Locally Produced IGF-1by Orbital Fibroblasts As Implicative Pathogenic Factor For Patients With Thyroid Associated Ophthalmopathy

Background:To explore the expression of insulin-like growth factor-1(IGF-1) receptor by orbital fibroblasts (OF) from patients with thyroid associated ophthalmopathy (TAO) and its effect in the pathogenesis of TAO. To determine the correlation between clinical activity scores (CAS) of TAO patients and their locally produced and/or systemically circulating IGF-1, and to assess the possible pathogenic role of IGF-1in TAO.Methods:Human OF were harvested and cultured from the connective tissue of patients who were finally diagnosed as TAO and ordinary patients as controls. The expression of IGF-1Rof OF was detected by confocal microscopy and flow cytometry, then comparing and analyzing the expression of IGF-1R between patients with TAO and controls by statistical method. Eighteen patients with TAO, and16age-and gender-matched controls were included in the present study. Among them, orbital tissue surgically collected from five TAO patients and five healthy controls was used for OF culture and in vitro study. Total and free IGF-1in serum levels were determined by an ELISA kit for all the participants in this study. The IGF-1concentration in culture media of OFs was determined using a noncompetitive time-resolved radioimmunoassay kit. The effect of octreotide (OCT), a somatostatin analog, on proliferation of OFs was assessed using the MTT assay. IGF-1mRNA levels were measured by real-time polymerase chain reaction (PCR).Results: The expression of IGF-1R by OF from TAO patients (72.6%±10.4) was significantly different comparing with controls (27.8%±10.7, P<0.05). After observation and quantitative analyzing by confocal microscopy, we found IGF-1R was over expressed by OF of TAO patients than normal controls and this receptor was mainly located in the ambient of nucleus and cytoplasm. Cultured OFs from both TAO patients and normal donors secreted IGF-1, and the secretion continued over a72hour period in vitro. IGF-1secretion by OFs was elevated in the TAO group. Both the elevated secretion of IGF-1and proliferation of OFs from TAO patients could be inhibited by OCT. Result of quantitative PCR showed that IGF-1mRNA expression by OFs in TAO patients was up-regulated more than2-fold compared with normal controls (P<0.05), and this up-regulation was prevented by OCT treatment. Total and free serum IGF-1levels in TAO patients were similar to those of normal controls. However, the IGF-1level in cultured medium of OFs from TAO patients, but not serum levels of IGF-1, was positively correlated with CAS (r=00.97, P=00.017).Conclusions:IGF-R is over expressed by OF from TAO patients compared with control donors in vitro. Local production of IGF-1by cultured OFs may be positively correlated with CAS, whereas systemically circulating IGF-1may remain unchanged in TAO patients. Thus, locally produced IGF-1may develop a role in the pathogenesis of TAO in an autocrine or paracrine fashion. The inhibitory effect of OCT on proliferating and IGF-1mRNA levels of cultured OFs from TAO patients may be used as the mechanistic explanation for somatostatin analog as a valuable option in the treatment of TAO.