Cross-linked matrix rigidity and soluble retinoids synergize in nuclear lamina regulation of stem cell differentiation

Synergistic cues from extracellular matrix and soluble factors are often obscure in differentiation. Here, the rigidity of crosslinked collagen synergizes with retinoids in the osteogenesis of human marrow mesenchymal stem cells (MSCs). Collagen nano-films serve as a model matrix that MSCs can easily deform unless the film is enzymatically crosslinked, which promotes the spreading of cells and the stiffening of nuclei as both actomyosin assembly and nucleoskeletal lamin-A increase. Expression of lamin-A is known to be controlled by Retinoic Acid Receptor (RAR) transcription factors, but rigid matrix is needed to induce rapid nuclear accumulation of the RARG isoform and subsequent expression of osteogenic markers. Rigid substrates such as culture plastic are also required for RARG-specific antagonist to increase or maintain expression of lamin-A and for agonist to repress expression. The findings extend to a Progerin allele of lamin-A in iPSC-derived MSCs. Consistent with functional synergy, RARG-antagonist treatment drives lamin-A dependent osteogenesis on rigid substrates, with pre-treated xenografts calcifying to a similar extent as native bone. Proteomics-detected targets of mechanosensitive lamin-A and retinoids underscore the convergent synergy of insoluble and soluble cues in differentiation.