Multiscale simulation of intervertebral disc multiphysics adaptations and protein turnover in astronauts

Abstract

During spaceflight, many astronauts experience moderate to severe lumbar pain, which might originate from intervertebral disc (IVD) swelling triggered by the lack of compressive loads in microgravity. IVD swelling alters nutrition diffusion in the largely avascular IVD, thereby affecting cell activity. However, to date, it is still unclear how unloading due to microgravity affects IVD multiphysics and consequent protein turnover. To shed light on this topic, a multiscale approach was used. Finite Element (FE) simulations with an L4-L5 mechanotransport IVD model simulated mechanically coupled nutrient diffusion in a normal gravitational environment and during five days and six months of space flight. Mechanotransport simulations provided local changes in pressure and nutrient concentrations within the IVD. Such information was subsequently used to feed an Agent-Based (AB) model that simulated a 1mm3

volume of 4000 cells in the central tissue of the IVD: the Nucleus Pulposus. The AB model allowed to assess the cell activity regarding tissue structural protein and protease mRNA expressions. Results suggest that astronaut’s IVD reach a stable prolonged swelling phase early on in the adaptation process to space, which leads to a series of biomechanical reactions that indicate signs of disc degeneration.