Morphological and neurophysiological impairment of the nerve in type II macrodactyly

Activating PIK3CA mutation promotes adipogenesis of adipose-derived stem cells in macrodactyly via up-regulation of E2F1

Macrodactyly is a congenital malformation characterized by enlargement of bone and soft tissues in limbs, typically with excessive accumulation of adipose tissues. Although gain-of-function mutation of PIK3CA has been identified in macrodactyly, the mechanism of PIK3CA mutation in adipose accumulation is poorly understood. In this study, we found that adipocytes from macrodactyly were more hypertrophic than those observed in polydactyly. PIK3CA (H1047R) activating mutation and enhanced activity of PI3K/AKT pathway were detected in macrodactylous adipose-derived stem cells (Mac-ADSCs). Compared to polydactyly-derived ADSCs (Pol-ADSCs), Mac-ADSCs had higher potential in adipogenic differentiation. Knockdown of PIK3CA or inhibition by BYL-719, a potent inhibitor of PIK3CA, impaired adipogenesis of Mac-ADSCs in vitro. In vivo study, either transient treatment of ADSCs or intragastrical gavage with BYL-719 inhibited the adipose formation in patient-derived xenograft (PDX). Furthermore, RNA-seq revealed that E2F1 was up-regulated in Mac-ADSCs and its knockdown blocked the PIK3CA-promoted adipogenesis. Our findings demonstrated that PIK3CA activating mutation promoted adipogenesis of ADSCs in macrodactyly, and that this effect was exerted by the up-regulation of E2F1. This study revealed a possible mechanism for adipose accumulation in macrodactyly and suggested BYL-719 as a potential therapeutic agent for macrodactyly treatment.

Activating PIK3CA mutation promotes osteogenesis of bone marrow mesenchymal stem cells in macrodactyly

Macrodactyly is a disabling congenital disease characterized by overgrowth of soft tissues and bones, which leads to finger enlargement and joint deformity. The mechanism of bone overgrowth in macrodactyly was rarely understood. In our study bone manifestations of three macrodactyly patients were analyzed by micro-CT. PIK3CA mutation was detected by next-generation sequencing (NGS) of a tumor gene-panel. The PI3K/AKT/mTOR pathway activation and target genes were analyzed. The osteogenic potential of macrodactyly-derived bone marrow mesenchymal stem cells (MAC-BMSCs) was compared with polydactyly-derived bone marrow mesenchymal stem cells (PD-BMSCs). PIK3CA inhibitors were tested for proliferation and osteogenesis potential of MAC-BMSCs. Activating PIK3CA mutations and activation of PI3K/AKT/mTOR pathway were detected in all MAC-BMSCs. MAC-BMSCs had enhanced osteogenesis potential compared with PD-BMSCs. PIK3CA knockdown by shRNA or BYL719 treatment significantly reduced osteogenic differentiation capacity of MAC-BMSCs. RNA-Seq and qRT-PCR revealed the upregulation of distal-less homeobox 5 (DLX5) in MAC-BMSCs compared with PD-BMSCs. The osteogenic potential of MAC-BMSCs was inhibited by DLX5 knockdown, indicating that DLX5 is a downstream target of PIK3CA activation-mediated osteogenesis. This study revealed that osteogenic differentiation in MAC-BMSCs is enhanced by PIK3CA activation mutation through PI3K/AKT/mTOR signaling pathway and can be reversed by PIK3CA knockdown or drug inhibition.