Anti-apoptotic signaling as a cytoprotective mechanism in mammalian hibernation

Abstract

In the context of normal cell turnover, apoptosis is a natural phenomenon involved in making essential life and death decisions. Apoptotic pathways balance signals which promote cell death (pro-apoptotic pathways) or counteract these signals (anti-apoptotic pathways). We proposed that changes in anti-apoptotic proteins would occur during mammalian hibernation to aid cell preservation during prolonged torpor under cellular conditions that are highly injurious to most mammals (e.g. low body temperatures, ischemia). Immunoblotting was used to analyze the expression of proteins associated with pro-survival in six tissues of thirteen-lined ground squirrels, Ictidomys tridecemlineatus. The brain showed a concerted response to torpor with significant increases in the levels of all anti-apoptotic targets analyzed (Bcl-2, Bcl-xL, BI-1, Mcl-1, cIAP1/2, xIAP) as well as enhanced phosphorylation of Bcl-2 at S70 and T56. Heart responded similarly with most anti-apoptotic proteins elevated significantly during torpor except for Bcl-xL and xIAP that decreased and Mcl-1 that was unaltered. In liver, BI-1 increased whereas cIAP1/2 decreased. In kidney, there was an increase in BI-1, cIAP and xIAP but decreases in Bcl-xL and p-Bcl-2(T56) content. In brown adipose tissue, protein levels of BI-1, cIAP1/2, and xIAP decreased significantly during torpor (compared with euthermia) whereas Bcl-2, Bcl-xL, Mcl-1 were unaltered; however, Bcl-2 showed enhanced phosphorylation at Thr56 but not at Ser70. In skeletal muscle, only xIAP levels changed significantly during torpor (an increase). The data show that anti-apoptotic pathways have organ-specific responses in hibernators with a prominent potential role in heart and brain where coordinated enhancement of anti-apoptotic proteins occurred in response to torpor.

Prevention of muscle wasting and osteoporosis: the value of examining novel animal models

“…Similar to aestivating frogs, studies of differential gene expression in arctic ground squirrels (Spermophilus parryii) found that the mRNA expression of genes involved in apoptosis increased significantly in skeletal muscle during interbout arousals (Yan et al, 2008). In skeletal muscle of ground squirrels, however, the protein expression of xIAP (aka BIRC4) increased significantly in torpid animals (Rouble et al, 2013) (Table 4). This indicates the possibility that IAP-mediated inhibition of caspase activity may be a critical regulatory mechanism which enhances survival of myocytes in dormant species that are resistant to disuse atrophy.…”

The involvement of mRNA processing factors TIA-1, TIAR, and PABP-1 during mammalian hibernation

“…Equal amounts from each sample were loaded onto 10-12 % SDS-polyacrylamide gels and run at 180 V for 45-60 min (except for TIA-1 p15 which was run on a 15 % Tris-Tricine gel) as previously described by Rouble et al (2013). Proteins were then transferred to polyvinylidene difluoride (PVDF) membrane (0.45 μm PVDF for SDS-PAGE, 0.2 μm PVDF for TrisTricine gels) by electroblotting at 160 mA for 1-1.5 h. Membranes were blocked with milk and made up in TBST (20 mM Tris base, pH 7.6, 140 mM NaCl, 0.05 % v/v Tween-20) to prevent nonspecific binding of antibodies.…”

Prioritization of skeletal muscle growth for emergence from hibernation

“…Several hypotheses have been advanced to explain retention of muscle mass in small mammals during winter, including: the preservation benefits of intermittent shivering activity (e.g. Nowell et al, 2011); a reduction in muscle degradation capacity at low temperature (Nagano et al, 2003;Velickovska et al, 2005); continued transcriptional activity in satellite cell nuclei throughout winter (Malatesta et al, 2009); and up-regulation of candidate muscle-preserving proteins (Lee et al, 2010;Nowell et al, 2011;Kornfeld et al, 2012;Rouble et al, 2013;Xu et al, 2013).…”