Microgravity Potentiates Stem Cell Proliferation While Sustaining the Capability of Differentiation

TLDR

A 3‑D clinostat simulating microgravity (≈10⁻³ G) was used to culture hMSCs, and the resulting cells were then implanted into cartilage‑defective mice to assess differentiation. Under simulated microgravity, hMSCs expanded 13‑fold, maintained stem‑cell marker expression and telomere length, and differentiated into hyaline cartilage in vivo, whereas 1‑G cultured cells lost these properties.

Abstract

A three-dimensional (3D) clinostat is a device for generating multidirectional G force, resulting in an environment with an average of 10−3 G. Here we report that human mesenchymal stem cells (hMSCs) cultured in a 3D-clinostat (group CL) showed marked proliferation (13-fold in a week) compared with cells cultured under normal conditions of 1 G (group C) (4-fold in a week). Flow cytometry revealed a 6-fold increase in the number of hMSCs double-positive for CD44/CD29 or CD90/CD29 in group CL after 7 days in culture, compared with group C. Telomere length remained the same in cells from both groups during culturing. Group C cells showed increasing expression levels of type II collagen and aggrecan over the culture period, whereas group CL cells showed a decrease to undetectable levels. Pellets of hMSCs from each group were explanted into cartilage-defective mice. The transplants from group CL formed hyaline cartilage after 7 days, whereas the transplants from group C formed only noncartilage tissue containing a small number of cells. These results show that hMSCs cultured in a 3D-clinostat possess the strong proliferative characteristic of stem cells and retain their ability to differentiate into hyaline cartilage after transplantation. On the contrary, cells cultured in a 1-G environment do not maintain these features. Simulated microgravity may thus provide an environment to successfully expand stem cell populations in vitro without culture supplements that can adversely affect stem cell-derived transplantations. This method has significant potential for regenerative medicine and developmental biology.