Adipose Tissue CTGF Expression is Associated with Adiposity and Insulin Resistance in Humans

Abstract

Objective: Connective tissue growth factor (CTGF) is an important regulator of fibrogenesis in many organs. This study evaluated the interrelationship among adipose tissue CTGF expression, fat mass, and insulin resistance in humans.

Methods: This study examined (1) CTGF gene expression in human subcutaneous preadipocytes before and after inducing adipogenesis; (2) relationships among abdominal subcutaneous adipose tissue CTGF gene expression, body fat mass, and indices of insulin sensitivity, including the hepatic insulin sensitivity index and the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotope glucose tracer infusion, in 72 people who had marked differences in adiposity and insulin sensitivity; (3) localization of CTGF protein in subcutaneous adipose tissue; and (4) effect of progressive (5%, 11%, and 16%) weight loss on adipose tissue CTGF gene expression.

Results: CTGF was highly expressed in preadipocytes, not adipocytes. Adipose tissue CTGF expression was strongly correlated with body fat mass and both skeletal muscle and liver insulin sensitivity, and CTGF-positive cells were predominantly found in areas of fibrosis. Progressive weight loss caused a stepwise decrease in adipose tissue CTGF expression.

Conclusions: It was concluded that increased CTGF expression is associated with adipose tissue expansion, adipose tissue fibrosis, and multi-organ insulin resistance in people with obesity.

Trial registration: ClinicalTrials.gov NCT01184170 NCT01299519 NCT00981500 NCT01104220.

Conflict of interest statement

Disclosure: The authors declare no conflict of interest.

© 2019 The Obesity Society.

Figures

Figure 1.. CTGF is highly expressed in human subcutaneous preadipocytes, compared to mature adipocytes.

(A) Gene expression of connective tissue growth factor (CTGF) and adiponectin (ADIPOQ) was determined in human subcutaneous preadipocytes before (D0) and 8 days (D8) after induction of adipogenesis (n=4). (B) Microarray dataset obtained from the Gene Expression Omnibus (GEO) database (GSE8995) were used to evaluate CTGF and ADIPOQ expression in stromal vascular fraction (SVF) cells and adipocytes isolated from human subcutaneous adipose tissue samples (n=6). Data were log-transformed for the statistical analysis and back-transformed for presentation. Data are means ± SEM. *Value significantly different from D0 or SVF value, P<0.001.

Figure 2.. Adipose tissue CTGF gene expression is associated with adiposity and insulin resistance.

Relationships between adipose tissue CTGF gene expression and body mass index (BMI) (A), fat mass (B), fasting plasma insulin concentration (C), Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (D), hepatic insulin sensitivity index (HISI) (E), and insulin-stimulated increases (%) in glucose rate of disappearance (Rd) (F) in men (black circles, n=14) and women (white circles, n=58). Pearson’s correlation coefficient (r) and P values for all subjects (n=72) are provided in each plot.

Figure 3.. Increased CTGF protein expression is associated with adipose tissue fibrosis.

(A) Western blot analysis of CTGF in subcutaneous abdominal adipose tissue and bar graph showing CTGF and its fragments (between 20 and 37 kDa) normalized to GAPDH in participants who were lean or obese (n=4–5 per group). Data are means ± SEM. *Value significantly different from lean value, P<0.01. (B) Masson’s trichrome staining and CTGF immunostaining of subcutaneous abdominal adipose tissue obtained from people who are lean and those with obesity. A negative control for CTGF staining was obtained by omitting the primary antibody. Scale bar: 500 μm.

Figure 4.. Effect of diet-induced progressive weight loss on adipose tissue CTGF gene expression in people with obesity.

Adipose tissue CTGF gene expression was determined before and after progressive 5%, 11%, and 16% weight loss or before and after 6 months of weight maintenance in people with obesity (n=9 per group). Data were log-transformed for statistical analysis and back-transformed for presentation. Data are means ± SEM. #Significant linear effect of time during progressive weight loss, P<0.05. *Value significantly different from before value, P<0.05.