Functional characterization of murine Adipogenesis regulatory cells and remodeling of inguinal adipose tissue during early postnatal development

Adipose tissue is a dynamic endocrine and metabolic organ whose cellular composition is regulated by a hierarchy of adipose stem and progenitor cells (ASPCs). These include adipogenesis regulatory cells (Aregs) which are a distinct stromal subpopulation defined by the expression of Fmo2, Tspan11 and Meox2. These cells resist adipogenesis and actively inhibit the differentiation of otherwise adipogenic cells through paracrine mechanisms. Despite this well-established role, the emergence of this identity and the signals that drive it remain unknown.

This thesis addresses these questions across two chapters. Chapter 2 is based on a published study and provides a molecular and functional characterisation of Aregs in adult mouse inguinal white adipose tissue (ingWAT). Using multi-omic profiling, in vitro differentiation assays and in vivo Matrigel implantation models, we demonstrate that Aregs are robustly non- and anti-adipogenic across diverse experimental conditions, mouse strains and sexes. This inhibitory capacity is mediated by secreted factors such as CD142, MGP, and GDF10 acting together with the retinoic acid (RA) signalling pathway. Exposure of CD142- ASPCs (ASPCs depleted from Aregs) to active Aregs shifts their transcriptional state toward an Areg-like one, suggesting this paracrine signal leads to a conversion. Importantly, this phenotype emerges in an age-dependent manner with the non-adipogenic phenotype of Aregs being absent before postnatal day 16 (P16) and fully established by postnatal week 4.

Chapter 3 characterises when and how this age-dependent transition occurs. Areg maturation is not driven by gut microbiota colonisation, nor can it be explained by chronological age alone. Early weaning accelerates the Areg non-adipogenic phenotype in a weight-gain-dependent manner, identifying adipose tissue remodelling as a candidate to drive this switch. Single nucleus RNAsequencing of ingWAT resolved beige-to-white adipocyte transition at a subcluster resolution and reveals, through pseudotime analysis, that Aregs come from a bifurcation of the ASC lineage at the preadipocyte stage. The spatial proximity of Aregs to sympathetic nerve fibres and their selective expression of neurotrophins receptors raises the hypothesis that neuro-adipose interactions may be at the root of Aregs’ maturation.

Together these findings establish a developmental framework for Areg identity and position their maturation as an integral part of postnatal ingWAT remodelling.