes oxidative stress, inflammation, and fibrosis within aortic tissues, significantly impairing passive and vasoactive aortic functions. This evidence provides new insights into the biological processes that increase the risk of adverse cardiovascular events as a result of pod-mod e-cigarette vaping.

After birth, tissues grow until they reach adult size, with each organ exhibiting unique cellular dynamics, growth patterns, and stem or non-stem cell sources. Using multiscale experimental and computational approaches, we found that aortic enlargement follows distinct growth principles, scaling with the vertebral column. Expansion proceeds via two temporally coordinated, spatially stochastic waves of proliferation aligned with blood flow, each with unique cell-cycle kinetics, with the first wave featuring cycles as short as 6 h. Single-cell RNA sequencing revealed increased fatty acid metabolism accompanying cell enlargement. Mathematical modeling and experiments showed that endothelial cell extrusion is essential for maintaining homeostatic aortic size as it adjusts for proliferation excess. Using a genetic model of achondroplasia, we mechanistically demonstrated that the aorta preserves proper scaling by increasing cell extrusion while keeping proliferation rates intact. These findings provide a blueprint of the principles orchestrating aortic growth, which relies entirely on the proliferation of resident differentiated cells. A record of this paper's transparent peer review process is included in the supplemental information.

Decreased brain levels of coenzyme Q₁₀ (CoQ₁₀), an endogenously synthesized lipophilic antioxidant^1,2, underpin encephalopathy in primary CoQ₁₀ deficiencies^3,4 and are associated with common neurodegenerative diseases and the ageing process^5,6. CoQ₁₀ supplementation does not increase CoQ₁₀ pools in the brain or in other tissues. The recent discovery of the mammalian CoQ₁₀ headgroup synthesis pathway, in which 4-hydroxyphenylpyruvate dioxygenase-like protein (HPDL) makes 4-hydroxymandelate (4-HMA) to synthesize the CoQ₁₀ headgroup precursor 4-hydroxybenzoate (4-HB)⁷, offers an opportunity to pharmacologically restore CoQ₁₀ synthesis and mechanistically treat CoQ₁₀ deficiencies. To test whether 4-HMA or 4-HB supplementation promotes CoQ₁₀ headgroup synthesis in vivo, here we administered 4-HMA and 4-HB to Hpdl^-/- mice, which model an ultra-rare, lethal mitochondrial encephalopathy in humans. Both 4-HMA and 4-HB were incorporated into CoQ₉ and CoQ₁₀ in the brains of Hpdl^-/- mice. Oral treatment of Hpdl^-/- pups with 4-HMA or 4-HB enabled 90-100% of Hpdl^-/- mice to live to adulthood. Furthermore, 4-HB treatment stabilized and improved the neurological symptoms of a patient with progressive spasticity due to biallelic HPDL variants. Our work shows that 4-HMA and 4-HB can modify the course of mitochondrial encephalopathy driven by HPDL variants and demonstrates that CoQ₁₀ headgroup intermediates can restore CoQ₁₀ synthesis in vivo.

While weight loss is highly recommended for those with obesity, >60% will regain their lost weight. This weight cycling is associated with elevated risk of cardiovascular disease, relative to never having lost weight. How weight loss/regain directly influence atherosclerotic inflammation is unknown. Thus, we studied short-term caloric restriction (stCR) in obese hypercholesterolemic mice, without confounding effects from changes in diet composition. Weight loss was found to promote atherosclerosis resolution independent of plasma cholesterol. From single-cell RNA-sequencing and subsequent mechanistic studies, this can be partly attributed to a unique subset of macrophages accumulating with stCR in epididymal white adipose tissue (eWAT) and atherosclerotic plaques. These macrophages, distinguished by high expression of Fcgr4, help to clear necrotic cores in atherosclerotic plaques. Conversely, weight regain (WR) following stCR accelerated atherosclerosis progression with disappearance of Fcgr4+ macrophages from eWAT and plaques. Furthermore, WR caused reprogramming of immune progenitors, sustaining hyper-inflammatory responsiveness. In summary, we have developed a model to investigate the inflammatory effects of weight cycling on atherosclerosis and the interplay between adipose tissue, bone marrow, and plaques. The findings suggest potential approaches to promote atherosclerosis resolution in obesity and weight cycling through induction of Fcgr4+ macrophages and inhibition of immune progenitor reprogramming.

Cellular senescence is an irreversible state of cell cycle arrest with a complex role in tissue repair, aging, and disease. However, inconsistencies in identifying cellular senescence have led to varying conclusions about their functional significance. We developed a machine learning-based approach that uses nuclear morphometrics to identify senescent cells at single-cell resolution. By applying unsupervised clustering and dimensional reduction techniques, we built a robust pipeline that distinguishes senescent cells in cultured systems, freshly isolated cell populations, and tissue sections. Here we show that this method reveals dynamic, age-associated patterns of senescence in regenerating skeletal muscle and osteoarthritic articular cartilage. Our approach offers a broadly applicable strategy to map and quantify senescent cell states in diverse biological contexts, providing a means to readily assess how this cell fate contributes to tissue remodeling and degeneration across lifespan.

