Hypertrophied human adipocyte spheroids asin vitromodel of weight gain and adipose tissue dysfunction

Abstract

The rise in obesity prevalence has created an urgent need for new and improved methods to study human adipocytes and the pathogenic effects of weight gain in vitro. Despite numerous studies showing the advantages of culturing adipocyte progenitors as 3D structures, the majority continue using traditional 2D cultures which result in small, multilocular adipocytes with poor representability. We hypothesized that providing differentiating pre-adipocytes with a vascular growth niche would mimic in vivo adipogenesis and improve the differentiation process. Here we present a simple, easily applicable culture protocol that allows for the differentiation and culturing of human adipocytes with a more unilocular morphology and larger lipid droplets than previous protocols. We moreover offer a protocol for inducing adipocyte enlargement in vitro, resulting in larger lipid droplets and development of several key features of adipocyte dysfunction, including altered adipokine secretions and impaired lipolysis. Taken together, our hypertrophied human adipocyte spheroids offer an improved culture system for studying the cellular and molecular mechanisms causing metabolic dysfunction and inflammation during weight gain.

What's up with WAT: attempting to mimic adipose tissue in vitro

“…Adipogenesis occurred along the vasculature, and prevention of vascular sprouting significantly reduced spheroid growth. Traditional two-dimensional cell culture and spheroids grown without Matrigel did not result in vasculature development and produced much smaller spheroids and adipocytes (Ioannidou et al 2022). Taken together, the HUVAS method developed in the current report (Ioannidou et al 2022) improves on many key features of WAT biology, including vasculature, extra cellular matrix, large unilocular adipocytes and adipokine secretion.…”

“…Another effect of obesity-associated WAT inflammation is that basal lipolysis is increased but resistant to stimulated lipolysis (Crewe et al 2017;Stenkula & Erlanson-Albertsson, 2018). Importantly, both increased basal lipolysis and impaired stimulated lipolysis were apparent in hypertrophied HUVAS (Ioannidou et al 2022). Additionally, WAT insulin resistance hinders the ability of insulin to suppress lipolysis and stimulate fatty acid and glucose uptake, ultimately contributing to systemic metabolic dysfunction.…”

“…WAT is at the forefront of the obesity crisis, so ways of accurately mimicking WAT hypertrophy are needed to understand the mechanistic changes associated with this state. In this regard, Ioannidou et al (2022) show that lipids can be used to produce adipocyte and lipid droplet hypertrophy in HUVAS. To do this, the authors used Intralipid, which is a mixture of various fatty acids (monoand poly-unsaturated and saturated) and cholesterol as distinct from most studies, which use a single, usually saturated, fatty acid, which is less physiological and can have unintended inflammatory consequences.…”

“…The authors describe a way to mimic obesity-associated adipocyte hypertrophy and subsequent cellular dysfunction. This new model is called human unilocular vascularized adipocyte spheroids (HUVAS) and represents a major advancement in the ability to perform mechanistic in vitro analysis of human WAT in health and obesity (Ioannidou et al 2022).…”

“…Inflammation is one of the early responses to hypertrophy and results partly from the accumulation and activation of macrophages, which secrete inflammatory cytokines like interleukin-6 and monocyte chemotactic protein-1. These inflammatory responses were evident in hypertrophied HUVAS (Ioannidou et al 2022), but the macrophage response is unclear and would be interesting to explore since SVF used to differentiate HUVAS would contain immune cells.…”