Vasdev, Amrit K.

Neurotrophic signaling is essential to the maintenance of diaphragm muscle function across the lifespan. With aging, there is an age‐related loss of neurotrophic signaling and a resultant increase in diaphragm muscle denervation and impairment in neuromuscular transmission. We hypothesized that enhancing neurotrophic signaling via the tropomyosin‐related kinase receptor subtype B (TrkB) using the small molecule TrkB agonist 7,8‐dihydroxyflavone (7,8‐DHF) would mitigate age‐related changes in diaphragm neuromuscular transmission and possibly sarcopenia (muscle atrophy and force loss). Adult male TrkB F616A mice (n=32) were randomized to receive 6‐month oral treatment with vehicle (control), 7,8‐DHF, or co‐treatment with 7,8‐DHF and 1NMPP1(a specific inhibitor of TrkB kinase activity in TrkB F616A mice) beginning at 18 and ending at 24 months of age. Mice were analyzed for neuromuscular transmission failure using diaphragm muscle‐phrenic nerve preparations, diaphragm muscle force, and morphologic characteristics of sarcopenia. Chronic 7,8‐DHF treatment did not improve diaphragm neuromuscular function or force (P≥0.25). Co‐treatment with 7,8‐DHF and 1NMPP1 decreased the ratio of the initial nerve stimulation‐derived to initial muscle stimulation‐derived force (~22%) compared to vehicle (p=0.01), consistent with a deleterious effect of inhibiting TrkB kinase activity on aging diaphragm muscle. With age, there was fiber type specific atrophy of type IIa and type IIx and/or IIb diaphragm muscle fibers. There was no evidence of a protective effect of 7,8‐DHF on muscle fiber cross‐sectional area. Taken together, these results support a role for BDNF/TrkB signaling in old age but do not support 7,8‐DHF as a therapeutic agent to mitigate age‐related effects on diaphragm muscle function. Support or Funding Information Supported by R01‐AG044615, T32‐HL105355, and the Mayo Clinic.

Sarcopenia is the age‐related decline of skeletal muscle function. Sarcopenia involves loss of motor neurons and the subsequent denervation of muscle fibers. Denervated muscle fibers can be re‐innervated through terminal axonal sprouting of neighboring axons. Given the predominant role of motor neurons in establishing muscle fiber type, we hypothesized that sarcopenia (and the associated partial denervatin effects) result in clustering of muscle fibers of the same type (classified by myosin heavy chain isoform composition). Fiber type specific immunofluorescence histology was used to quantify fiber clustering in murine diaphragm muscle (n=15) at 6 and 24 months of age. Clustering was analyzed using the distance between fibers of the same fiber type as well as quantification of the number of type‐identified fibers in a cluster. There was a 14% decrease to the closest fiber for type I and a 24% increase for type IIx and/or IIb fibers (P<0.001) in old vs. young mice. Additionally, a 34% increase to the 3 closest type IIx and/or IIb fibers was found (P<0.001). Changes in the interfiber distances for type‐identified fibers reveals important effects that consider changes in fiber size and proportion across disease conditions. This novel method of analyzing fiber type clustering may be useful in examining pathophysiological conditions of motor unit loss in neuromuscular disorders, myopathies, dystrophies, injuries, or amyotrophic lateral sclerosis. Supported by R01‐AG044615, T32‐HL105355, and the Mayo Clinic.

Introduction There is a considerable implementation gap in managing early stage chronic kidney disease (CKD) in primary care despite the high prevalence and risk for increased morbidity and mortality associated with CKD. This systematic review aims to synthesise the evidence of efficacy of implementation interventions aimed at primary care practitioners (PCPs) to improve CKD identification and management. We further aim to describe the interventions’ behavioural change components. Methods and analysis We will conduct a systematic review of studies from 2000 to October 2017 that evaluate implementation interventions targeting PCPs and which include at least one clinically meaningful CKD outcome. We will search several electronic data bases and conduct reference mining of related systematic reviews and publications. An interdisciplinary team will independently and in duplicate, screen publications, extract data and assess the risk of bias. Clinical outcomes will include all clinically meaningful medical management outcomes relevant to CKD management in primary care such as blood pressure, chronic heart disease and diabetes target achievements. Quantitative evidence synthesis will be performed, where possible. Planned subgroup analyses include by (1) study design, (2) length of follow-up, (3) type of intervention, (4) type of implementation strategy, (5) whether a behavioural or implementation theory was used to guide study, (6) baseline CKD severity, (7) patient minority status, (8) study location and (9) academic setting or not. Ethics and dissemination Approval by research ethics board is not required since the review will only include published and publicly accessible data. Review findings will inform a future trial of an intervention to promote uptake of CKD diagnosis and treatment guidelines in our primary care setting and the development of complementary tools to support its successful adoption and implementation. We will publish our findings in a peer-reviewed journal and develop accessible summaries of the results. PROSPERO registration number CRD42018102441.