Chemotherapy-induced alopecia and radiation-induced alopecia, the thinning or loss of hair due to cytotoxic chemotherapy and radiation therapy, respectively, are distressing adverse effects of cancer treatment. Chemotherapy, targeted therapies, and radiation therapy used in pediatric oncology often lead to alopecia by damaging hair follicles, with varying degrees of severity depending on the specific treatment type, mechanism of action, and damage-response pathway involved. Pediatric chemotherapy-induced alopecia, radiation-induced alopecia, and permanent alopecia, defined as hair regrowth that remains incomplete 6 months or more after treatment, have significant negative impacts on mental health, self-esteem, and social interactions, highlighting the need for further research into supportive care strategies. There are currently no standard interventions for chemotherapy-induced alopecia or radiation-induced alopecia in children, with most recommendations limited to gentle hair care and camouflaging techniques during treatment. Scalp cooling has demonstrated safety and efficacy in reducing chemotherapy-induced alopecia in adults and is currently under investigation in children and adolescents. Topical and low-dose oral minoxidil have been studied in children for other hair loss disorders and may improve hair regrowth after chemotherapy or radiation. Increased awareness and continued research into management strategies for pediatric chemotherapy-induced alopecia and radiation-induced alopecia are necessary to help mitigate its significant negative impact on quality of life.

Skin, hair, and eye (oculocutaneous) color is due to melanin, a pigment produced by melanocytes. This review considers processes required for pigmentation and the complex genetic network that regulates them. The first requisite is migration of neural crest-derived melanoblasts, which populate various embryonic sites, then differentiate into melanocytes or seed stem cell niches. Differentiation is marked by expression of genes essential for melanogenesis, which takes place in melanosomes and involves conversion of tyrosine into melanin. Melanosome biogenesis requires premelanosome maturation through coordinated delivery of melanogenic enzymes such as tyrosinase (TYR), structural proteins, and transporters that establish an intraluminal environment conducive to melanogenesis. Sorting of proteins through endolysosomal pathways and delivery to melanosomes is facilitated by trafficking protein complexes. Finally, melanin is transferred to keratinocytes to protect against ultraviolet light. Numerous pigment-related disorders result from disruption of these pathways, including Waardenburg syndrome caused by melanoblast migration disruption, oculocutaneous albinism presenting with absent/reduced melanogenesis, and melanoma resulting from dysregulation of proliferation/survival. Genetic variants also determine normal color variation, which is pronounced across populations that, historically, lived in different geographical regions. This variation, shaped by genetic factors, environmental influences, and evolutionary pressures, underpins the wide range of pigmentation phenotypes seen today.

Atherosclerotic cardiovascular diseases (ASCVD) remain the leading cause of death globally. Animal and human studies link psychological stress-related disorders to ASCVD. Despite this accumulating evidence linking stress to increased cardiovascular disease (CVD) risk, it remains unclear whether stress impairs the benefits of standard risk-reduction therapies, of which lipid-lowering remains the most common, or whether this increased risk is driven by systemic inflammatory states. We tested the hypothesis that psychological stress limits the benefits of lipid lowering on resolving inflammation in atherosclerotic plaques by combining two established mouse models, namely one in which levels of atherogenic LDL cholesterol (LDL-C) can be lowered after plaques develop, and the other a model of chronic social defeat stress (CSDS). Here we show that mice susceptible to CSDS ("SUS") had attenuated benefits of LDL-C lowering compared to control (CON) or resilient (RES) mice. Moreover, in SUS mice (vs. CON or RES) there was heightened inflammation in the plaque macrophages, with evidence that this was a result of re-programming in the bone marrow (BM) of the precursors of macrophages, namely monocytes. Remarkably, these observations aligned with human imaging studies, in which LDL-C lowering therapy was not as effective in reducing either systemic or arterial inflammation in subjects with higher (vs. lower) neural imaging measures of psychological stress. In summary, the integration of the mouse model and human data provides important mechanistic and clinical insights into the crucial role of chronic stress in ASCVD, highlighting that this common risk factor impairs the anti-atherosclerotic benefits of lipid-lowering medications and may represent an important determinant of residual ASCVD risk.

Ulcerative colitis is an idiopathic, chronic inflammatory bowel disease. Its pathogenesis is multifactorial involving inflammation and immune dysregulation. Proinflammatory TNFα/NFκB signaling is believed to play a cardinal role in ulcerative colitis. Growing evidence indicates the molecular interactions between the cellular metabolites and different phases of inflammation. This study aims to identify the metabolites that can inhibit TNFα/NFκB signaling and are potentially therapeutic against various TNFα-associated inflammatory diseases, particularly inflammatory bowel diseases. We performed in vitro and in vivo screening of cellular metabolites to inhibit TNFα/NFκB signaling. Multiple confirmation assays, including NFκB translocation, quantitative real-time PCR, ELISA, immunofluorescence staining, and RNA sequencing analysis were executed. Drug affinity-responsive target stability assay with proteomics was utilized for target identification. cPLA2 ablated mice with dextran sodium sulfate-induced colitis were employed to assess pyruvate's dependence on its molecular target in attenuating ulcerative colitis pathogenesis. Metabolite screening and subsequent validation with multiple approaches led to the isolation of pyruvate, a glycolytic metabolite, and a critical node in several metabolic pathways, as a novel inhibitor of TNFα/NFκB signaling. Importantly, pyruvate suppressed inflammation, preserved colonic histology, maintained tight junction proteins, and regulated permeability in the ulcerative colitis model. Additionally, cPLA2 was identified as a previously unknown target of pyruvate and pyruvate largely lost its therapeutic effects against ulcerative colitis in cPLA2-deficient mice. Conclusively, this study not only unveils pyruvate as an antagonist of TNFα/NFκB signaling and therapeutic intervention against colitis but also provides mechanistic insight into the mode of action of pyruvate.