The Adipose Tissue Microenvironment Regulates Depot-Specific Adipogenesis in Obesity

Abstract

The sexually dimorphic distribution of adipose tissue influences the development of obesity-associated pathologies. The accumulation of visceral white adipose tissue (VWAT) that occurs in males is detrimental to metabolic health, while accumulation of subcutaneous adipose tissue (SWAT) seen in females may be protective. Here, we show that adipocyte hyperplasia contributes directly to the differential fat distribution between the sexes. In male mice, high-fat diet (HFD) induces adipogenesis specifically in VWAT, while in females HFD induces adipogenesis in both VWAT and SWAT in a sex hormone-dependent manner. We also show that the activation of adipocyte precursors (APs), which drives adipocyte hyperplasia in obesity, is regulated by the adipose depot microenvironment and not by cell-intrinsic mechanisms. These findings indicate that APs are plastic cells, which respond to both local and systemic signals that influence their differentiation potential independent of depot origin. Therefore, depot-specific AP niches coordinate adipose tissue growth and distribution.

Figure 1. Adipocyte hyperplasia contributes to depot- and sex-specific WAT growth in obesity

(A) Body fat as a percentage of total body weight after 8 weeks of SD or HFD feeding in male and female C57Bl/6J Adiponectin-creER; mTmG mice as measured by magnetic resonance imaging. (B) Weight of individual fat pads from male or female C57Bl/6J Adiponectin-creER; mTmG mice after 8 weeks of SD or HFD feeding. (In A and B, n = 9–15) (C) Experimental design for Adiponectin-creER; mTmG adipogenesis experiments. (D–E) Representative confocal images (left) and quantification (right) of adipocyte labeling in the indicated depots of Adiponectin-creER; mTmG male (D) or female (E) mice. (Males: n = 4–6. Females: n = 12–15) (F–G) Average adipocyte diameter of tdTomato+ (new) and eGFP+ (old) adipocytes from the indicated groups. (n = 4–6) Note: all data from A-E are from tamoxifen-treated animals. Significance was determined by comparing the indicated groups using an unpaired two-tailed student’s t-test. Scale bar is 100μM. Error bars represent mean ± S.E.M. See also Figure S1.

Figure 2. Fat pad weight and adipocyte precursor activation mirror depot-specific patterns of adipogenesis

(A–D) Correlation between adipogenesis and fat pad weight in the indicated depots of male (AB) or female (C–D) mice. Each point represents one mouse. (n = 21–26) (E) Representative flow cytometry plots to measure BrdU incorporation into adipocyte precursors. (F) BrdU incorporation into APs from the indicated depot of female mice following one week of SD or HFD and BrdU treatment. (n = 5 per group) (G) BrdU incorporation into adipocyte nuclei as measured via immunofluorescence in paraffin sections following one week of BrdU treatment (pulse) and 7 more weeks of the indicated diet (chase). (n = 8–10) (H–I) BrdU incorporation into APs from the indicated depot of ovariectomized female (H) or estrogen-treated male (I) mice following one week of SD or HFD and BrdU treatment. (n = 5–10) Significance in A–D was determined using Spearman’s non-parametric two-tailed correlation analysis. Significance in F–I was determined by comparing the indicated groups using an unpaired two-tailed student’s t-test. Error bars represent mean ± S.E.M. See also Figure S2.

Figure 3. Adipocyte precursor activation at the onset of obesity is determined by the adipose depot microenvironment

(A) Experimental design for AP transplant experiment. (B–C) Representative flow cytometry histogram (B) and dot plot (C) demonstrating engraftment of donor-derived tdTomato+ APs in the recipient depot, and BrdU incorporation into both tdTomato− and tdTomato+ populations. (D–E) BrdU incorporation into APs in donor, endogenous, or contralateral populations after 1 week of the indicated diet and BrdU treatment. (n = 3–8) Astrisks indicate significance over SD controls. Significance was determined using one-way ANOVA. Error bars represent mean ± S.E.M. See also Figure S3.

Figure 4. High-fat diet induced adipogenesis of adipocyte precursors is determined by the adipose depot microenvironment

(A) Experimental design for AP transplant experiment. (B) Representative images of mice with luminescent signal overlay following luciferase injection at the indicated time following transplant of APs from the SWAT of leptin-luciferase; mTmG mice. (C) Quantification of luminescent signal at the indicated experimental time points following transplant of APs from the SWAT of leptin-luciferase; mTmG mice. (n = 12) (D) Representative image of VWAT depot with luminescent overlay showing the region with luciferase activity in the left pad where the transplant was performed. (E) Representative confocal images of the luminescent region in (D) showing tdTomato+ mature adipocytes with LipidTOX staining (yellow crosses) adjacent to endogenous tdTomato− adipocytes (white asterisks). Exposure time for each luminescent image was 1 minute. Scale bar is 100μM. Significance was determined using an unpaired two-tailed student’s t-test. Error bars represent mean ± S.E.M. See also Figure S4.