(DCP005) CHARACTERIZATION OF HEALTHY AND OBESE ADIPOSE TISSUE REMODELLING BY 3D IMAGING AND SINGLE CELL ANALYSIS

Background: Vascular endothelial growth factor A (VEGFA) stimulates angiogenesis and plays a pivotal role in adipose tissue. Our previous work demonstrated that adipose tissue-derived VEGFA (adipose-VEGF) induces brown fat-like changes to white adipose tissue (WAT) and angiogenesis with reduced inflammation via M2-like polarization of macrophages, contributing to healthy adipose remodelling and improved glucose homeostasis. Additionally, adipose-VEGF can enhance nerve fibre growth within WAT, critical for promoting metabolic homeostasis. In contrast, adipose-VEGF deletion will lead to impaired glucose tolerance and insulin resistance. Neurovascular remodelling of adipose tissue is therefore crucial in conferring the metabolic benefits observed. In this study, we are investigating the effects of high-fat diet-induced obesity on adipose tissue remodelling, redefining healthy vs unhealthy adipose tissue in terms of its neurovascular architecture and immune cell heterogeneity.

METHODS AND RESULTS: A diet-induced obesity C57BL/6 mice model was established on a 20-week high-fat diet (HFD) regimen, and metabolic monitoring through weekly bodyweight measurements, intraperitoneal glucose and insulin tolerance test were conducted. As anticipated, the HFD-fed group demonstrated insulin resistance and dysglycemia. Immunolabeling and three-dimensional imaging, via the Adipo-Clear tissue clearing method, enables in-depth visualization of the angioarchitecture and nerve fibres of the entire visceral WAT (perigonal WAT or PWAT), a critical focus of this study due to its significant association with insulin resistance. High-dimensional mass cytometry (CyTOF) on harvested PWAT showed a decrease in the proportion of M2-like macrophages in the HFD compared to the normal diet group. This analysis also revealed other changes in cellular heterogeneity, including a reduction in eosinophils and ILC2. In addition, gene expression analysis showed elevated inflammation levels and the downregulation of VEGF and neurotrophic factor neuregulin 4 in response to HFD. This suggests a potential reduction in sympathetic innervation and vascular density, which will be further confirmed by quantification of nerve fibre and blood vessel density.

Conclusion: AT plays a crucial role in systemic metabolic regulation, where the adipose tissue quality, rather than quantity, is essential in supporting its functions. This study characterizes the architecture of healthy adipose tissue at multiple scales, from the neurovascular network down to a single-cell resolution. The unhealthy nature of adipose tissue is manifested by a shift from a type 2 immune response known to mitigate adipose tissue inflammation to a more pro-inflammatory microenvironment. By investigating the structural changes of adipose tissue under obesity, we hope to further understand its effects on the whole-body metabolism of obese patients, a significant factor for developing type-2 diabetes.