Administration frequency as well as dosage of PTH are associated with development of cortical porosity in ovariectomized rats

To investigate whether the administration frequency of parathyroid hormone(PTH) is associated with the development of cortical porosity, this study established 15 dosage regimens of teriparatide [human PTH(1–34), TPTD] with four distinct concentrations and four distinct administration frequencies of TPTD to 16-week-old ovariectomized rats. Our analyses demonstrated that the bone mineral density, mechanical properties, and bone turnover were associated with the total amount of TPTD administered. Our observations further revealed that the cortical porosity was markedly developed as a result of an increased administration frequency with a lower concentration of total TPTD administration in our setting, although the highest concentration also induced cortical porosity. Deconvolution fluorescence tiling imaging on calcein-labeled undecalcified bone sections also demonstrated the development of cortical porosity to be closely associated with the bone site where periosteal bone formation took place. This site-specific cortical porosity involved intracortical bone resorption and an increased number and proximity of osteocytic lacunae,occasionally causing fused lacunae. Taken together, these findings suggested the involvement of local distinctions in the rate of bone growth that may be related to the site-specific mechanical properties in the development of cortical porosity induced by frequent and/or high doses of TPTD.

Heterologous Expression of Thermolabile Proteins Enhances Thermotolerance in Escherichia coli

Heat shock proteins (HSPs) play important roles in the mechanism of cellular protection against various environmental stresses. It is well known that accumulation of misfolded proteins in a cell triggers the HSPs expression in prokaryotes as well as eukaryotes. In this study, we heterologously expressed two proteins in E. coli, namely, citrate synthase (CpCSY) and malate dehydrogenase (CpMDH) from a psychrophilic bacterium Colwellia psychrerythraea 34H (optimal growth temperature 8°C). Our analyses using circular dichromism along with temperature-dependant enzyme activities measured in purified or direct cell extracts confirmed that the CpCSY and CpMDH are thermolabile and present in misfolded form even at physiological growth temperature. We observed that the cellular levels of HSPs, both GroEL and DnaK cheperonins were increased. Similarly, higher levels were observed for sigma factor s32 which is specific to heat-shock protein expression. These results suggest that the misfolded-thermolabile proteins expressed in E. coli induced the heat shock response. Furthermore, heat treatment (53°C) to wild type E. coli noticeably delayed their growth recovery but cells expressing CpCSY and CpMDH recovered their growth much faster than that of wild type E. coli. This reveals that the HSPs expressed in response to misfolded-thermolabile proteins protected E. coli against heat-induced damage. This novel approach may be a useful tool for investigating stress-tolerance mechanisms of E. coli.