Abstracts Category : Other

A Study on the Role of NF-kB Signaling Pathway Members in Regulating Survival Motor Neuron Protein level and in the Pathogenesis of Spinal Muscular Atrophy

by Saravanan Arumugam

Spinal Muscular Atrophy (SMA) is a neuromuscular disorder caused by mutation or loss in SMN1 gene, encoding the ubiquitously expressed Survival Motor Neuron (SMN) protein. SMA is characterized by muscle atrophy, and spinal cord motoneurons (MNs) degeneration. The molecular events behind the selective vulnerability of these MNs to low level of SMN protein are still unknown. The nuclear factor-B (NF-B) pathway has recently been emerged having a vital role related to MN survival, and in neurodegenerative disorders. The NF-B transcription factors regulate genes related to several cellular processes. In the present work, we have analyzed the ability of NF-B pathway members to regulate Smn and their possible role in SMA pathogenesis. The NF-B pathway activation is associated with IKK/IKK phosphorylation, and RelA/p50 nuclear translocation (canonical) or IKK homodimer phosphorylation, and RelB/p52 nuclear translocation (non-canonical). The inhibition of different protein members of both canonical, and non-canonical pathways using shRNA lentiviral transduction methodology in a primary culture of isolated embryonic spinal cord MNs reveals that the selective reduction of RelA induced the reduction of Smn whereas RelB protein reduction had no effect on Smn. In our culture system, reduction of IKK or IKK proteins showed opposite effects on Smn. RT-PCR studies indicate that the shIKK-transduced MNs showed increased Smn mRNA levels, whereas it was not observed changes in Smn mRNA in the case of shIKK- or shRelA-transduced MNs. The double knock-down of IKK and IKK in MNs showed Smn reduction. The knockdown of IKK and/or IKK showed a decrease in RelA phosphorylation, where the phosphorylation of RelA enable RelA/p50 release from its inhibitor in the cytoplasm and facilitates their nuclear translocation. Also, the CREB, one of the transcription factors for Smn was decreased in shIKK, or in shIKK- plus IKK-transduced MNs, and as well as in shRelA-transduced MNs. But, the shIKK MNs exhibited reduced p-RelA but increased CREB level. The shCREB-transduced MNs decreased Smn level, authenticating the regulatory role of CREB on Smn. We observed a reduction in IKK, IKK and p-RelA levels in shSmn-tranduced MNs, and in MNs from a severe type SMA mouse model. Our results show the ability of NF-B canonical pathway to regulate Smn level and, conversely, this pathway is also altered in Smn-deficient MNs. Together, these observations suggest that the NF-B pathway has a role in SMA pathogenesis, and could be a therapeutic target for SMA.Advisors/Committee Members: [emailprotected] (authoremail), false (authoremailshow), Soler i Tatch, Rosa Ma. (director), false (authorsendemail).