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Objective: During hair follicle regeneration, hair follicle stem cells (HFSCs) are regulated by signals from dermal papilla cells (DPCs). Previously we found that Tcf4 could promote the proliferation of DPCs. In this study, we focused on whether and how the biological properties of Tcf4-induced DPCs were regulated by Twist1. Methods: Twist1 was overexpressed or knocked down in DPCs following different adenovirus or lentivirus infection. Phase-contrast microscopy was used to observe the agglutinative growth of DPCs. The CCK-8 assay was used to test the proliferation of DPCs. Western blot and qPCR experiments were used to determine the expression of HGF, IGF-1, VEGF, c-myc, survivin, and CyclinD1 in DPCs. ELISAs were used to test the growth factors secreted by DPCs. Conditional medium culture was used to detect the inductive ability of DPCs. Co-immunoprecipitation and immunofluorescence were used to test the binding of Twist1, Tcf4, and β-catenin in DPCs. Immunofluorescence was also used to test the expression of Twist1, Tcf4, and KRT15 in hair follicles. Results: Twist1 induced DPC agglutinative growth and proliferation. Twist1 upregulated the expression of downstream target genes downstream of Tcf4, c-myc, survivin, in Tcf4-induced DPCs, as well as the expression and secretion of growth factors HGF, IGF-1, VEGF, which had the ability to induce hair follicle growth. The conditional medium from Twist1-treated DPCs increased the expression of KRT40 and MSX2 in HaCaT cells. Twist1 and Tcf4 co-localized in DPCs both in vitro and in vivo. Anti-Twist1 precipitated Tcf4 and β-catenin. Conclusion: These results indicate that Tcf4 and Twist1 play a synergistic role in regulating the hair follicle induction ability of DPCs. Twist1 functions by forming a ternary complex with Tcf4 and β-catenin. Thus, we report new data that elucidate whether and how Twist1 regulates some biological properties of DPCs.

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An electrochemical biosensor was developed for the detection of adenosine triphosphate (ATP) based on target-induced conformation switching and nicking endonuclease (NEase)-assisted signal amplification. The electrochemical biosensor was constructed by base pairing and target recognition. After capture DNA hybridized with the gold electrode, a significant current of Methylene Blue (MB) was obtained by differential pulse voltammetry. In the presence of ATP, the hairpin DNA formed a G-quadruplex structure due to the specific recognition between hairpin DNA and ATP. Then the exposed part of the target-aptamer complex hybridized with the 3'-terminus of capture DNA to form a specific nicking site for Nb.BbvCI, which led to NEase-assisted target-aptamer complex recycling. The released target-aptamer complex hybridized with the remaining capture DNA. Nb.BbvCI-assisted target-aptamer complex recycling caused the continuous cleavage of capture DNA with MB at its 5'-terminus, resulting in release of a certain amount of DNA fragment labeled with MB. Then the current value decreased significantly. The reduced current showed a linear range from 10 nM to 1 μM with a limit of detection as low as 3.4 nM. Furthermore, the proposed strategy can be used for the detection of similar substances.