SMAD2 and SMAD3 differentially regulate adiposity and the growth of subcutaneous white adipose tissue

Abstract

Adipose tissue is the primary site of energy storage, playing important roles in health. While adipose research largely focuses on obesity, fat also has other critical functions, producing adipocytokines and contributing to normal nutrient metabolism, which in turn play important roles in satiety and total energy homeostasis. SMAD2/3 proteins are downstream mediators of activin signaling, which regulate critical preadipocyte and mature adipocyte functions. Smad2 global knockout mice exhibit embryonic lethality, whereas global loss of Smad3 protects mice against diet‐induced obesity. The direct contributions of Smad2 and Smad3 in adipose tissues, however, are unknown. Here, we sought to determine the primary effects of adipocyte‐selective reduction of Smad2 or Smad3 on diet‐induced adiposity using Smad2 or Smad3 “floxed” mice intercrossed with Adiponectin‐Cre mice. Additionally, we examined visceral and subcutaneous preadipocyte differentiation efficiency in vitro. Almost all wild type subcutaneous preadipocytes differentiated into mature adipocytes. In contrast, visceral preadipocytes differentiated poorly. Exogenous activin A suppressed differentiation of preadipocytes from both depots. Smad2 conditional knockout (Smad2cKO) mice did not exhibit significant effects on weight gain, irrespective of diet, whereas Smad3 conditional knockout (Smad3cKO) male mice displayed a trend of reduced body weight on high‐fat diet. On both diets, Smad3cKO mice displayed an adipose depot‐selective phenotype, with a significant reduction in subcutaneous fat mass but not visceral fat mass. Our data suggest that Smad3 is an important contributor to the maintenance of subcutaneous white adipose tissue in a sex‐selective fashion. These findings have implications for understanding SMAD‐mediated, depot selective regulation of adipocyte growth and differentiation.

Single-cell analysis of white adipose tissue reveals the tumor-promoting adipocyte subtypes

“…However, the Areg subpopulation mA7 also showed increased transcriptional diversity, which suggested a dedifferentiation potential [ 30 ]. In addition, Smad3, an important contributor to the maintenance of WAT, is active in mA1 cells [ 31 ]. mA2 highly express Etv4, which has been reported to enhance morphological differentiation in preadipocytes [ 32 ] (Fig.…”

Single-cell analysis of white adipose tissue reveals the tumor-promoting adipocyte subtypes

“…However, the Areg subpopulation, mA7 also showed increased transcriptional diversity, which suggested a dedifferentiation potential [28]. Besides, Smad3, an important contributor to the maintenance of WAT, was active in mA1 [29]. mA2 highly expressed Etv4 which are reported to enhance morphological differentiation in preadipocytes [30] (Figure 2H).…”

Obesity, bone marrow adiposity, and leukemia: Time to act

“…Furthermore, loss of function mutation in ALK7 or ACVR1C in humans reduces the risk of obesity, metabolic disorders, and cardiovascular disease (CVD) risk 296 . Activin C (ActC) is a ligand for ALK7 and their interaction on mature adipocytes elicits a SMAD2/3 response such as increased adiposity and growth of SC WAT (SCWAT) in a sex‐dependent manner in mice 297,298 . Hence, it is critical to understand the impact of BM‐As and WAT‐As differentially to dig out their different roles in leukemia, including ALL and AML.…”