Functional Insights in PLS3-Mediated Osteogenic Regulation

Plastin-3 (PLS3) encodes T-plastin, an actin-bundling protein mediating the formation of actin filaments by which numerous cellular processes are regulated. Loss-of-function genetic defects in PLS3 are reported to cause X-linked osteoporosis and childhood-onset fractures. However, the molecular etiology of PLS3 remains elusive. Functional compensation by actin-bundling proteins ACTN1, ACTN4, and FSCN1 was investigated in zebrafish following morpholino-mediated <i>pls3</i> knockdown. Primary dermal fibroblasts from six patients with a <i>PLS3</i> variant were also used to examine expression of these proteins during osteogenic differentiation. In addition, <i>Pls3</i> knockdown in the murine MLO-Y4 cell line was employed to provide insights in global gene expression. Our results showed that ACTN1 and ACTN4 can rescue the skeletal deformities in zebrafish after <i>pls3</i> knockdown, but this was inadequate for FSCN1. Patients' fibroblasts showed the same osteogenic transdifferentiation ability as healthy donors. RNA-seq results showed differential expression in <i>Wnt1</i>, <i>Nos1ap</i>, and <i>Myh3</i> after <i>Pls3</i> knockdown in MLO-Y4 cells, which were also associated with the <i>Wnt</i> and <i>Th17</i> cell differentiation pathways. Moreover, WNT2 was significantly increased in patient osteoblast-like cells compared to healthy donors. Altogether, our findings in different bone cell types indicate that the mechanism of PLS3-related pathology extends beyond actin-bundling proteins, implicating broader pathways of bone metabolism.