Defining the mechanisms regulating adipose tissue metabolic memory and its role in rebound weight gain. - Obesity is one of the most pressing public health challenges of the 21st century. Weight gain occurs in the setting of nutrient excess, which stimulates adipose tissue expansion via both healthy hyperplastic and pathologic hypertrophic processes. The metabolic consequences of obesity, including diabetes and fatty liver disease, stem from a relative deficiency in hyperplastic expansion of adipocyte progenitor cells. GLP1 medications have drastically changed the therapeutic landscape, enabling millions of patients to achieve significant weight loss, however much remains to be learned about the pathophysiology of obese and post- weight loss adipose. Using single-cell sequencing we identified a population of maladaptive FAPs arising in obese adipose as well as an anatomically-distinct population of connective-tissue-resident macrophages marked by Lyve1. Preliminary data indicate that the Lyve1+ macrophages serve as niche-defining cells that maintain FAP homeostasis in lean adipose, however their number are diminished in obesity. Genetic depletion of Lyve1+ macrophages leads to pathologic lineage allocation of maladaptive FAPs, that express a transcriptional profile analogous to obesity-induced FAPs, including the matrix-modifying genes such as Timp1. We discovered corresponding ECM stiffening and decreased compositional diversity in obesity using highly precise rheological quantification and ECM proteomics of mouse and human adipose. We developed a tunable ex vivo 3D collagen hydrogel model and found that FAP adipogenic differentiation capacity is tightly regulated by ECM biomechanics. Most notably, many of the cellular changes and ECM properties induced by obesity persist following weight loss. The Aims of this grant are to: (1) Determine the role of Lyve1+ macrophage in directing the lineage allocation of maladaptive FAPs in obesity and weight loss. (2) Characterize the activity of FAP-expressed Timp1 in maladaptive ECM remodeling and its consequences for post-weight loss adipose physiology. To attain these objectives, we will utilize novel mouse models, advanced transcriptomic techniques, metabolic and biomechanical phenotyping to investigate of the mechanisms regulating the development of adipose ECM-encoded “metabolic memory” of previous obesity that persists despite subsequent weight loss. This work will address long-standing questions in the field regarding adipose-intrinsic cellular and molecular mechanisms promoting rebound weight gain.
