Recovery of stem cell proliferation by low intensity vibration under simulated microgravity requires LINC complex

Abstract

Mesenchymal stem cells (MSC) rely on their ability to integrate physical and spatial signals at load bearing sites to replace and renew musculoskeletal tissues. Designed to mimic unloading experienced during spaceflight, preclinical unloading and simulated microgravity models show that alteration of gravitational loading limits proliferative activity of stem cells. Emerging evidence indicates that this loss of proliferation may be linked to loss of cellular cytoskeleton and contractility. Low intensity vibration (LIV) is an exercise mimetic that promotes proliferation and differentiation of MSCs by enhancing cell structure. Here, we asked whether application of LIV could restore the reduced proliferative capacity seen in MSCs that are subjected to simulated microgravity. We found that simulated microgravity (sMG) decreased cell proliferation and simultaneously compromised cell structure. These changes included increased nuclear height, disorganized apical F-actin structure, reduced expression, and protein levels of nuclear lamina elements LaminA/C LaminB1 as well as linker of nucleoskeleton and cytoskeleton (LINC) complex elements Sun-2 and Nesprin-2. Application of LIV restored cell proliferation and nuclear proteins LaminA/C and Sun-2. An intact LINC function was required for LIV effect; disabling LINC functionality via co-depletion of Sun-1, and Sun-2 prevented rescue of cell proliferation by LIV. Our findings show that sMG alters nuclear structure and leads to decreased cell proliferation, but does not diminish LINC complex mediated mechanosensitivity, suggesting LIV as a potential candidate to combat sMG-induced proliferation loss.

Low Intensity Vibrations Augment Mesenchymal Stem Cell Proliferation and Differentiation Capacity during in vitro Expansion

“…2a). We recently reported that decreased cell proliferation under simulated microgravity results in decreased levels of RanGAP1 (Ran GTPase activating protein 1), RANG (Ran-specific GTPase-activating protein) and CDK1 (Cyclin-dependent kinase 1) proteins 27 . We have further reported increased RanGAP1 and RANG levels when LIV was used to rescue simulated microgravity-induced proliferation loss.…”

“…Application of LIV. Vibrations were applied at room temperature using methods we previously established 23,27 . Briefly, LIV was applied twice for 20 min separated by a 2 h rest period.…”

“…To understand what preserved proliferative ability means for MSC fate, we quantified the osteogenic and the adipogenic capacity of EP, EP + LIV, LP and LP + LIV groups. We have previously established the multipotentiality of MSCs at EP timepoints 23,27,[34][35][36][37][38][39] . In order to check the potential changes in basal mRNA expression at LP Figure 1.…”

“…Concomitant to changes in cellular structure, LIV activates nuclear effectors such as βcatenin and its subsequent accumulation in the nucleus 26 . Functionally, these changes lead to the improvement of osteogenic and proliferative capacity in MSCs 24,27 .…”

Factors implicating the validity and interpretation of mechanobiology studies in simulated microgravity environments

“…[12][13][14] Coupled with the sheer variability between systems, treating system conditions as a "black box" has led to contradictory findings within the growing body of simulated microgravity research. For example, s-μg culture is reported to induce apoptosis, [15][16][17][18][19] reduce endothelial cell migration, 20 inhibit stem cell differentiation [21][22][23] and proliferation, 24,25 as well as suppress metastasis 26,27 for certain cancer cell lines. Yet in other studies, s-μg culture is reported to reduce apoptosis, 28,29 enhance stem cell proliferation and differentiation potential, [30][31][32] increase endothelial cell migration, 33 promote cancer cell metastasis 34 or yielded a combination of increased stem cell proliferation and reduced differentiation potential.…”