The Effects of Simulated and Real Microgravity on Vascular Smooth Muscle Cells

Abstract

As considerations are being made for the limitations and safety of long-term human spaceflight, the vasculature is important given its connection to and impact on numerous organ systems. As a major constituent of blood vessels, vascular smooth muscle cells are of interest due to their influence over vascular tone and function. Additionally, vascular smooth muscle cells are responsive to pressure and flow changes. Therefore, alterations in these parameters under conditions of microgravity can be functionally disruptive. As such, here we review and discuss the existing literature that assesses the effects of microgravity, both actual and simulated, on smooth muscle cells. This includes the various methods for achieving or simulating microgravity, the animal models or cells used, and the various durations of microgravity assessed. We also discuss the various reported findings in the field, which include changes to cell proliferation, gene expression and phenotypic shifts, and renin-angiotensin-aldosterone system (RAAS), nitric oxide synthase (NOS), and Ca²⁺ signaling. Additionally, we briefly summarize the literature on smooth muscle tissue engineering in microgravity as well as considerations of radiation as another key component of spaceflight to contextualize spaceflight experiments, which by their nature include radiation exposure. Finally, we provide general recommendations based on the existing literature's focus and limitations.

Keywords: radiation; simulated microgravity; smooth muscle cell; spaceflight; tissue engineering.

Figure 1.

Experimental methods used to simulate microgravity. [A] Synthecon Rotating Wall Vessel (RWV) bioreactor. [B] SMCs on microcarrier beads in preparation for use in the RWV. [C] Gravite 3D clinostat. [D] Yuri/Airbus RPM with two independently driven perpendicular frames. [E] Illustration of hindlimb unloading for rodents; made with BioRender.

Figure 2.

Illustration of an artery in cross-section, and its constituent layers and components. Made with BioRender.

Figure 3.

Illustration of microgravity control conditions. [A-C] Comparison of three normal gravity controls to assess the full range of conditions relevant to comparison with simulated microgravity culture. [D] Conditions of an experimental sample in simulated microgravity. Actual spaceflight culture does not have equivalent fluid convection to benchtop reactors. Adapted from Poon 2020.

Figure 4.

(A) Phase contrast of coculture of EA.hy926 HUVEC-like cells, vascular smooth muscle cells, and fibroblasts at 21 days of RPM simulated microgravity (phase-contrast). (B, C) Sirius Red staining of cocultures of EA.hy926 HUVEC-like cells, vascular smooth muscle cells, and fibroblasts at 21 days of RPM simulated microgravity. Adapted from Grimm et al. (2014).

Figure 5.

Scheme of P2 Receptor Alteration and the Postulated Paracrine Effect in ECs and SMCs under Simulated Microgravity. Expression levels of several P2 receptor were altered in ECs and SMCs under 24 h clinostat-simulated microgravity. P2X7 and P2Y2 expression was differentially altered between ECs and SMCs under simulated microgravity. The change in P2X7 expression in ECs was compensated under SMC-conditioned medium and vice versa. Adapted from Zhang et al. 2014.