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BACKGROUNDInjuries from falls are major contributors to complications and death in older adults. Despite evidence from efficacy trials that many falls can be prevented, rates of falls resulting in injury have not declined. METHODSWe conducted a pragmatic, cluster-randomized trial to evaluate the effectiveness of a multifactorial intervention that included risk assessment and individualized plans, administered by specially trained nurses, to prevent fall injuries. A total of 86 primary care practices across 10 health care systems were randomly assigned to the intervention or to enhanced usual care (the control) (43 practices each). The participants were community-dwelling adults, 70 years of age or older, who were at increased risk for fall injuries. The primary outcome, assessed in a time-to-event analysis, was the first serious fall injury, adjudicated with the use of participant report, electronic health records, and claims data. We hypothesized that the event rate would be lower by 20% in the intervention group than in the control group. RESULTSThe demographic and baseline characteristics of the participants were similar in the intervention group (2802 participants) and the control group (2649 participants); the mean age was 80 years, and 62.0% of the participants were women. The rate of a first adjudicated serious fall injury did not differ significantly between the groups, as assessed in a time-to-first-event analysis (events per 100 person-years of follow-up, 4.9 in the intervention group and 5.3 in the control group; hazard ratio, 0.92; 95% confidence interval [CI], 0.80 to 1.06; P = 0.25). The rate of a first participant-reported fall injury was 25.6 events per 100 person-years of follow-up in the intervention group and 28.6 events per 100 person-years of follow-up in the control group (hazard ratio, 0.90; 95% CI, 0.83 to 0.99; P = 0.004). The rates of hospitalization or death were similar in the two groups. CONCLUSIONSA multifactorial intervention, administered by nurses, did not result in a significantly lower rate of a first adjudicated serious fall injury than enhanced usual care.

The findings of the STRIDE study will have important clinical and policy implications for the prevention of fall injuries in older adults.

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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.

Mitochondrial dysfunction, chronic inflammation and muscle aging are closely linked. Mitochondrial clearance is a process to dampen inflammation and is a critical pre-requisite to mitobiogenesis. The combined effect of aging and chronic inflammation on mitochondrial degradation by autophagy is understudied. In interleukin 10 null mouse (IL-10tm/tm), a rodent model of chronic inflammation, we studied the effects of aging and inflammation on mitochondrial clearance. We show that aging in IL-10tm/tm is associated with reduced skeletal muscle mitochondrial death signaling and altered formation of autophagosomes, compared to age-matched C57BL/6 controls. Moreover, skeletal muscles of old IL-10tm/tm mice have the highest levels of damaged mitochondria with disrupted mitochondrial ultrastructure and autophagosomes compared to all other groups. These observations highlight the interface between chronic inflammation and aging on altered mitochondrial biology in skeletal muscles.

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Background The role of Numb, a protein that is important for cell fate and development and that, in human muscle, is expressed at reduced levels with advanced age, was investigated; adult mice skeletal muscle and its localization and function within myofibres were determined. Methods Numb expression was evaluated by western blot. Numb localization was determined by confocal microscopy. The effects of conditional knock out (cKO) of Numb and the closely related gene Numb‐like in skeletal muscle fibres were evaluated by in situ physiology, transmission and focused ion beam scanning electron microscopy, three‐dimensional reconstruction of mitochondria, lipidomics, and bulk RNA sequencing. Additional studies using primary mouse myotubes investigated the effects of Numb knockdown on cell fusion, mitochondrial function, and calcium transients. Results Numb protein expression was reduced by ~70% (P < 0.01) at 24 as compared with 3 months of age in gastrocnemius and tibialis anterior muscle. Numb was localized within muscle fibres as bands traversing fibres at regularly spaced intervals in close proximity to dihydropyridine receptors. The cKO of Numb and Numb‐like reduced specific tetanic force by 36% (P < 0.01), altered mitochondrial spatial relationships to sarcomeric structures, increased Z‐line spacing by 30% (P < 0.0001), perturbed sarcoplasmic reticulum organization and reduced mitochondrial volume by over 80% (P < 0.01). Only six genes were differentially expressed in cKO mice: Itga4, Sema7a, Irgm2, Vezf1, Mib1, and Tmem132a. Several lipid mediators derived from polyunsaturated fatty acids through lipoxygenases were up‐regulated in Numb cKO skeletal muscle: 12‐HEPE was increased by ~250% (P < 0.05) and 17,18‐EpETE by ~240% (P < 0.05). In mouse primary myotubes, Numb knockdown reduced cell fusion (~20%, P < 0.01) and delayed the caffeine‐induced rise in cytosolic calcium concentrations by more than 100% (P < 0.01). Conclusions These findings implicate Numb as a critical factor in skeletal muscle structure and function and suggest that Numb is critical for calcium release. We therefore speculate that Numb plays critical roles in excitation–contraction coupling, one of the putative targets of aged skeletal muscles. These findings provide new insights into the molecular underpinnings of the loss of muscle function observed with sarcopenia.