Titolo della tesi: Role of SHh modulation in neurogenesis and tumorigenesis
The SHh pathway plays a major role in a variety of different processes, ranging from embryogenesis to the homeostasis maintenance of adult tissues, with Central Nervous System (CNS) being one of the most SHh signaling-dependent tissues. However, fine-tuning of this pathway is strictly required in order to avoid the in insurgence of pathological conditions. SHh ligand acts indeed as a potent morphogen and mitogen. In the CNS, SHh signaling regulates the various neurogenic processes that occurs during the lifespan of mammals. Sustained SHh signaling in CNS results in the onset of various disease such as medulloblastoma and glioblastoma but, can also lead the de-regulation of the neurogenic process in the adult mammals, impairing the cognitive and behavioral processes underlying these events.
KCASH2KCTD21 (KCASH2 - KCTD Containing Cullin-Adaptor, Suppressor of Hedgehog, 2) is a member of the KCASH protein family, originally discovered in 2011 as a negative regulator of SHh signaling pathway. KCASH2 possesses a BTB/POZ domain that enables the interaction with the E3 ubiquitin ligase Cullin-3. Through this domain, KCASH2 is able to promote interaction between Cullin-3 and the histone deacetylase 1 (HDAC1) and the sub-sequent proteasomal degradation of the latter. Given the role of HDAC1 in de-acetylating the main effector of the SHh pathway, the transcription factor GLI1 (glioma-associated oncogene 1), thus promoting its ability to translocate into the nucleus, the capacity of KCASH2 to reduce the levels of HDAC1 serves therefore as an inhibitory mechanism to turn-off the signaling cascade of SHh pathway.
In this work we examined the in vivo effects of KCASH2 loss on hippocampal neurogenic process. Exploiting a reporter gene we firstly observed KCASH2 expression in the various cell population residing in the hippocampus.
KCASH2 role as a negative regulator of SHh has been confirmed in this context. Indeed, we observed both in vitro and in vivo increased level of GLI1 protein and mRNA. Consistently with these findings we observed a sustained proliferation rate in the hippocampal neurogenic niche in KO mice.
In addition, we analyzed the morphology of the stem cells residing in the hippocampal neurogenic niche. By immunofluorescence analyses we noticed that KCASH2 loss leads to a marked alteration in the morphology of these cells.
The importance of Hh pathway and its cooperative crosstalk with other tumorigenic pathway in the Medulloblastom prompted us to analyze the effects of Hh signaling inhibition on Hh-dependent Medullobalstoma cell lines. We targeted the mechanisms that lead to the activation of GLI1 transcription factor both in a SHh dependent and non-dependent fashion and observed the effects of this inhibition on cell proliferation and survival.
This evidence adds a new layer of complexity in the regulation of hippocampal neurogenesis and the involvement of SHh pathway in this process. Furthermore, our data open new perspectives for the modulation of the Hh pathway in the treatment of Medulloblastoma.