Multiple POU-binding motifs, recognized by tissue-specific nuclear factors, are important for Dll1 gene expression in neural stem cells

Biocompatibility evaluation of a 3D-bioprinted alginate-GelMA-bacteria nanocellulose (BNC) scaffold laden with oriented-growth RSC96 cells

Peripheral nerve injury can cause various degrees of damage to the morphological structure and physiological function of the peripheral nerve. At present, compared with "gold standard" autologous nerve transplantation, tissue engineering has certain potential for regeneration and growth; however, achieving oriented guidance is still a challenge. In this study, we used 3D bioprinting to construct a nerve scaffold of RSC96 cells wrapped in sodium alginate/gelatin methacrylate (GelMA)/bacterial nanocellulose (BNC) hydrogel. The 5% sodium alginate+5% GelMA+0.3% BNC group had the thinnest lines among all groups after printing, indicating that the inherent shape of the scaffold could be maintained after adding BNC. Physical and chemical property testing (Fourier transform infrared, rheometer, conductivity, and compression modulus) showed that the 5% alginate+5% GelMA+0.3% BNC group had better mechanical and rheological properties. Live/dead cell staining showed that no mass cell death was observed on days 1, 3, 5, and 7 after printing. In the 5% alginate+5% GelMA group, the cells grew and formed linear connections in the scaffold. This phenomenon was more obvious in the 5% alginate+5% GelMA+0.3% BNC group. In the 5% alginate+5% GelMA+0.3% BNC group, S-100β immunofluorescence staining and cytoskeleton staining showed oriented growth. Polymerase chain reaction (PCR) array results showed that mRNA levels of related neurofactors ASCL1, POU3F3, NEUROG1, DLL1, NOTCH1 and ERBB2 in the 5%GelMA+0.3%BNC group were higher than those of other groups. Four weeks after implantation in nude mice, RSC96 cells grew and proliferated well, blood vessels grew, and S-100β immunofluorescence was positive. These results indicate that a 3D-bioprinted sodium alginate/GelMA/BNC composite scaffold can improve cell-oriented growth, adhesion and the expression of related factors. This 3D-bioprinted composite scaffold has good biocompatibility and is expected to become a new type of scaffold material in the field of neural tissue engineering.

γ-Secretase-regulated mechanisms similar to notch signaling may play a role in signaling events, including APP signaling, which leads to Alzheimer's disease

Although γ-secretase was first identified as a protease that cleaves amyloid precursor protein (APP) within the transmembrane domain, thus producing Aβ peptides that are thought to be pathogenic in Alzheimer's disease (AD), its physiological functions have not been fully elucidated. In the canonical Notch signaling pathway, intramembrane cleavage by γ-secretase serves to release an intracellular domain of Notch that shows activity in the nucleus through binding to transcription factors. Many type 1 transmembrane proteins, including Notch, Delta, and APP, have recently been shown to be substrates for γ-secretase, and their intracellular domains are released from the cell membrane following cleavage by γ-secretase. The common enzyme γ-secretase modulates proteolysis and the turnover of possible signaling molecules, which has led to the attractive hypothesis that mechanisms similar to Notch signaling contribute widely to proteolysis-regulated signaling pathways. APP is also likely to have a signaling mechanism, although the physiological functions of APP have not been elucidated. Indeed, we have shown that the intracellular domain of APP alters gene expression and induces neuron-specific apoptosis. These results suggest that APP signaling responds to the onset of AD. Here, we review the possibility of γ-secretase-regulated signaling, including APP signaling, which leads to AD.

The amyloid precursor protein intracellular domain alters gene expression and induces neuron-specific apoptosis

Although amyloid precursor protein (APP) plays a central role in Alzheimer's disease, the physiological functions of this protein have yet to be fully elucidated. As previously reported, we established an embryonic carcinoma P19 cell line expressing the intracellular domain of APP (AICD). While neurons were differentiated from these cell lines with retinoic acid treatment, expression of AICD induced neuron-specific apoptosis. As the first step to identify the genes involved in this process, we evaluated AICD-induced changes in gene expression through cell death. The levels of expression of 41,256 transcripts were monitored by DNA microarray analysis. The expression of 277 genes showed up-regulation by more than 10-fold in the presence of AICD. Conversely, the expression of 341 genes showed down-regulation to less than one-tenth of the original level. Reverse transcription-polymerase chain reaction of 17 selected genes showed excellent agreement with the microarray results. These results suggest that AICD induces dynamic changes in gene expression, which may be closely correlated with AICD-induced neuron-specific apoptosis.

The intracellular domain of amyloid precursor protein induces neuron-specific apoptosis

Although amyloid precursor protein (APP) has central roles in Alzheimer's disease, the physiological functions of this protein have yet to be fully elucidated. APP homologues show significant sequence conservation in the intracellular domain through evolution, which may reflect the functional importance of the intracellular domain of APP (AICD). To examine this possibility, we established embryonic carcinoma P19 cell lines overexpressing AICD. Although neurons could be differentiated from these cell lines with retinoic acid treatment, overexpression of AICD gave rise to neuron-specific cell death. Furthermore, DNA fragmentation was detected and TUNEL-positive cells were also Tuj1-positive neurons. Taken together, we concluded that AICD can induce neuron-specific apoptosis.

The Delta intracellular domain mediates TGF-beta/Activin signaling through binding to Smads and has an important bi-directional function in the Notch-Delta signaling pathway

Delta is a major transmembrane ligand for Notch receptor that mediates numerous cell fate decisions. The Notch signaling pathway has long been thought to be mono-directional, because ligands for Notch were generally believed to be unable to transmit signals into the cells expressing them. However, we showed here that Notch also supplies signals to neighboring mouse neural stem cells (NSCs). To investigate the Notch-Delta signaling pathway in a bi-directional manner, we analyzed functional roles of the intracellular domain of mouse Delta like protein 1 (Dll1IC). In developing mouse NSCs, Dll1IC, which is released from cell membrane by proteolysis, is present in the nucleus. Furthermore, we screened for transcription factors that bind to Dll1IC and demonstrated that Dll1IC binds specifically to transcription factors involved in TGF-beta/Activin signaling--Smad2, Smad3 and Smad4--and enhances Smad-dependent transcription. In addition, the results of the present study indicated that over-expression of Dll1IC in embryonic carcinoma P19 cells induced neurons, and this induction was blocked by SB431542, which is a specific inhibitor of TGF-beta/Activin signaling. These observations strongly suggested that Dll1IC mediates TGF-beta/Activin signaling through binding to Smads and plays an important role for bi-directional Notch-Delta signaling pathway.