Multiscale Microgels Delivering GDNF and Agrin with Resistance Training to Enhance Outcomes in Sarcopenia - Project Summary Sarcopenia, the loss of muscle mass and strength, affects upwards of 30% of individuals ≥ 60 years of age. This causes many adverse effects, including increased risk of falls and fractures, impaired mobility, loss of independence, lower quality of life, health care demand, morbidity and mortality. Currently, there exists no therapeutic treatment available for sarcopenia patients, and the only available intervention is resistance training regimens. In order to further improve outcomes and to treat those individuals with co-morbidities who have limited ability for resistance training, new treatment paradigms are needed. In sarcopenia, the loss of motor neurons, axon retraction and denervation at neuromuscular junctions (NMJs), and changes in acetylcholine receptor (AChR) density interrupt the healthy neuromuscular signaling process. This project will test the ability of multiscale microgels, which release biologics that impact both pre- and post-synaptic NMJ sites, to improve outcomes in sarcopenia. Glial cell line derived neurotrophic factor (GDNF) and agrin will be loaded into porous silicon nanoparticles (pSiNPs). GDNF is a neurotrophin which has been shown to be a potent facilitator of motoneuron survival and NMJ formation, while agrin promotes AChR aggregation and maintenance of NMJ morphology on muscle fibers. pSiNPs act to sustain the activity of proteins trapped in their ~10 nm pores and increase the release time of biologics. The GDNF and agrin loaded-pSiNPs will then be incorporated into polyethylene glycol (PEG) microgels. These serve as injectable carriers that can interface with cells at the site of injection through their inherent microporosity and microscale surfaces. In Aim 1, we will verify the retention of protein activity through neuronal and myocyte in vitro assays. Multiscale microgels will be injected into both the soleus and the plantaris muscles of 24 month aged mice to distinguish how fast-twitch and slow-twitch muscles respond to our treatment paradigm. We will evaluate the pharmacokinetics of fluorescently labeled GDNF and agrin through muscle tissue sections. In Aim 2, we will test how our multiscale microgels compare to resistance training in sarcopenia by employing progressive weighted wheel running (PoWeR) in 24-month aged mice. Aim 2 will consist of 5 groups: 1) sedentary control, 2) sedentary control w/ control multiscale microgel, 3) PoWeR training, 4) GDNF/agrin combinatorial multiscale microgels, and 5) GDNF/agrin combinatorial multiscale microgels with PoWeR training. We will determine morphometric, histological, and functional outcomes. Single nucleus RNA-seq analysis will be used to determine how each treatment effects myofiber transcriptome with a particular focus of NMJ myonuclei. Upon completion of this work, we will have developed multiscale microgels that release GDNF and agrin for 1 month+, and determined their impact on NMJ morphology and muscle function. Future applications could use this platform to study different sarcopenia interventions, ranging from therapies targeted to pre-synaptic neurons to myocytes and satellite cells. Importantly, researchers can use our results to interpret the impact that the NMJ has on other neuromuscular disorders, including myasthenia gravis.
