Activation of canonical Wnt signaling pathway promotes proliferation and self-renewal of rat hepatic oval cell line WB-F344 in vitro

AIM： To investigate the effect of activation of canonical Wnt signaling pathway on the proliferation and differentiation of hepatic oval cells in vitro. METHODS： WB-F344 cells were treated with recombinant Wnt3a （20, 40, 80, 160, 200 ng/mL） in serum-free medium for 24 h. Cell proliferation was measured by Brdu incorporation analysis; untreated WB-F344 cells were taken as controls. After treatment with Wnt3a （160 ng/mL） for 24 h, subcellular localization and protein expression of p-catenin in WB-F344 cells treated and untreated with Wnt3a were examined by immunofluorescence staining and Western blot analysis. CyclinD1 mRNA expression was determined by semi-quantitative reverse-transcript polymerase chain reaction （RT-PCR）. The mRNA levels of some phenotypic markers （AFP, CK-19, ALB） and two hepatic nuclear factors （HNF-4, HIVF-6） were measured by RT-PCR. Expressions of CK-19 and AFP protein were detected by Western blot analysis. RESULTS： Wnt3a promoted proliferation of WB-F344 cells. Stimulation of WB-F344 cells with recombinant Wnt3a resulte^l in accumulation of the transcriptional activator β-catenin, together with its translocation into the nuclei, and up-regulated typical Wnt target gene CyclinD1. After 3 d of Wnt3a treatment in the absence of serum, WB-F344 cells retained their bipotential to express several specific phenotypic markers of hepatocytes and cholangiocytes, such as AFP and CK-19, following activation of the canonical Wnt signaling pathway. CONCLUSION： The canonical Wnt signaling pathway promotes proliferation and self-renewal of rat hepatic oval cells.

Angiogenesis in a 3D model containing adipose tissue stem cells and endothelial cells is mediated by canonical Wnt signaling

Adipose-derived stromal cells （ASCs） have gained great attention in regenerative medicine. Progress in our understanding of adult neovascularization further suggests the potential of ASCs in promoting vascular regeneration, although the specific cues that stimulate their angiogenic behavior remain controversial In this study, we established a three-dimensional （3D） angiogenesis model by co-culturing ASCs and endothelial cells （ECs） in collagen gel and found that ASC-EC-instructed angiogenesis was regulated by the canonical Wnt pathway. Furthermore, the angiogenesis that occurred in implants collected after injections of our collagen gel- based 3D angiogenesis model into nude mice was confirmed to be functional and also regulated by the canonical Wnt pathway. Wnt regulation of angiogenesis involving changes in vessel length, vessel density, vessel sprout, and connection numbers occurred in our system. Wnt signaling was then shown to regulate ASC- mediated paracrine signaling during angiogenesis through the nuclear translocation of β-catenin after its cytoplasmic accumulation in both ASCs and ECs. This translocation enhanced the expression of nuclear cofactor Lef-1 and cyclin D1 and activated the angiogenic transcription of vascular endothelial growth factor A （VEGFA）, basic fibroblast growth factor （bFGF）, and insulin-like growth factor 1 （IGF-1）. The angiogenesis process in the 3D collagen model appeared to follow canonical Wnt signaling, and this model can help us understand the importance of the canonical Wnt pathway in the use of ASCs in vascular regeneration.

The human and mouse sex-determining SRY genes repress the Rspo1/β-catenin signaling

The sex-determining region Y （SRY） is the gene on the Y chromosome responsible for switching on male sex determination during mammalian embryogenesis. In its absence, ovaries develop in the embryo. Hence, ovarian determination and differentiation is considered to be a default, or passive, developmental pathway. Recently this classical paradigm of sex determination has been challenged with the discovery of the R-spondin 1 （RSPO1） as an active ovarian determinant. Mutations of RSPO1 cause a female-to-male sex reversal. RSPO1 synergizes with WNT4 in activating an ovarian development in the bipotential gonad via the canonical Wnt signaling. Early studies showed that SRY represses such Wnt signaling, but also generated discrepancies on whether only mouse Sry is capable of inhibiting such Wnt signaling and whether both human and mouse SRY proteins are able to interact with β-catenin, the intracellular messenger responsible for executing the Wnt signals. Our studies show that both human SRY and mouse Sry are capable of repressing the Rspol/Wnt/β-catenin signaling. However, the repression activities vary among different SRY/Sry proteins and paradoxically related to the presence and/or size of an acidic/glutamine-rich domain. The HMG box of human SRY could bind directly to β-catenin while the mouse Sry binds to β-catenin via its HMG box and glutamine-rich domain. The results clarify some of the initial discrepancies, and raise the possibility that SRY interacts with β-catenin in the nucleus and represses the transcriptional activation of the Rspol/Wnt target genes involved in ovarian determination, thereby switching on testis determination.