Cross-anatomical single-cell definition and characterization of human adipose progenitor niche

Adipose tissue is a key metabolic and highly-dynamic organ whose dysregulation may cause clinical conditions of concern such as obesity and lipodystrophy. Its function varies based on the anatomy, in fact, visceral adipose tissue expansion carries a greater risk of life-threatening associated comorbidities than subcutaneous expansion. Among the responsible for adipose tissue plasticity are the adipose-derived stem and progenitor cells (ASPCs) which can commit to form new mature adipocytes even in a post-developmental adult organism. The advent of scRNA-seq techniques allowed to deline-ate a clear and unbiased picture of the murine ASPC landscape across depots, unraveling subpopulations with distinct functional properties and even non- and anti-adipogenic features, however a similar depth of understanding is still lack-ing in humans. This work focuses on defining the human ASPC niche composition and equilibrium across four different depots (Subcuta-neous (SC), Omental (OM), Perirenal (PR) and Mesocolic (MC)) and over more than 75 individuals of various BMIs. We took advantage of bulk and scRNA-seq techniques to explore hASPC heterogeneity then functionalize our findings in vitro over 30 donors. We found that two main populations, the highly-proliferative adipose stem cells and highly-adipogenic pre-adipocytes, are ubiquitously present in all analyzed depots but their relative proportions display a depot-specific and BMI-dependent distribution. Despite their omnipresence, these subpopulations still exhibited depot-specific gene expression patterns, likely reflecting distinct AT properties. Five minor subpopulations are also shared across depots and have specific gene expression patterns resembling populations previously described in mice. We further identified two OM-specific meso-thelial cell populations, cobblestone in morphology, out of which one highly expresses and secretes IGFBP2 (Insulin-like growth factor binding protein 2). This OM-specific IGFBP2+ population constitutes 2-5% of the non-immune, non-endothelial OM stromal vascular fraction depending on the donor's BMI, appears to transition between mesothelial and mesenchymal cell states and inhibits the adipogenic capacity of hASPCs in a depot-specific manner through IGFBP2 secre-tion and integrin receptor signaling. Altogether, our in-depth characterization of hASPC heterogeneity and function not only highlights the cellular uniqueness of different adipose niches but also identifies a new mechanism underlying the limited adipogenic capacity of OM hASPCs by uncovering an OM-specific IGFBP2+ mesothelial-like cell population that negatively regulates hASPC adipogenesis through IGFBP2 signaling. Further dissecting the precise mechanism of negative regulation in adipogenesis may lead to the discovery of new druggable targets to combat excessive adipose tissue expansion.