IGF-binding protein-5 (IGFBP-5) is produced by porcine embryonic myogenic cell (PEMC) cultures and is secreted into the medium. IGFBP-5 may play some role in myogenesis and/or in changes in myogenic cell proliferation that accompany differentiation. IGFBP-5 reportedly may either suppress or stimulate proliferation or differentiation of cultured cells depending on cell type and culture conditions. Additionally, IGFBP-5 has been shown to possess both IGF-dependent and IGF-independent actions in some cell types. The goal of this study was to produce recombinant porcine IGFBP-5 (rpIGFBP-5) and assess its IGF-I-dependent and IGF-I-independent actions on the proliferation of PEMCs. To accomplish this, we have expressed porcine IGFBP-5 in the baculovirus system, purified and characterized the expressed rpIGFBP-5 and produced an anti-porcine IGFBP-5 antibody that neutralizes the biological activity of porcine IGFBP-5. rpIGFBP-5, purified to 98% homogeneity using nickel affinity chromatography and IGF-I affinity chromatography, suppressed IGF-I-stimulated proliferation of PEMCs in a concentration-dependent manner (P>0.05). rpIGFBP-5 also suppressed Long-R3-IGF-I-stimulated proliferation of PEMCs (P>0.05), even in the presence of significant molar excess of Long-R3-IGF-I compared with rpIGFBP-5, demonstrating the IGF-independent activity that rpIGFBP-5 possesses in PEMCs, since Long-R3-IGF-I is an IGF analog that has very low affinity for the IGFBPs but retains its ability to bind to the type I IGF receptor and thereby can stimulate proliferation. The anti-rpIGFBP-5 IgY produced against rpIGFBP-5 specifically recognized native porcine IGFBP-5 in PEMC media that also contained porcine IGFBP-2, -3, and -4. This antibody is capable of neutralizing the effects of both rpIGFBP-5 and endogenously produced porcine IGFBP-5 on PEMCs as well as detecting IGFBP-5 in Western blots. The production of rpIGFBP-5 and a neutralizing antibody to porcine IGFBP-5 provides a powerful tool to investigate the role of IGFBP-5 in porcine myogenic cell proliferation and differentiation. The data provided here demonstrated that IGFBP-5 has the potential to affect proliferation of PEMCs during critical periods of in vitro muscle cell development and therefore may impact the capacity for ultimate postnatal muscle mass development in vivo.
M S Pampusch, G Xi, E Kamanga-Sollo, K J Loseth, M R Hathaway, W R Dayton and M E White
W Yin, D Liao, M Kusunoki, S Xi, K Tsutsumi, Z Wang, X Lian, T Koike, J Fan, Y Yang and C Tang
The synthetic compound NO-1886 (ibrolipim) is a lipoprotein lipase activator that has been proven to be highly effective in lowering plasma triglycerides. Recently, we found that NO-1886 also reduced plasma free fatty acids and glucose in high-fat/high-sucrose diet-induced diabetic rabbits. In the current study, we investigated the effects of NO-1886 treatment on ectopic lipid deposition and the islet pathology in miniature swine fed a high-fat/high-sucrose diet. Our results showed that feeding this diet to miniature swine caused insulin resistance, increased lipid deposition in non-adipose tissue, such as in the heart, skeletal muscle, liver and pancreas, and also caused pancreatic beta cell damage. However, supplementing 1% NO-1886 (200 mg/kg per day) into the high-fat/high-sucrose diet decreased ectopic lipid deposition, improved insulin resistance, and alleviated the beta cell damage. These results suggest that improvement of lipid disorder, non-adipose tissue steatosis and insulin resistance may be very important for the protection of beta cell damage. Therefore, NO-1886 is potentially beneficial for the treatment of insulin-resistance syndrome.