Primary human bone cultures from older patients do not respond at continuum levels of in vivo strain magnitudes.
Osteoporosis is characterized by excessive loss of bone mass, while exercise is believed to maintain or enhance bone mass. Since exercise marginally affects osteoporosis, we wondered whether bone cells from osteoporotic patients would fail to respond to strain. Primary human bone-like cultures were obtained from females over age 60 with hip arthroplasty procedures performed for either osteoporotic fracture (n = 8) or non-osteoporotic osteoarthrosis (n = 5). Cultures (96,000 cell/cm2) were strained in rectangular optically clear silastic wells. Three periods of uniaxial substratum strain (1000 micro-strain, 1 Hz, 10,000 cycles, sine wave) were provided every 24 h using a four-point bending, computer-controlled device. Results at a frequency of 1 Hz were compared to cultures exposed to 20 Hz with bone cells derived from one osteoarthritic subject. Alterations in protein level expression of bone-related proteins were determined using a semi-quantitative confocal approach along with enzyme (alkaline phosphatase) activity and enzyme mRNA copy number using cRNA RT-PCR. Strain did not alter levels of bone-related protein levels, enzyme activity, or steady state copy number per cell in response to strain in either group. Strained cultures from osteoporotic patients exhibited little variation from unstrained controls, while individual cultures from osteoarthritic patients exhibited increases in one protein or the other. The results suggest that bone cells from older individuals may not be responsive to continuum levels of strain anticipated with vigorous activity.