Biology subjects

Sembrat, J. C.

Publications and source records attributed to Sembrat, J. C..

4 recordsLinked to original sources

bioRxiv2024

SenSet, a novel human lung senescence cell gene signature, identifies cell-specific senescence mechanisms

Cellular senescence is a major hallmark of aging. Senescence is defined as an irreversible growth arrest observed when cells are exposed to a variety of stressors including DNA damage, oxidative stress, or nutrient deprivation. While senescence is a well-established driver of aging and age-related diseases, it is a highly heterogeneous process with significant variations across organisms, tissues, and cell types. The relatively low abundance of senescence in healthy aged tissues represents a major challenge to studying senescence in a given organ, including the human lung. To overcome this limitation, we developed a Positive-Unlabeled (PU) learning framework to generate a comprehensive senescence marker gene list in human lungs (termed SenSet) using the largest publicly available single-cell lung dataset, the Human Lung Cell Atlas (HLCA). We validated SenSet in a highly complex ex vivo human 3D lung tissue culture model subjected to the senescence inducers bleomycin, doxorubicin, or irradiation, and established its sensitivity and accuracy in characterizing senescence. Using SenSet, we identified and validated cell-type specific senescence signatures in distinct lung cell populations upon aging and environmental exposures. Our study presents the first comprehensive analysis of senescent cells in the healthy aging lung and uncovers cell-specific gene signatures of senescence, presenting fundamental implications for our understanding of major lung diseases, including cancer, fibrosis, chronic obstructive pulmonary disease, or asthma.

genomics↗

bioRxiv2021

GPER-dependent estrogen signaling increases cardiac GCN5L1 expression and MCAD activity

Reversible lysine acetylation regulates the activity of cardiac metabolic enzymes, including those controlling fuel substrate metabolism. Mitochondrial-targeted GCN5L1 and SIRT3 have been shown to regulate the acetylation status of mitochondrial enzymes, which results in alterations to the relative oxidation rates of fatty acids, glucose, and other fuels for contractile activity. However, the role that lysine acetylation plays in driving metabolic differences between male and female hearts is not currently known. In this study, we report that estrogens induce the expression of GCN5L1 via GPER agonism in cardiac cells, which increases the enzymatic activity and acetylation status of the fatty acid oxidation enzyme medium chain acyl-CoA dehydrogenase (MCAD).

physiology↗

bioRxiv2021

Cardiomyocyte BRAF and type 1 RAF inhibitors promote cardiomyocyte and cardiac hypertrophy in mice in vivo

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade promotes cardiomyocyte hypertrophy and is cardioprotective, with the three RAF kinases forming a node for signal integration. Our aims were to determine if BRAF is relevant for human heart failure, if BRAF promotes cardiomyocyte hypertrophy, and if Type 1 RAF inhibitors developed for cancer (that paradoxically activate ERK1/2 at low concentrations: the "RAF paradox") may have the same effect. BRAF was upregulated in heart samples from patients with heart failure compared with normal controls. We assessed the effects of activated BRAF in the heart using mice with tamoxifen-activated Cre for cardiomyocyte-specific knock-in of the activating V600E mutation into the endogenous gene. We used echocardiography to measure cardiac dimensions/function. Cardiomyocyte BRAFV600E induced cardiac hypertrophy within 10 d, resulting in increased ejection fraction and fractional shortening over 6 weeks. This was associated with increased cardiomyocyte size without significant fibrosis, consistent with compensated hypertrophy. The experimental Type 1 RAF inhibitor, SB590885, and/or encorafenib (a RAF inhibitor used clinically) increased ERK1/2 phosphorylation in cardiomyocytes, and promoted hypertrophy, consistent with a "RAF paradox" effect. Both promoted cardiac hypertrophy in mouse hearts in vivo, with increased cardiomyocyte size and no overt fibrosis. In conclusion, BRAF potentially plays an important role in human failing hearts, activation of BRAF is sufficient to induce hypertrophy, and Type 1 RAF inhibitors promote hypertrophy via the "RAF paradox". Cardiac hypertrophy resulting from these interventions was not associated with pathological features, suggesting that Type 1 RAF inhibitors may be useful to boost cardiomyocyte function.

biochemistry↗

bioRxiv2021

CD4+ T cell lymphopenia and dysfunction in severe COVID-19 disease is autocrine TNF-α/TNFRI-dependent

Lymphopenia is common in severe COVID-19 disease, yet the mechanisms are poorly understood. In 148 patients with severe COVID-19, we found lymphopenia was associated with worse survival. CD4+ lymphopenia predominated, with lower CD4+/CD8+ ratios in severe COVID-19 compared to recovered, mild disease (p<0.0001). In severe disease, immunodominant CD4+ T cell responses to Spike-1(S1) produced increased in vitro TNF-, but impaired proliferation and increased susceptibility to activation-induced cell death (AICD). CD4+TNF-+ T cell responses inversely correlated with absolute CD4+ counts from severe COVID-19 patients (n=76; R=-0.744, P<0.0001). TNF- blockade including infliximab or anti-TNFRI antibodies strikingly rescued S1-specific CD4+ proliferation and abrogated S1-AICD in severe COVID-19 patients (P<0.001). Single-cell RNAseq demonstrated downregulation of Type-1 cytokines and NF{kappa}B signaling in S1-stimulated CD4+ cells with infliximab treatment. Lung CD4+ T cells in severe COVID-19 were reduced and produced higher TNF- versus PBMC. Together, our findings show COVID-19-associated CD4+ lymphopenia and dysfunction is autocrine TNF-/TNFRI-dependent and therapies targeting TNF- may be beneficial in severe COVID-19. One Sentence SummaryAutocrine TNF-/TNFRI regulates CD4+ T cell lymphopenia and dysfunction in severe COVID-19 disease.

immunology↗