C - Michigan Technological University

Chapter Four — Attempts to find an anti-apoptoticenvironment in hibernating bear serum remain inconclusive4.1 IntroductionOsteocyte apoptosis precedes bone loss in unloaded mice, and attenuatingosteocyte and osteoblast apoptosis with injections of PTH suppresses this bone loss[48-51, 56]. It is possible that osteocyte and osteoblast apoptosis are required fordisuse-induced bone loss, though no known studies have directly proven this idea.However, a study with a pan-caspase inhibitor in ovariectomized mice demonstrates thatcaspase activation is required for bone loss in that model of osteoporosis [162].Apoptosis-inducing threats (e.g. ischemia, metabolic acidosis, anorexia) are prevalent inhibernating animals, yet qualitative observations suggest that these animals resist largescaleapoptosis during hibernation (for review see: [163]). There are few in-depth studieson the apoptotic response during hibernation, though one study demonstrates reducedcaspase-3 activation and no change in DNA laddering in the gut of hibernating groundsquirrels compared to non-hibernating squirrels [45]. Bears may attenuate bone lossduring hibernation by reducing susceptibility of osteoblasts and osteocytes to apoptosis,possibly through the circulation of anti-apoptotic hormones. The purpose of this chapterand the next is to determine whether serum levels of anti-apoptotic hormones increaseduring hibernation, thus providing an anti-apoptotic environment for osteoblasts andosteocytes. In this study, serum levels of the osteoblast apoptosis regulators PTH,melatonin, and testosterone were quantified in the serum of hibernating and activeAmerican black bears. The hypothesis was that levels of the anti-apoptotic hormonesPTH and melatonin would increase, and the levels of the pro-apoptotic hormonetestosterone would decrease in serum of hibernating bears.4.2 Methods and materialsA total of 6 female black bears were captured and held in pens in the VirginiaTech Center for Bear Research from fall through spring, between the years 2006 and64