The Mechanism of Dietary Protein Modulation of Bone Metabolism via Alterations in Members of the GH/IGF Axis.

Dietary protein intake as a critical regulatory factor of bone metabolism is a vital element to regulate nutritional status of mammals. Under the action of protease, dietary protein is digested into peptides and free amino acids (FAAs). Then, the metabolites are absorbed by enterocytes and metabolized in various organs of mammals. The dietary protein intake regulates bone metabolism generally via two aspects, dietary itself and signaling transduction. At the dietary level, different kinds of amino acids (AAs) of dietary protein may affect various protein metabolism of bone by regulating proteasome depending on proteolysis and protein synthesis. In addition, dietary protein from multiple sources such as animal, vegetal and healthcare products, presents distinct influences on bone metabolism via regulating calcium balance; At the cellular level, these products can regulate several biological functions via regulating signaling transduction. For example, the significant member of growth hormone/insulin-like growth factor (GH/IGF) axis can be regulated by dietary protein, which has an influence on bone metabolism through different approaches. This review mainly discusses the relationship between dietary protein and GH/IGF axis and illustrates the regulation of bone metabolism in mammals by dietary protein and its signaling transduction.

Linkage disequilibrium and functional analysis of PRE1 insertion together with SNPs in the promoter region of IGFBP7 gene in different pig breeds.

Polymorphisms in regions upstream of transcription initiation site may modify the transcriptional activity of target genes by changing promoter activity. This study aims to determine whether or not polymorphisms at porcine IGFBP7 promoter region affect gene expression. In this study, eight SNPs and one PRE1 insertion in this region were first confirmed. The PRE1 insertion was widespread in 20 Chinese indigenous breeds, but was not observed in three commercial breeds. A perfect linkage disequilibrium, consisting of six of those SNPs and a PRE1, was observed with two haplotypes (h1 and h2) in five pig breeds. The h1 haplotype had an overwhelming superiority distribution in Large White, Landrace, and Bama mini-pig; in turn, the h2 only existed in the PRE1 presence breeds. As the haplotypes and PRE1 were located at gene promoter regions, we further investigated the transfection of plasmids with three different fragments of IGFBP-7 promoter region (H1, H2, RF). The CMV promoter of the pEGFP-N1 was substituted by these three different fragments, respectively. Different transcriptional and translational activities of EGFP in PK-15 cells were observed in these three recombinant plasmids by quantitative real-time PCR and flow cytometric analysis. The results indicated that H1 had the higher transcriptional and translational activities of EGFP as compared to the H2 (P < 0.05, P < 0.05). As compared to the RF group, EGFP mRNA expression level was significantly higher in H1 groups (P < 0.05). The IGFBP-7 promoter polymorphisms detected in this study may be important functional variants and potential genetic markers for pig population genetic study.