Biology subjects

Lewis, K. T.

Publications and source records attributed to Lewis, K. T..

4 recordsLinked to original sources

bioRxiv2024

Control of Physiologic Glucose Homeostasis via the Hypothalamic Modulation of Gluconeogenic Substrate Availability

The brain augments glucose production during fasting, but the mechanisms are poorly understood. Here, we show that Cckbr-expressing neurons in the ventromedial hypothalamic nucleus (VMNCckbr cells) prevent low blood glucose during fasting through sympathetic nervous system (SNS)-mediated augmentation of adipose tissue lipolysis and substrate release. Activating VMNCckbr neurons mobilized gluconeogenic substrates without altering glycogenolysis or gluconeogenic enzyme expression. Silencing these cells (CckbrTetTox animals) reduced fasting blood glucose, impaired lipolysis, and decreased circulating glycerol (but not other gluconeogenic substrates) despite normal insulin, counterregulatory hormones, liver glycogen, and liver gluconeogenic gene expression. Furthermore, {beta}3-adrenergic adipose tissue stimulation in CckbrTetTox animals restored lipolysis and blood glucose. Hence, VMNCckbr neurons impact blood glucose not by controlling islet or liver physiology, but rather by mobilizing gluconeogenic substrates. These findings establish a central role for hypothalamic and SNS signaling during normal glucose homeostasis and highlight the importance of gluconeogenic substrate mobilization during physiologic fasting.

physiology↗

bioRxiv2023

SCD1 and monounsaturated lipids are required for autophagy and survival of adipocytes

Exposure of adipocytes to cool temperatures often found in the periphery of the body induces expression of Stearoyl-CoA Desaturase-1 (SCD1), an enzyme that converts saturated fatty acids to monounsaturated fatty acids. In this study, we employed Scd1 knockout cells and mouse models, along with pharmacological SCD1 inhibition, to investigate further the roles of SCD1 in adipocytes. Our study reveals that production of monounsaturated lipids by SCD1 is necessary for fusion of autophagosomes to lysosomes and that with a SCD1-deficiency, autophagosomes accumulate. In addition, SCD1-deficiency impairs lysosomal and autolysosomal acidification resulting in vacuole accumulation and eventual cell death. Blocking autophagosome formation or supplementation with monounsaturated fatty acids maintains vitality of SCD1-deficient adipocytes. Taken together, our results demonstrate that in vitro inhibition of SCD1 in adipocytes leads to autophagy-dependent cell death, and in vivo depletion leads to loss of bone marrow adipocytes.

molecular biology↗

bioRxiv2022

Lipolysis of bone marrow adipocytes is required to fuel bone and the marrow niche during energy deficits

To investigate roles for bone marrow adipocyte (BMAd) lipolysis in bone homeostasis, we created a BMAd-specific Cre mouse model in which we knocked out adipose triglyceride lipase (ATGL, Pnpla2). BMAd-Pnpla2-/- mice have impaired BMAd lipolysis, and increased size and number of BMAds at baseline. Although energy from BMAd lipid stores is largely dispensable when mice are fed ad libitum, BMAd lipolysis is necessary to maintain myelopoiesis and bone mass under caloric restriction. BMAd-specific Pnpla2 deficiency compounds the effects of caloric restriction on loss of trabecular bone, likely due to impaired osteoblast expression of collagen genes and reduced osteoid synthesis. RNA sequencing analysis of bone marrow adipose tissue reveals that caloric restriction induces dramatic elevations in extracellular matrix organization and skeletal development genes, and energy from BMAd is required for these adaptations. BMAd-derived energy supply is also required for bone regeneration upon injury, and maintenance of bone mass with cold exposure.

cell biology↗

bioRxiv2020

Cystic fibrosis transmembrane conductance regulator (CFTR) inhibition results in mucus accumulation in human airway epithelia Calu-3 cells: Experimental and Machine Learning Studies

Porosomes are cup-shaped lipoprotein structures at the cell plasma membrane involved in fractional release of intra-vesicular contents during secretion. At the base of the porosome facing the cell cytoplasm, secretory vesicles dock, fuse and swell, to release intra-vesicular content during secretion. Earlier studies demonstrate the cystic fibrosis trans-membrane conductance regulator (CFTR) associated with the porosome in human airways epithelial Calu-3 mucous-secreting cells, suggesting its possible involvement in porosome-mediated mucus secretion. The current study was undertaken to test this hypothesis. Electron microscopy followed by morphometric analysis using manual and computational machine learning approaches were used to assess changes in secretory vesicle size and content, following stimulation of secretion in the absence and presence of CFTR inhibitors. Results from the study demonstrate that stimulated Calu-3 cells pre-exposed to CFTR inhibitors, demonstrate attenuation of secretory vesicle swelling and the release of mucin. Consequently, accumulation of intracellular mucin is observed in cells exposed to CFTR inhibitors. These results further suggest that mucin secretion from Calu-3 cells involve CFTR both at the secretory vesicle membrane to regulate vesicle volume and hydration, and at the porosome to facilitate mucin hydration and secretion. These new findings progress our understanding of the involvement of CFTR on mucus hydration and secretion, providing critical insights into the etiology of CF disease.

cell biology↗