Mechanical control of MSC adipogenesis does not require Lamin A/C

Mesenchymal stem cells (MSC) maintain the musculoskeletal system by differentiating into multiple cell types including osteocytes and adipocytes. Mechanical signals, including strain and low intensity vibration (LIV), are important regulators of MSC differentiation. Lamin A/C is a vital nucleoskeleton protein that provides mechanical properties to the nucleus and mechanical competency to MSCs. Loss of Lamin A/C has been associated with reduced structural integrity and genomic regulation of the nucleus, but direct involvement of Lamin A/C in mechanical regulation of MSC differentiation is unknown. We investigated the effects of Lamin A/C depletion on the nucleus and regulation of adipogenesis during mechanical stimulation. Upon Lamin A/C depletion, the nucleus experienced decreased area, height, volume, and stiffness while the focal adhesion phosphorylation in response to LIV and dynamic substrate strain remained intact. Cells experiencing Lamin A/C depletion undergo slower adipogenesis than control cells indicating a loss of genomic regulation due to the depletion of Lamin A/C. Mechanical stimulation via daily LIV application induced a reduction of adiponectin protein levels in both control and Lamin A/C depleted cells. RNA-seq data indicated a large adipogenic mRNA shift in control cells while Lamin A/C depleted cells showed a blunted adipogenic mRNA profile. Treatment with LIV did not induce large trascriptome changes in ether control or Lamin A/C depleted MSCs except for lowered intereferon response, suggested that LIV effects on adipogenesis may not occur at the transcriptional level. In summary, focal adhesion activation by dynamic mechanical signals and LINC complex elements largely remain unaltered under Lamin A/C depletion. While the adipogenic commitment was dependent upon Lamin A/C, the reduction of adiponectin protein in response to LIV was independent of Lamin A/C indicating that the Lamin A/C depletion and mechanical regulation of adipogenesis may not utilize similar pathways to elicit a response in MSCs. Investigation of LIV mechanical forces of adiogenic differentiation during Lamin A/C depletion. Sample groups are delineated via labeling of "S" followed by a number between 1-6. Such that samples labeled with "S1" are the first sample group and "S6" is the last. The first experimental group are samples labeled with "S1" and "S2". The second experimental group are the samples labeled with "S3" and "S4". The third experimental group's samples are labeled with "S5" and "S6". Samples labeled with "AP" are treated with only adiogeneic media. Samples labeled with "APLV" have both adipogeneic media and LIV mechanical force treatment. Samples labeled with "NAL" have neither adipogenic media nor LIV mechanical force treatment.