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

BACKGROUND: 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. METHODS: 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. RESULTS: SFTPD gene was expressed in human adipose tissue and adipocytes. This expression was decreased in OM and SC adipose tissue from obese subjects with (similar to 47%, P<0.0001; and similar to 37%, P = 0.048) and without (similar to 34%, P = 0.001; and similar to 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. CONCLUSIONS: Both OM and SC adipose tissue (mainly mature adipocytes) express SFTPD. This expression decreases with obesity and impaired glucose tolerance.