Simulated Microgravity Affects Numb Localization in Human Adipose-Derived Stem Cells

Abstract

An ultimate goal of human space exploration is to travel to Mars and beyond in search of scientific knowledge. However, a current problem in space exploration is that astronauts tend to develop osteoporosis or loss of bone mass. To recover bone mass, some tissue engineering applications use adult stem cells. Adult stem cells are known to asymmetrically divide into specialized cells like bone, muscles, cartilage, etc. However, our own results indicated that stem-cells exposed to simulated microgravity did not differentiate into specialized cells. It is not known why stem cells demonstrated inhibited differentiation on microgravity. We decided to study Numb, a cell fate determinant protein involved in osteogenesis. Numb promotes differentiation by inhibiting the Notch signaling pathway through localization changes in asymmetric stem cell division. We hypothesized that Numb localization is affected under microgravity. We approached this by plating human adipose-derived stem cells under standard gravity and simulated microgravity. We used our own ground-based simulated microgravity device based on lab-on-a-chip and clinorotation technology, as previously published. Cells were stained using immunofluorescence for intracellular Numb and imaged in a fluorescence microscope. Our results showed highly localized Numb in elongated cells in standard gravity. In contrast, Numb was not specifically localized for cells in microgravity independently of morphology. Our next step was to explore how to control Numb localization to increase differentiation. We used a micropattern method that allowed us to force the cells to take on specific shapes like squares, triangles, and circles. By controlling cell-substrate adhesion, we found that we were able to increase Numb localization. The potential applications of adult stem cells in microgravity may be inhibited due to the lack of numb localization, but we have shown that this can be reversed using techniques such as micropatterning.