Bone Abstracts

Over the years, it has been demonstrated that the ability to maintain body core temperature in older adult’s declines with age. Temperature is a vital physical factor for cell growth and a downshift in core body temperature (<37 °C) might have a direct affect on maintaining bone density or repair fractures. Disruption in any of the cellular processes involved in bone remodelling leads to a net loss of bone mineral density and bone loss. Therefore our study looked at the changes in normal human osteoblast (NHOst) cell cytoskeleton, motility, and viability after short-term hypothermia. The expression of chaperone proteins, bone transcription factors and maturation proteins were also examined. NHOst cells were exposed to moderate (35 °C) and severe (27 °C) hypothermia and control (37 °C) at 1, 12, 24, and 72 h in a water-jacketed incubator. Changes in cell cytoskeleton were calculated based on fluorescence intensity. NHOst viability and motility was measured using MTS assay and CD44 ELISA respectively. Meanwhile, expression level of osteoblast transcription factors (Runx2 and osterix), cold (Rbm3), and heat shock (Hsp70) chaperone mRNA was quantitated using RT-PCR. Measurement of bone forming proteins; alkaline phosphatase (ALP), and osteocalcin (OCN) was done by ELISA. Hypothermic conditioning showed noticeable perturbation of the NHOst cytoskeleton compared to control. At 27 °C tubulin fibres were seen localized around the cell nucleus while actin was distributed throughout the cytoplasm. Increase in actin fluorescence intensity showed almost a similar trend in production of cell surface CD44 marker protein as both are involved in cell motility. Although cytoskeleton components were altered, NHOst remained metabolically viable at 35 °C. Response towards hypothermia constitutively enhanced expression of Rbm3 possibly to facilitate mRNA translation. Meanwhile, Runx2 and osterix were shown to co-regulate. Up-regulation of Runx2 induced osterix mRNA under 35 °C treatment indicating osteoblast differentiation was retained. Hypothermia increased ALP activity while OCN protein was expressed except at 72 h. Moderate hypothermia exerted an adaptive effect by retaining NHOst cell metabolism and bone function particularly at 12 h. We speculate that decline in core body temperature is not the reason for bone loss seen in elderly since it appears to stimulate bone mineralization.