Three-dimensional spheroid culture promotes the stemness maintenance of cranial stem cells by activating PI3K/AKT and suppressing NF-κB pathways.

Multipotent stem cells are one of the most powerful tools available for the bone regeneration. However, owing to various limitations, including a lack of tissue-specific stem cell identification, reconstruction of large cranial bone defects remains challenging. In the current study, we isolated a population of Sca-1+CD105+CD140a+ stem cells from adult mouse calvarium and cultured them as three-dimensional spheroids. Although these cells shared similar surface antigens when grown in either monolayers or spheroids, the cranial stem cells grown in spheroids possessed enhanced multipotency and proliferation capacity. In addition, the cranial stem cells in spheroids were found to express high levels of the self-renewal transcription factors Nanog, Oct-4, and Sox-2. Mechanistically, we found that three-dimensional spheroid culture suppressed NF-κB pathways, but activated the PI3K/AKT pathway in cranial stem cells. More importantly, activation of NF-κB pathways or specific inhibition of the PI3K/AKT pathway partially impaired spheroid formation and suppressed expression of self-renewal transcription factors. In summary, these findings reveal a novel effect of spheroid culture in promoting the maintenance of cranial stem cell stemness and indicate that NF-κB and PI3K/AKT pathways might be involved in the stemness maintenance.

Poly(aspartic acid)-based degradable assemblies for highly efficient gene delivery.

Due to its good properties such as low cytotoxicity, degradability, and biocompatibility, poly(aspartic acid) (PAsp) is a good candidate for the development of new drug delivery systems. In this work, a series of new PAsp-based degradable supramolecular assemblies were prepared for effective gene therapy via the host-guest interactions between the cyclodextrin (CD)-cored PAsp-based polycations and the pendant benzene group-containing PAsp backbones. Such supramolecular assemblies exhibited good degradability, enhanced pDNA condensation ability, and low cytotoxicity. More importantly, the gene transfection efficiencies of supramolecular assemblies were much higher than those of CD-cored PAsp-based counterparts at various N/P ratios. In addition, the effective antitumor ability of assemblies was demonstrated with a suicide gene therapy system. The present study would provide a new means to produce degradable supramolecular drug delivery systems.