Effects of Simulated Microgravity on the Internalization of Cerium Oxide Nanoparticles by Proliferating Human Skeletal Myoblasts

Spaceflight typically exerts detrimental effects on living organisms by promoting/accelerating some degenerative processes associated with aging and pathology onset on Earth, like muscle degeneration. As possible countermeasures to spaceflight effects, a few recent studies successfully tested the administration of nanomaterials for tuning of cellular activities and for promotion of certain cell phenotypes in microgravity, but largely missed investigation of early interactions of these nanomaterials with their cellular targets under altered gravity conditions. This study aims at filling this gap by elucidation of early interactions of a selected typology of redox-active nanoparticles (cerium oxide nanoparticles, also termed nanoceria, NC) with proliferating human skeletal myoblasts (HSkM) by concomitant exposure to simulated microgravity (achieved by a random positioning machine, RPM). To this purpose, NC were synthesized by a direct precipitation method and were chemically, structurally, and functionally characterized by several independent techniques prior to administration to skeletal muscle cell cultures and loading on the RPM. Confocal and electron microscopy evidence of nanoparticle internalization by several mechanisms (mostly involving macropinocytosis) in HSkM is provided, along with evidence of transcriptional regulation of key antioxidant response markers (Nos1, Sod2, and Sod3), promising oxidative stress alleviation and muscle protection under mechanical unloading conditions.