Biology subjects

van Wijnen, A. J.

Publications and source records attributed to van Wijnen, A. J..

3 recordsLinked to original sources

bioRxiv2022

Depletion of Sun1/2 Induces Heterochromatin Accrual in Mesenchymal Stem Cells during Adipogenesis

Critical to the mechano-regulation of mesenchymal stem cells (MSC), Linker of the Nucleoskeleton and Cytoskeleton (LINC) complex transduces cytoskeletal forces to the nuclei. The LINC complex contains outer nuclear membrane Nesprin proteins that associate with the cytoskeleton and their inner nuclear membrane couplers, Sun proteins. In addition to coupling Nesprin-associated cytoskeletal elements to inner nuclear membrane, Sun proteins also function in regulating nuclear mechanics and chromatin tethering to inner nuclear membrane. This suggests that release of LINC-mediated cytoskeletal connections from cell nuclei may have different effects on chromatin organization and MSC differentiation than those due to ablation of intra-nuclear Sun proteins. To test this hypothesis we compared Sun1/2 depletion with expression of the dominant-negative KASH domain (dnKASH) that inhibits Nesprin-Sun association. In cells cultured under adipogenic conditions, disconnecting LINC from the cytoskeleton through dnKASH expression, increased adipogenic gene expression and fat droplet formation; heterochromatin H3K27 and H3K9 methylation was unaltered. In contrast, Sun1/2 depletion inhibited adipogenic gene expression and fat droplet formation; as well the anti-adipogenic effect of Sun1/2 depletion was accompanied by increased H3K9me3, which was enriched on Adipoq, silencing this fat locus. We conclude that releasing the nucleus from cytoskeletal constraints via dnKASH accelerates adipogenesis while depletion of Sun1/2 increases heterochromatin accrual on adipogenic genes in a fashion independent of LINC complex function. Therefore, while these two approaches both disable LINC functions, their divergent effects on the epigenetic landscape indicate they cannot be used interchangeably to study mechanical regulation of cell differentiation.

bioengineering↗

bioRxiv2020

Lamin A/C functions independently from mechanical signaling during adipogenesis

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 protein for nuclear architecture that supports chromatin organization, as well as mechanical integrity and mechano-sensitivity of the nucleus in MSCs. Here, we investigated whether Lamin A/C and mechano-responsiveness are functionally coupled during adipogenesis. Lamin depletion in MSCs using siRNA increased nuclear area, height and volume and decreased circularity and stiffness, while phosphorylation of focal adhesions and dynamic substrate strain in response to LIV remained intact. Lamin A/C depletion decelerates adipogenesis as reflected by delayed appearance of key biomarkers (e.g., adiponectin/ADIPOQ). Based on RNA-seq data, reduced Lamin A/C levels decrease the activation of the adipocyte transcriptome that is normally observed in response to adipogenic cues mediating differentiation of MSCs. Mechanical stimulation via daily LIV application reduced the expression levels of ADIPOQ in both control and Lamin A/C depleted cells. Yet, treatment with LIV did not induce major transcriptome changes in either control or Lamin A/C depleted MSCs, suggesting that the biological effects of LIV on adipogenesis may not occur at the transcriptional level. We conclude that while Lamin A/C activation is essential for normal adipogenesis, it is dispensible for activation of focal adhesions by dynamic vibration induced mechanical signals.

bioengineering↗

bioRxiv2020

Modifiers and Mediators of Craniosynostosis Severity Revealed by Differential Gene Expression

Severity of craniosynostosis in humans varies widely even in patients with identical genetic mutations. In this study we compared RNA sequencing data from cranial tissues of a severe form of Crouzon craniosynostosis syndrome (C57BL/6 FGFR2C342Y/+ mice) with those of a less severe form of Crouzon craniosynostosis (BALB/c FGFR2C342Y/+ mice) to identify genetic modifiers that influence craniosynostosis phenotype severity. Comparison of the mice revealed neonatal onset of coronal suture fusion in the form of suture obliteration in C57BL/6 mice (88% incidence, p<.001 between genotypes). Coronal suture fusion in the form of point fusions across the suture occurred at approximately 4 weeks after birth, with less severe skull shape abnormalities, in BALB/c mice. Substantially fewer genes were differentially expressed in BALB/c FGFR2+/+ vs. FGFR2C342Y/+ mice (87 out of 15,893 expressed genes) than C57BL/6 FGFR2C+/+ vs. FGFR2C342Y/+ mice (2,043 out of 19,097 expressed genes). Further investigation revealed differential expression of coronal suture fusion associated genes, eph/ephrin boundary genes, cell proliferation genes, osteoblast differentiation genes and epigenetic regulators, among others. The most striking pattern in the data was the minimal change in gene expression seen for most genes in BALB/c FGFR2+/+ vs. FGFR2C342Y/+ mice. Analysis of protein processing and lysosomal components support the hypothesis that the craniosynostosis phenotype is less severe in BALB/c mice because the mutant FGFR2C342Y protein is not expressed to the same extent as that seen in C57BL/6 mice. Together, these results suggest that a strategy aimed at increasing degradation of the mutant receptor or downstream signaling inhibition could lead to diminished phenotype severity.

developmental biology↗