Parathyroid hormone inhibits collagen synthesis and the activity of rat Col1a1 transgenes mainly by a cAMP-mediated pathway in mouse calvariae

Abstract

We examined the effect of parathyroid hormone and various signaling molecules on collagen synthesis and chloramphenicol acetyltransferase activity in cultured transgenic mouse calvariae carrying fusion genes of the rat Col1a1 promoter and the chloramphenicol acetyltransferase reporter. After 48 h of culture, parathyroid hormone, forskolin, dibutyryl cAMP, 8-bromo cAMP, and phorbol myristate acetate inhibited transgene activity, while the calcium ionophore ionomycin had no effect. Pretreatment of calvariae with the phosphodiesterase inhibitor isobutylmethylxanthine potentiated the inhibitory effect of 1 nM parathyroid hormone on transgene activity and collagen synthesis. Parathyroid hormone further inhibited transgene activity and collagen synthesis in the presence of phorbol myristate acetate. Parathyroid hormone inhibition of transgene activity and collagen synthesis was not affected by indomethacin or interleukin-6. After 48 h of culture, parathyroid hormone inhibited chloramphenicol acetyltransferase activity by 50-85% in cultured calvariae carrying transgenes having progressive 5' upstream deletions of promoter DNA down to -1683 bp. These data show that the inhibitory effect of parathyroid hormone on Col1a1 expression in mouse calvariae is mediated mainly by the cAMP signaling pathway. Prostaglandins and IL-6 are not local mediators of the parathyroid hormone response in this model. Finally, regions of the Col1a1 promoter downstream of -1683 bp are sufficient for parathyroid hormone inhibition of the Col1a1 promoter.

Vitamin D Regulation of Type I Collagen Expression in Bone

“…It has been suggested that some biological effects of 1,25(OH) 2 D 3 may be mediated by the protein kinase C (PKC) signaling pathway [74]. We have shown that stimulation of PKC with phorbol myristate acetate inhibits collagen synthesis in fetal rat calvariae [96] and ColCAT3.6 expression in transgenic mouse calvariae [97]. Therefore, 1,25(OH) 2 D 3 activation of the PKC pathway might inhibit Col1a1 expression.…”

Type I diabetic bone phenotype is location but not gender dependent

“…Because the response in calvaria is similar to tibia and femur, the calvaria can be used for analyses examining mechanism of diabetes induced bone loss. This Wnding also supports the multiple reports utilizing calvaria and calvaria derived osteoblasts to examine mechanisms of bone responsiveness to factors such as hormones, stress, and healing (Aronow et al 1990;Bogdanovic et al 2000;Harrison et al 1998;Ikegame et al 2001;Jiang et al 2006;Kream et al 1985;McCauley et al 2001;Woitge and Kream 2000).…”

Differential Regulation of Osteoblast Activity by Th Cell Subsets Mediated by Parathyroid Hormone and IFN-γ

“…In contrast, type I collagen and osteonectin genes were well expressed. Although consistent with an earlier study (53), PTH 1-34 treatment alone appeared to moderately inhibit the expression of type I collagen, and Th2 cell condition medium did not exert a strong effect on type I collagen gene expression whether or not PTH was antagonized by PTH (Fig. 7A).…”