ABSTRACT
BACKGROUND:Umbilical cord mesenchymal stem cells can be induced to differentiate into hepatocyte-like cells in vitro and in vivo.However,the exact mechanism is still unknown. Existing studies have shown that the Wnt/β-catenin signaling pathway is closely related to this process. OBJECTIVE: To explore the effect of Wnt/β-catenin signaling pathway on the differentiation of umbilical cord mesenchymal stem cells into hepatocyte-like cells and its potential molecular mechanism. METHODS: Human umbilical cord mesenchymal stem cells were extracted from the neonatal umbilical cord by tissue adherent method. After being cultured and purified, the umbilical cord mesenchymal stem cells at passages 4-6 were divided into four groups: control group (DMEM culture group), hepatocyte-like differentiation group, activator Wnt3a group (adding 20 μg/L Wnt3a, an activator of Wnt/β-catenin signaling pathway, under the differentiation condition), and inhibitor Dkk-1 group (adding 20 μg/L Dkk-1, an inhibitor of Wnt/β-catenin signaling pathway, under the differentiation condition). Induced cells were collected respectively on days 7, 14, 21, 28. Their mRNA and protein expressions of α-fetoprotein (AFP), albumin (ALB), hepatocyte nuclear factor 4α (HNF4α) and Cytokeratin-19 (CK-19) in the cells were detected by real-time quantitative PCR and western blot respectively. Meanwhile, Periodic Acid-Schiff staining, low-density lipoprotein uptake test and indocyanine green absorption test were applied to detect the function of hepatocyte-like cells. RESULTS AND CONCLUSION: Compared with the control group, expressions of AFP and HNF4α mRNA and protein as well as ALB mRNA were significantly up-regulated in the hepatocyte-like differentiation group, activator Wnt3a group and inhibitor Dkk-1 group (P < 0.05). Whereas, there was a decrease in the CK-19 expression at mRNA and protein levels (P < 0.01) in these three groups. Compared with the hepatocyte-like differentiation group, the mRNA and protein expressions of AFP and HNF4α, and the mRNA expression of ALB were significantly down-regulated in the activator Wnt3a group (P < 0.05). Compared with hepatocyte-like differentiation group and activator Wnt3a group, the inhibitor Dkk-1 group had higher expression of AFP, HNF4α mRNA and their proteins as well as the mRNA expression of ALB (P <0.05). Findings from the Periodic Acid-Schiff staining, low-density lipoprotein uptake test and indocyanine green absorption test showed more positive cells in the inhibitor Dkk-1 group than in the hepatocyte-like differentiation group and least positive cells in the activator Wnt3a group. Overall, these findings suggest that the inhibition of Wnt/β-catenin signaling pathway promotes the differentiation of umbilical cord mesenchymal stem cells into hepatocyte-like cells;conversely,the cell differentiation can be inhibited via the Wnt/β-catenin pathway.
ABSTRACT
Depression is a major class of mental illness; owing to its high prevalence, high disability rate and heavy disease burden, it has become a stern and formidable global health problem. It is generally believed that the etiology of depression is multifactorial, which is related to gender differences, chronic stress, dietary behavior and drug abuse. At present, the exact pathophysiological mechanism of depression still remains unclear, but researchers across the globe put forward various hypotheses to interpret the possible access to this disease, including monoamine neurotransmitter disturbance, hypothalamic-pituitary-adrenal (HPA) axis dysfunction, lack of neurotrophic factors and excessive pro-inflammatory cytokines. Based on the latest research evidence and the objective fact that traditional antidepressants may be ineffective in some particular patients, the "cytokine theory" tends to attract more and more attention recently. To date, researches on the role of cytokines in the pathogenesis of depression mainly focus on pro-inflammatory cytokines, especially categories including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6). With the proceeding of researches from all over the world, a variety of novel molecules and mechanisms were postulated. This paper summarized a large amount of in vitro and in vivo research evidence, in order to review the current progress of the researches on pathophysiology of depression from the perspective of pro-inflammatory cytokines. Since the response rate of antidepressant therapy during present medical practice is unsatisfying, we suggest a new feasible diagnosis and treatment strategy, that is to distinguish the inflammatory status of patients with depression and take anti-inflammatory treatment into consideration. Totally, this novel strategy aims at modulating the conventional clinical protocol for treatment-resistant depressive patients and overcoming the limitation of insufficient antidepressant response possibly resulted from inflammation.