In the current study Olfml knockdown increased
In the current study, Olfml1 knockdown increased YAP but decreased the respective target genes of canonical Wnt signaling and Hedgehog signaling, Axin2 and Gli1. YAP suppresses canonical Wnt via binding to Dishevelled and/or β-catenin [, , , ]. Tariki et al. reported that adenovirus-mediated overexpression of YAP prevented Hedgehog signaling, while RNA interference-mediated knockdown of endogenous YAP augmented Hedgehog signaling in murine embryonic fibroblasts (MEF), HEK293T, pancreatic stellate cells, and NIH3T3 Indoximod . Our data support those findings.
In an earlier study, Wan et al. transfected plasmids encoding the c-Myc-tagged human OLFML1 (hOLFML1) into COS-7 cells and detected hOLFML1 in both cell lysates and culture medium. They also showed that transfection of hOLFML1 promoted the proliferation of HeLa cells . We observed that mOlfml1 was present in the cytoplasm and co-localized with YAP. In addition, knockdown of Olfml1 did not affect osteoblast survival rate. Functional differences are possible between human OLFML1 and murine Olfml1. There is also the possibility of a functional discrepancy of OLFML1 between murine primary osteoblasts and the human cervical cancer HeLa cell line. Further investigation is required on the physiological roles of intracellular and extracellular OLFML1.
In conclusion, our cumulative findings demonstrate a role of Olfml1 in osteoblast mineralization as an endogenous inhibitor of the Hippo signaling pathway. The mechanism by which the nuclear translocation of YAP is arrested requires additional study, and the link between congenital scoliosis and OLFML1 mutations will need clarification. Further examination of the mutant mice or case reports will elucidate these issues.
Acknowledgments We would like to thank all family members of this congenital scoliosis case for their contributions. The authors also thank the members of the bone club at Matsumoto Dental University for stimulating discussion. This work was supported by a grant from Japan Society for the Promotion of Science KAKENHI grants [15K10395 (Y. N.)].
Introduction A primary function of the gut epithelium is nutrient uptake and forming a protective barrier against the external milieu. To maintain barrier function the epithelium is continuously renewed by intestinal stem cells (ISCs), or crypt base columnar cells (CBCs), located in the crypts of Lieberkühn (Figure 1). Over the last decade significant progress has been made in our understanding how ISCs function during homeostasis , but less is known about gut epithelial regeneration upon damage and how chronic injury is linked to cancer initiation and progression. In models of gut injury, such as whole body irradiation or dextran sodium sulfate (DSS)-induced colitis, surviving cells of the crypts undergo a rapid, transient proliferative boost that replenishes non-functional cells. Increased Wnt, Egfr and Jak/Stat signalling are important in this response [2, 3, 4, 5, 6], while the recent discovery of the Hippo pathway has revealed an additional layer of complexity . The core Hippo pathway in mammals includes the Mst and Lats kinase cassette (see Box 1 for details), which inactivates the transcriptional regulators, Yap and Taz that in turn regulate transcription of genes typically associated with proliferation, cell survival and cell fate. Loss of function studies in vivo have shown that Yap and Taz are dispensable for gut homeostasis, but following chemical injury or gamma irradiation, Yap is required to regenerate the Lgr5+ ISC pool and crypt regeneration [8, 9, 10••]. One exception is the work of Imajo et al., who used a novel intestinal RNAi delivery system  and suggested Yap/Taz promote ISC proliferation and differentiation into goblet cells without prior injury. However, the Yap/Taz dependent effects observed in their system might reflect induction of tissue injury responses from the surgical interventions required for virus-mediated gene transfer. Collectively, the studies on Hippo signalling in the gut indicate that under normal circumstances Yap/Taz are tightly controlled by the inhibitory upstream kinases Mst and Lats that is released during regenerative responses.