A stimulatory TSH receptor antibody enhances adipogenesis via phosphoinositide 3-kinase activation in orbital preadipocytes from patients with Graves' ophthalmopathy

Abstract

Graves' ophthalmopathy (GO) is characterized by expanded volume of the orbital tissues associated with elevated serum levels of TSH receptor (TSHR) autoantibodies. Because previous studies have demonstrated evidence of adipogenesis within the GO orbit, we sought to determine whether M22, a human monoclonal antibody directed against TSHR, enhances adipogenesis in orbital fibroblasts from patients with GO and, if so, to identify signaling mechanisms involved. GO orbital fibroblast cultures (n=10) were treated for 10 days with bovine TSH (1 or 10·0 U/l) or M22 (1 or 10 ng/ml) in serum-free adipocyte differentiation medium. Some cultures also received a phosphoinositide 3-kinase (PI3K) inhibitor or an inhibitor of cAMP production. In other experiments, confluent cultures (n=8) were treated for between 1 and 30 min with TSH (0·1–10·0 U/l) or M22 (0·1–100 ng/ml) with measurement of cAMP production or levels of phosphorylated AKT (pAKT). We found levels of adiponectin, leptin, and TSHR mRNA to be increased in GO cultures treated for 10 days with either M22 (2·6 mean fold ±0·7; P=0·03) or TSH (13·2±5·8-fold, P=0·048). In other studies, M22 and TSH stimulated cAMP production and pAKT levels in GO cells. Inhibition of PI3K activity during 10 days in culture decreased the levels of M22-stimulated mRNA encoding adiponectin (67±12%; P=0·021), as well as adiponectin and CCAAT/enhancer-binding protein α protein levels. In conclusion, M22 is a pro-adipogenic factor in GO orbital preadipocytes. This antibody appears to act via the PI3K signaling cascade, suggesting that inhibition of PI3K signaling may represent a potential novel therapeutic approach in GO.

Forkhead Transcription Factor FOXO1 Is Regulated by Both a Stimulatory Thyrotropin Receptor Antibody and Insulin-Like Growth Factor-1 in Orbital Fibroblasts from Patients with Graves' Ophthalmopathy

“…In those studies, as in the present study, PI3K inhibition by LY290042 was less efficient. In conjunction with previous work in which PI3K/pAKT signaling was demonstrated to be involved in both adipogenesis and HA secretion in GO orbital fibroblasts (3,4), these results are compatible with both cellular processes being regulated by FOXO1 in these cells.…”

“…As in Graves' hyperthyroidism, the thyrotropin receptor (TSHR) has been identified as a primary target antigen in GO, and autoantibodies directed against this receptor appear to play a direct role in disease development (2). TSHR activation by TSHR antibodies (TSAb) in cultured orbital fibroblasts results in both increased HA production and enhanced adipogenesis (3)(4)(5)(6). Occurring within the orbit, these altered 1 Division of Pediatric Endocrinology and Metabolism; 2 Division of Endocrinology, Diabetes, Metabolism and Nutrition; Mayo Clinic, Rochester, Minnesota.…”

Role of miR-146a in the Regulation of Inflammation in an In Vitro Model of Graves' Orbitopathy

“…Recently, a cAMP-independent cascade was shown to increase PI3K activity, a signaling pathway that plays a central role in the pathogenesis of GO. 31 Kumar et al 31 reported that a stimulatory TSH receptor antibody enhanced adipogenesis via PI3K activation in GO, and suggested that inhibition of PI3K signaling may represent a potential novel therapeutic approach in GO.…”

Serum Adiponectin Levels and Changes in Glucose Metabolism before and after Treatment for Thyroid Dysfunction

“…Various explanations for this discrepancy have been suggested. One possible explanation involves the induction of TSH receptors on adipose cells via the effects of TSH-stimulating antibodies, thus resulting in increased adiponectin production (38). Direct stimulation of adiponectin by thyroid hormones through the peroxisome proliferator-activated receptor (PPAR) signaling pathway is another hypothesis (39,40).…”