3D analysis of the whole subcutaneous adipose tissue reveals a complex spatial network of interconnected lobules with heterogeneous browning ability

Abstract

Adipose tissue, as the main energy storage organ and through its endocrine activity, is interconnected with all physiological functions. It plays a fundamental role in energy homeostasis and in the development of metabolic disorders. Up to now, this tissue has been analysed as a pool of different cell types with very little attention paid to the organization and putative partitioning of cells. Considering the absence of a complete picture of the intimate architecture of this large soft tissue, we developed a method that combines tissue clearing, acquisition of autofluorescence or lectin signals by confocal microscopy, segmentation procedures based on contrast enhancement, and a new semi-automatic image analysis process, allowing accurate and quantitative characterization of the whole 3D fat pad organization. This approach revealed the unexpected anatomic complexity of the murine subcutaneous fat pad. Although the classical picture of adipose tissue corresponds to a superposition of simple and small ellipsoidal lobules of adipose cells separated by mesenchymal spans, our results show that segmented lobules display complex 3D poly-lobular shapes. Despite differences in shape and size, the number of these poly-lobular subunits is similar from one fat pad to another. Finally, investigation of the relationships of these subunits between each other revealed a never-described organization in two clusters with distinct molecular signatures and specific vascular and sympathetic nerve densities correlating with different browning abilities. This innovative procedure reveals that subcutaneous adipose tissue exhibits a subtle functional heterogeneity with partitioned areas, and opens new perspectives towards understanding its functioning and plasticity.

From whole-organ imaging to in-silico blood flow modeling: A new multi-scale network analysis for revisiting tissue functional anatomy

“…Hence, functional clustering reveals the existence of an unexpected organization scale inside large clusters. Consistent with our previous reports [47] [48], this finding clearly emphasizes the heterogeneity of adipose tissue and its multiscale organization particularly for the oxidative metabolism point of view that strongly depends on vasculature and perfusion.…”

“…Furthermore, various structural graph properties (such as centrality and authority) were strongly correlated with local anatomic features (vascular density, vessel connections) as well as functional features (total blood perfusion and exchange flux perfusion time). The primacy of these vascular-based network parameters near the lymph node region is highly associated with the high browninggene expression found in [48], thus corroborating the well-described relationships between vascularization and the browning process. Hence, we found a vascular-based body of evidence for the existence of a central, well-perfused, strongly-connected and, highly-coupled region of adipose tissue as opposed to the more unstructured, poorly-connected, peripheral organization.…”

“…These entities have been found to concentrate adipocytes having discriminant browning (ability to turn into brown fat) potential [47]. The biological analysis of these entities was refined in [48] with micro-dissection and immuno-labeling showing different expression levels of browning genes and mitochondrial apparatus in the core region as compared with the periphery, but also strong heterogeneity in adipocyte browning abilities within the core of the fat pad. As found in [47] and [48], here we reveal a central region located near the lymph node where structural entities have been identified, and a peripheral region with no particular structural units.…”

Specific Biological Features of Adipose Tissue, and Their Impact on HIV Persistence

“…These immune clusters provided the first evidence of a direct role of fat immune cells in anti-infectious responses, and also highlight the "regionalization" of AT. In fact, AT is a vascularized tissue that is organized into several lobular unit (Tang et al, 2008;Walker et al, 2008;Chi et al, 2018;Dichamp et al, 2019). These partitioned areas exhibit specific metabolic (and probably immune) activities.…”

The Involvement of Neuroimmune Cells in Adipose Innervation

“…while others have shown that browning commonly occurs around LNs (61). Furthermore, all lymph nodes in the body are surrounded by adipose tissue, which is activated during an immune response (62).…”