Biology subjects

Tu, L. N.

Publications and source records attributed to Tu, L. N..

3 recordsLinked to original sources

bioRxiv2025

TSPO deficiency reveals a novel role for porphyrins in regulating white adipose tissue lipid metabolism

The translocator protein (TSPO) is a mitochondrial outer membrane protein with high expression in cells specialized for lipid metabolism, including white adipose tissue (WAT), where its physiological function remains poorly defined. Our previous work demonstrated a role for TSPO in mitochondrial fatty acid oxidation, prompting us to investigate its contribution to adipocyte lipid homeostasis under metabolic stress. We employed a combination of in vivo and in vitro approaches using global Tspo knockout (Tspo-/-) mice, primary adipocyte cultures, and pharmacological TSPO-binding drugs to examine TSPO function. We show that Tspo-/- mice exhibited increased WAT mass and adipocyte hypertrophy following high-fat diet feeding, with no changes in caloric intake. These changes were accompanied by suppression of key lipolytic genes, reduced circulating NEFA and glycerol levels, and altered expression of fatty acid oxidation genes. Lipidomic profiling showed no genotype-dependent changes, indicating impaired mobilization rather than altered lipid composition. In vitro, TSPO deficiency enhanced lipid accumulation during adipocyte diberentiation and impaired expression of lipolytic genes. TSPO-binding drugs phenocopied this response in TSPO-expressing cells. Mechanistically, we identify protoporphyrin IX (PPIX), an endogenous TSPO ligand, as a suppressor of adipogenic and lipolytic programs. PPIX levels increase during adipogenesis, and its accrual inhibits both lipid accumulation and lipolytic response, whereas hemin does not elicit these ebects. Our findings identify TSPO as a regulator of adipocyte lipid metabolism through a previously unrecognized TSPO-PPIX axis that influences lipid mobilization in adipocytes. This mechanism provides insight into TSPOs role in metabolic adaptation and highlights its potential as a therapeutic target in obesity-associated adipose dysfunction.

pathology↗

bioRxiv2023

Monocyte Adhesion and Transmigration Through Endothelium Following Cardiopulmonary Bypass Shearing is Mediated by IL-8 Signaling

BackgroundThe use of cardiopulmonary bypass (CPB) can induce sterile systemic inflammation that contributes to morbidity and mortality, especially in children. Patients have been found to have increased expression of cytokines and transmigration of leukocytes during and after CPB. Previous work has demonstrated that the supraphysiologic shear stresses present during CPB are sufficient to induce proinflammatory behavior in non-adherent monocytes. The interactions between shear stimulated monocytes and vascular endothelial cells have not been well studied and have important translational implications. MethodsTo test the hypothesis that non-physiological shear stress experienced by monocytes during CPB affects the integrity and function of the endothelial monolayer via IL-8 signaling pathway, we have used an in vitro CPB model to study the interaction between THP-1 monocyte-like cells and human neonatal dermal microvascular endothelial cells (HNDMVECs). THP-1 cells were sheared in polyvinyl chloride (PVC) tubing at 2.1 Pa, twice of physiological shear stress, for 2 hours. Interactions between THP-1 cells and HNDMVECs were characterized after coculture. ResultsWe found that sheared THP-1 cells adhered to and transmigrated through the HNDMVEC monolayer more readily than static controls. When co-culturing, sheared THP-1 cells also disrupted in the VE-cadherin and led to reorganization of cytoskeletal F-actin of HNDMVECs. Treating HNDMVECs with IL-8 resulted in upregulation of vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) while also increasing the adherence of non-sheared THP-1 cells. Preincubating HNDMVECs with Reparixin, an inhibitor of CXCR2/IL-8 receptor inhibited sheared THP-1 cell adhesion to the HNDMVECs. ConclusionsThese results suggested that IL-8 not only increases the endothelium permeability during monocyte migration, but also affects the initial adhesion of monocytes in a CPB setup. This study revealed a novel mechanism of post-CPB inflammation and will contribute to the development of targeted therapeutics to prevent and repair the damage to neonatal patients. HighlightsO_LIShear stress in a CPB-like environment promoted the adhesion and transmigration of monocytes to and through endothelial monolayer. C_LIO_LITreating endothelial monolayer with sheared monocytes led to disruption of VE-cadherin and reorganization of F-actin. C_LIO_LIInteraction between sheared monocytes resulted in a significant increase of IL-8 release. C_LIO_LIInhibiting IL-8 receptor prevented sheared monocyte adhesion, while IL-8 promoted naive monocyte adhesion. C_LI

cell biology↗

bioRxiv2022

Hemodynamic stress activates inflammatory responses and cell death through spectrin-dependent modulation of Store Operated Calcium Entry

Patients undergoing cardiac surgery face significant inflammatory induced by exposure to cardiopulmonary bypass (CPB), contributing to heightened morbidity and mortality. The molecular and cellular mechanisms that underpin this inflammatory process remain unknown. To address this knowledge gap, we performed snRNA/ATAC-Sequencing on leukocytes from neonatal CPB patients. Classical monocytes become more prevalent and have dysregulation of inflammatory genes after CPB, indicating their role in CPB-associated inflammation. A genome-wide CRISPR screen and in vitro experiments in non-adherent monocytic cells identified two novel genes, SPTAN1 and RAF1, as effectors of hemodynamic stress. SPTAN1 and RAF1 activate store-operated calcium entry that results inflammation and cell death. snATAC-Seq revealed dynamically changing patterns of chromatin accessibility and AP-1 transcription factor binding after CPB exposure. These findings provide novel insights into the pathogenesis of CPB-associated inflammation, with broad implications for understanding the early stages of sterile inflammation and how non-adherent cells sense shear stress.

cell biology↗