C - Michigan Technological University

stimulated in filtered 2% FBS (p=0.0071) (Figure 5.8 A). The cells grown for 6 hours infiltered 2% bear serum were not significantly different between prehibernation andhibernation seasons (p=0.4490) (Figure 5.8 B).Serum levels of BSALP and adiponectin were positively correlated, and NPY wasinversely correlated, with the caspase-3/7 response of cultured osteoblasts to apoptoticthreat (Table 5.4). The gene expression of osteoblast differentiation markers OCN andRunx2 increased in differentiating osteoblasts cultured in serum from post-hibernationbears, compared to those in serum from prehibernation and hibernation bears (Table5.2).5.4 DiscussionHibernating bears have a unique ability to maintain bone mechanical strengthand structural properties despite extended periods of disuse [16-21, 173, 174]. Thepurpose of this study was to explore the hypothesis that a serum-borne factor inhibernating bears suppresses osteoblast apoptosis. Such a suppression of apoptosismay prevent disuse-induced bone loss during hibernation. MC3T3-E1 osteoblast-likecells were cultured in serum from active and hibernating bears for 24 hours, followed byan apoptotic threat. Figure 5.2 demonstrates a reduction in caspase-3 and -7 activationin cells cultured in hibernating bear serum, supporting the hypothesis. These data alsodemonstrate an increased caspase-3/7 response in post-hibernation serum compared toprehibernation serum (Table 5.2), indicating the metabolic rate of bone may beincreased in the weeks immediately following hibernation. This higher metabolism inbone was also indicated in the gene expression data (Table 5.2). Expression of OCNand Runx2, markers of osteoblast differentiation, were significantly higher in osteoblastscultured in post-hibernation serum. Such an increased metabolic state in the bones ofpost-hibernation bears has been indicated in previous publications [35].The next step was to demonstrate that apoptosis decreases in the bone tissue ofhibernating bears, compared to active bears. This step has proven more difficult.Hibernating animals are exposed to many conditions that would cause extensive tissuedamage due to apoptosis in other animals; however, they fully recover from annual78