High-throughput, temporal and dose dependent, effect of vitamins and minerals on chondrogenesis

Tissue engineered hyaline cartilage is plagued by poor mechanical properties largely due to inadequate type II collagen expression. Of note, commonly used defined chondrogenic media lack 14 vitamins and minerals, some of which are implicated in chondrogenesis. Type II collagen promoter-driven Gaussia luciferase was transfected into ATDC5 cells to create a chondrogenic cell with a secreted-reporter. The reporter cells were used in an aggregate-based chondrogenic culture model to develop a high-throughput analytic platform. This high-throughput platform was used to assess the effect of vitamins and minerals, alone and in combination with TGFβ1, on type II collagen expression. Significant combinatorial effects between vitamins, minerals and TGFβ1 in terms of type II collagen expression and metabolism were discovered. An ‘optimal’ continual supplement of copper and vitamin K in the presence of TGFβ1 gave a 2.5-fold increase in collagen expression over TGFβ1 supplemented media alone.SummaryCurrent defined chondrogenic culture media lack several vitamins and minerals. Type II collagen is the quintessential marker of articular hyaline cartilage, and is commonly deficient in engineered tissue. A type II collagen promoter driven secreted luciferase construct has been transduced into ATDC5 cells and used to assess vitamin and mineral effects on chondrogenesis in a high-throughput format.

Activation of corticotropin releasing factor receptors up regulates collagen production by hepatic stellate cells via promoting p300 expression

Liver fibrosis is characterized with the over expression and excessive accumulation of extracellular matrix proteins, including collagens. The causative factors in the over production of collagens are not fully understood. This study aims to test a hypothesis that activation of corticotropin releasing factor receptors up regulates the expression of collagen in hepatic stellate cells. In this study, human hepatic stellate cell line, LX-2 cells were cultured. Expression of collagens by LX-2 cells was assessed by real time RT-PCR, Western blotting. The results showed that, upon exposure to urocortin in the culture, LX-2 cells (a human hepatic stellate cell line) increased the expression of collagen IV (Col4) markedly. The exposure to urocortin also enhanced the levels of pTip60, H3K9, RNA polymerase II and forkhead box protein 3 at the collagen promoter locus as well as increase in the expression of Col4 mRNA and protein in the cells. Blocking p300 efficiently suppressed the urocortin-induced Col4 expression in LX-2 cells and unveiled an apoptosis-inducing effect of urocortin. In conclusion, activation of CRF receptors is capable of enforcing the production of Col4 by LX-2 cells via up regulating the p300 pathway, which may contribute to the development of liver fibrosis.

Vitamin D Receptor in Osteoblasts Is a Negative Regulator of Bone Mass Control

The physiological and beneficial actions of vitamin D in bone health have been experimentally and clinically proven in mammals. The active form of vitamin D [1α,25(OH)2D3] binds and activates its specific nuclear receptor, the vitamin D receptor (VDR). Activated VDR prevents the release of calcium from its storage in bone to serum by stimulating intestinal calcium absorption and renal reabsorption. However, the direct action of VDR in bone tissue is poorly understood because serum Ca2+ homeostasis is maintained through tightly regulated ion transport by the kidney, intestine, and bone. In addition, conventional genetic approaches using VDR knockout (VDR-KO, VDR−/−) mice could not identify VDR action in bone because of the animals' systemic defects in calcium metabolism. In this study, we report that systemic VDR heterozygous KO (VDR+/L−) mice generated with the Cre/loxP system as well as conventional VDR heterozygotes (VDR+/−) showed increased bone mass in radiological assessments. Because mineral metabolism parameters were unaltered in both types of mice, these bone phenotypes imply that skeletal VDR plays a role in bone mass regulation. To confirm this assumption, osteoblast-specific VDR-KO (VDRΔOb/ΔOb) mice were generated with 2.3 kb α1(I)-collagen promoter-Cre transgenic mice. They showed a bone mass increase without any dysregulation of mineral metabolism. Although bone formation parameters were not affected in bone histomorphometry, bone resorption was obviously reduced in VDRΔOb/ΔOb mice because of decreased expression of receptor activator of nuclear factor kappa-B ligand (an essential molecule in osteoclastogenesis) in VDRΔOb/ΔOb osteoblasts. These findings establish that VDR in osteoblasts is a negative regulator of bone mass control.

Phosphorylation of Fli1 at Threonine 312 by Protein Kinase C δ Promotes Its Interaction with p300/CREB-Binding Protein-Associated Factor and Subsequent Acetylation in Response to Transforming Growth Factor β

ABSTRACT Previous studies have shown that transforming growth factor β (TGF-β)-induced collagen gene expression involves acetylation-dependent dissociation from the human α2(I) collagen (COL1A2) promoter of the transcriptional repressor Fli1. The goal of this study was to elucidate the regulatory steps preceding the acetylation of Fli1. We first showed that TGF-β induces Fli1 phosphorylation on a threonine residue(s). The major phosphorylation site was localized to threonine 312 located in the DNA binding domain of Fli1. Using several independent approaches, we demonstrated that Fli1 is directly phosphorylated by protein kinase C δ (PKC δ). Additional experiments showed that in response to TGF-β, PKC δ is recruited to the collagen promoter to phosphorylate Fli1 and that this step is a prerequisite for the subsequent interaction of Fli1 with p300/CREB-binding protein-associated factor (PCAF) and an acetylation event. The phosphorylation of endogenous Fli1 preceded its acetylation in response to TGF-β stimulation, and the blockade of PKC δ abrogated both the phosphorylation and acetylation of Fli1 in dermal fibroblasts. Promoter studies showed that a phosphorylation-deficient mutant of Fli1 exhibited an increased inhibitory effect on the COL1A2 gene, which could not be reversed by the forced expression of PCAF or PKC δ. These data strongly suggest that the phosphorylation-acetylation cascade triggered by PKC δ represents the primary mechanism whereby TGF-β regulates the transcriptional activity of Fli1 in the context of the collagen promoter.