The lung innate immune gene surfactant protein-D is expressed in adipose tissue and linked to obesity status

Abstract

Surfactant protein-D (SFTPD) is a component of the lung innate immunity that enhances clearance of pathogens and modulates inflammatory responses. An inverse association of putative, lung-derived circulating SFTPD with obesity has been reported but no information is available concerning possible SFTPD gene expression in human adipose tissue. SFTPD gene expression was analyzed in human omental (OM; n=156) and subcutaneous (SC; n=106) adipose tissue, and in isolated fat cells (n=12) in association with measures of obesity and glucose tolerance. SFTPD gene was expressed in human adipose tissue and adipocytes. This expression was decreased in OM and SC adipose tissue from obese subjects with (-47%, P<0.0001; and -37%, P=0.048) and without (-34%, P=0.001; and -22%, P=0.08; respectively) type 2 diabetes when compared with the control group. Indeed, OM SFTPD was inversely associated with body mass index (r=-0.33, P<0.0001), percent fat mass (r=-0.36, P<0.0001), waist perimeter (r=-0.26, P=0.002), diastolic blood pressure (r=-0.21, P=0.018) and fasting glucose (r=-0.21, P=0.012); and positively linked to the expression of insulin receptor substrate 1 (IRS1; r=0.25, P=0.004), perilipin A (PLIN; r=0.38, P=0.007) and fatty acid synthase (FASN; r=0.36, P<0.0001). Accordingly, increased SFTPD (4.5-fold, P=0.02) was detected in isolated adipocytes when compared with the stromal-vascular cell fraction, in parallel to IRS1, FASN and PLIN. Both OM and SC adipose tissue (mainly mature adipocytes) express SFTPD. This expression decreases with obesity and impaired glucose tolerance.