Deciphering the chromatin organization and epigenomics involved in adipocyte differentiation and hypertrophy by multimodal nanoscopy.

Abstract

The adipose tissue is the physiological energy reservoir for the whole body, but it also acts as a central metabolic organ in the regulation of body energy homeostasis. In particular, fat is stored in adipocytes inside cytosolic lipid droplets (LDs). Adipocyte hypertrophy occurring in obesity refers to an increase in adipocyte size due to LD enlargement. We aim to investigate the nuclear architecture and epigenetics during adipocyte differentiation and hypertrophy using an in vitro model of 3T3-L1 pre-adipocytes firstly differentiated into mature adipocytes, then cultured with fatty acids to induce hypertrophy. On pre-adipocytes, mature and hypertrophic adipocytes, we assessed lipid accumulation as a hypertrophy marker. Chromatin plays a central role in controlling gene expression under different physiological and pathological mechanisms. We employed optical nanoscale microscopy, such as confocal, super-resolution stimulation emission depletion (STED), and molecular biology analyses (ELISA), to assess the remodeling of nuclear architecture, chromatin organization, and epigenetic modifications associated with adipocyte differentiation and hypertrophy. Confocal and STED analyses showed appreciable differences in nuclear architecture, chromatin condensation, distribution, and chromatin methylation/acetylation among pre-adipocytes, mature and hypertrophic adipocytes. Moreover, we quantified the average changes in the DNA methylation (5-methylcytosine) by ELISA immunoassay. These preliminary results indicate epigenome and nuclear organization remodeling during adipocyte differentiation and hypertrophy. We can conclude that nuclear architecture remodeling is a significant and central factor in the genome function regulation.