The requirement for RNA synthesis in the differentiation of cultured chick embryo chondrocytes

Chondrogenesis and cartilage tissue engineering: the longer road to technology development

Joint injury and disease are painful and debilitating conditions affecting a substantial proportion of the population. The idea that damaged cartilage in articulating joints might be replaced seamlessly with tissue-engineered cartilage is of obvious commercial interest because the market for such treatments is large. Recently, a wealth of new information about the complex biology of chondrogenesis and cartilage has emerged from stem cell research, including increasing evidence of the role of physical stimuli in directing differentiation. The challenge for the next generation of tissue engineers is to identify the key elements in this new body of knowledge that can be applied to overcome current limitations affecting cartilage synthesis in vitro. Here we review the status of cartilage tissue engineering and examine the contribution of stem cell research to technology development for cartilage production.

Esculetin suppresses proteoglycan metabolism by inhibiting the production of matrix metalloproteinases in rabbit chondrocytes

The possible mechanism of the chondroprotective effect of 6,7-dihydroxycoumarin (esculetin) was investigated using primary cultures of rabbit articular chondrocytes. Esculetin (EST) significantly suppressed the proteoglycan depletion and the release of pulse-labeled [35S]proteoglycan from the matrix layer of rabbit chondrocytes treated with recombinant human interleukin-1alpha. The matrix metalloproteinase inhibitor, 1,10-phenanthroline, also blocked the proteoglycan depletion and [35S]proteoglycan release. From these results, it is likely that recombinant human interleukin-1alpha-induced proteoglycan depletion is mediated by matrix metalloproteinases. Although esculetin did not directly inhibit collagenolytic activity in the culture media, it significantly suppressed the production of pro-matrix metalloproteinase-1/interstitial procollagenase and pro-matrix metalloproteinase-3/prostromelysin 1, accompanied by a decrease in the steady-state levels of their mRNAs. These results suggest that esculetin is a therapeutically effective candidate for inhibition of cartilage destruction in osteoarthritis and rheumatoid arthritis.

Regulation of glycosaminoglycan synthesis by parathyroid hormone and prostaglandin E2 in cultured dental pulp cells

The effects of parathyroid hormone (PTH) and prostaglandin E2 (PGE2) on glycosaminoglycan (GAG) synthesis in bovine dental pulp cells were studied. Dibutyryl cyclic adenosine 3',5'-monophosphate and isobutyl methylxanthine were used to assess whether their effects were mediated by intracellular cAMP. Glycosaminoglycan synthesis was assayed by measuring [35S]sulfate incorporation into the GAG fraction of dental pulp cells. Glycosaminoglycan synthesis was increased 1.3-fold by PTH (4 units per ml) alone, 1.6-fold by PTH in the presence of isobutyl methylxanthine, 1.2-fold by PGE2 (100 ng per ml) alone, and 1.5-fold by PGE2 in the presence of isobutyl methylxanthine. Dibutyryl cyclic adenosine 3',5'-monophosphate enhanced GAG synthesis in a concentration-dependent manner and mimicked the effects of PTH and PGE2. The effects of these hormones on pulp and gingival cells were compared; addition of PTH, PGE2, and dibutyryl cAMP had no effect on gingival cell GAG synthesis, whereas their addition induced significant increases of GAG in pulp cells. These results indicate that PTH and PGE2 are involved in the differentiation of dental pulp cells and that these effects are mediated by cAMP.

In vitro effects of insulin on macromolecular events in newt limb regeneration blastemata

This work provides data demonstrating a stimulatory effect of insulin on macromolecular events occurring in cultured regeneration blastemata and demonstrates a synergistic interdependence between nerves and insulin in newt limb regeneration. The current experiments provide evidence for the following: (1) Insulin is paramount for expression of the mitogenic effect of nerves on cultures blastemata. (2) Insulin stimulates the incorporation of (3H)uridine into the acid-insoluble fraction of blastemal homogenates, but it does not alter the turnover rate of incorporated labeled uridine. (3) Insulin also stimulates the incorporation of 35SO4 and (3H)leucine into both chondroitinase-sensitive and chondroitinase-resistant blastemal proteoglycans. (4) Insulin increases the uptake of radiolabeled precursors by the blastemata, namely, (3H)leucine, (3H)uridine, 35SO4, (3H)alpha-aminoisobutyrate, and (3H)2-deoxy-D-glucose. The importance of insulin in the regulation of newt limb regeneration is discussed.

Chondrocyte metabolism as affected by vitamin A

Chondrocytes from 13-day-old embryonic chick sterna were cultured for 6 days in the presence of vitamin A (10 I.U./ml). Vitamin A treated chondrocytes became flattened and stellate within the first 24 hours of culture. After 6 days of culture, the treated cells contained 59% less DNA than the untreated controls. Sulfated glycosaminoglycan synthesis was inhibited 84%, and a greater percentage of GAG was secreted into the medium (90%) than in control cultures (78%). Vitamin A inhibited cell proliferation, and to varying degrees, RNA and protein synthesis, and these effects are dose dependent.