Microfluidic 3D Model of Heterochronic Parabiosis to Study Systemic Regulation of Skeletal Muscle Aging

Abstract

Muscle satellite cells (MuSCs) play an indispensable role in skeletal muscle regeneration after injury. However, their regenerative capacity declines with aging. Intriguingly, studies using parabiosis, a surgical technique that attaches two animals to share blood circulation, demonstrated that circulating factors from young animals can rejuvenate the regenerative capacity of aged animals. However, the exact identity of these putative youthful factors has yet to be elucidated. Due to the complexity of in vivo parabiosis, reliable identification of systemic rejuvenation factors remains a major hurdle. To overcome this challenge, we employed microengineering technologies and developed a 3D microfluidic circuit with biophysical and biochemical properties similar to in vivo muscle microenvironment. Here, we present a 3D micro‐vascularized muscle‐on‐a‐chip (VMoC) that exhibits key characteristics of the native MuSC niche, where FACS purified quiescent MuSCs are cultured in between myofibers and 3D hydrogel (extracellular matrix mimetic) underneath vascular endothelial cells. With the VMoC, we further integrated it to model parabiosis by co‐culturing cells/sera from young and aged animals. By adding the serum from young, aged, and Sod1−/− (oxidative stress model) mice to VMoCs, we demonstrate distinct myogenic activities of young MuSCs; VMoCs with aged and Sod1−/− sera showed significantly reduced myogenesis as measured by fusion index. Next, we replicated heterochronic parabiosis using our integrated chip‐to‐chip platform to assess the rejuvenating effects of young serum/cells. Interestingly, similar to in vivo parabiosis, when aged VMoCs were continuously exposed to the young systemic environment, the myogenic activity of aged MuSCs were significantly boosted. In addition, genes that regulate different steps of adult myogenesis (Desmin, MyoD, and Myogenin) were up‐regulated in the aged VMoC exposed to the young systemic environment. Furthermore, this rejuvenation effect in myogenesis was correlated with increased VEGF, which has been shown to play a crucial role in MuSC function in parabiosed VMoC. Collectively, our parabiosis‐on‐a‐chip platform will provide a state‐of‐the‐art pre‐clinical testing tool that will facilitate our understanding of the dynamic regulation of circulating humoral factors and potential drug discovery. More importantly, our approach can be translated into human clinical studies by replacing the murine cells with the corresponding human cells, emulating human parabiosis on‐a‐chip that blood transfusion cannot recapitulate.Support or Funding InformationNIH R21AR072287 (YJ), NIH R03AG062976 (YJ), and NIH DP2HL142050 (YK)