Inflammation and mortality in a frail mouse model

Abstract

Mice homozygous for targeted deletion of the interleukin 10 gene (Il-10) have been partially characterized as a model for human frailty. These mice have increased serum interleukin (IL)-6 in midlife, skeletal muscle weakness, and an altered skeletal muscle gene expression profile compared to age and sex-matched C57BL/6 (B6) control mice. In order to further characterize for use as a frailty model, we evaluated the evolution of inflammatory pathway activation, endocrine change, and mortality in these mice. Serum was collected in groups of ageand sex-matched B6.129P2-Il10 tm1Cgn /J (IL-10 tm/tm ) mice and B6 control mice at age 12, 24, 48, 72, and 90 weeks. Cytokines including IL-6, interleukin 1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), chemokine (C-X-C motif) ligand 1 (KC), IL-12, and IL-10 were measured using electro-chemiluminescent multiplex immunoassay and insulin-like growth factor 1 (IGF-1) was measured using solid-phase enzyme-linked immunosorbent assay. A separate longitudinal cohort was monitored from age 35 weeks to approximately 100 weeks. Survival was evaluated by Kaplan-Meier survival estimates and detailed necropsy information was gathered in a subset of mice that died or were sacrificed. In IL-10 tm/tm mice compared to B6 controls, serum IL-6, IL-1β, TNF-α, IFN-γ, KC levels were significantly elevated across the age groups, serum mean IGF-1 levels were higher in the 48-week-old groups, and overall mortality rate was significantly higher. The quadratic relationship between IGF-1 and age was significantly different between the two strains of mice. Serum IL-6 was positively associated with IGF-1 but the effect was significantly larger in IL-10 tm/tm mice. These findings provide additional rationale for the use of the IL-10 tm/tm mouse as a model for frailty and for lowgrade inflammatory pathway activation.

Skeletal muscle ATP kinetics are impaired in frail mice

“…The IL10 tm/tm mice develop an age-related increase in SM weakness, inflammation and increased mortality compared to age-matched B6 mice and thus have been proposed as a model of human frailty (Walston et al 2008;Ko et al 2012). We report here, for the first time, that in vivo SM energy metabolism is deranged at rest in frail IL10 tm/tm mice as evidenced by a decline in intracellular [PCr], accumulation of P i , together with a decrease in the rate of ATP synthesis via CK (i.e., CK flux) and in the unidirectional rate of ATP synthesis from P i as compared to age-matched controls.…”

“…Elevated SM in vitro citrate synthase activity in IL10 tm/tm mice argues against a decline in mitochondrial content. Nonetheless, it is possible that mitochondrial enzymes were oxidatively modified (i.e., carbonylation or nitrotyrosine modification) (Feng et al 2008;Staunton et al 2011) owing to enhanced inflammation and oxidative stress in IL10 tm/tm mice (Ko et al 2012) which in turn could impair mitochondrial substrate oxidation and/or oxidative phosphorylation. Whatever the reason, the finding of substantially lower SM unidirectional P i →ATP synthesis rates in IL10 tm/tm mice (vs. control) is novel and not predicted by in vitro measures.…”

“…Ninety-two-week-old male IL-10 deficient (IL10 tm/tm ) and age-and sex-matched C57/BL6 (B6) mice were used for this study. Strength and activity decline with age in IL10 tm/tm mice, as compared to control mice, and mortality is increased at this age (Walston et al 2008;Ko et al 2012). IL10 tm/tm mice were homozygous for the IL10 tm/Cgn targeted mutation and were fully backcrossed on B6 background (Kuhn et al 1993).…”

“…Prior to introduction to the barrier, mice were quarantined for at least 1 month and tested to confirm SPF status. The barrier was sentinel tested for a number of pathogens as elaborated in detail previously (Ko et al 2012). Mice were housed in 75 in.…”

“…Despite recent advances in frailty research in human cohorts, the mechanisms that mediate SM decline and adverse outcomes in frailty remain unclear (Kanapuru and Ershler 2009). The homozygous interleukin-10 null, B6.129P2-IL10 ™/Cgn /J (IL10 ™/™ ) mouse has been proposed as a model to study the biology linking chronic inflammation and frailty (Walston et al 2008) given that they, like frail humans, develop elevated serum interleukin-6 (IL6), muscle weakness, and higher mortality compared to age-matched C57BL/6J (B6) controls (Walston et al 2008;Ko et al 2012).…”