Impaired axonal development and degeneration are implicated in many debilitating disorders, such as hereditary spastic paraplegia (HSP), amyotrophic lateral sclerosis, and periphery neuropathy. HSP is caused by distal axonopathy involving the longest corticospinal tract axons, leading to spasticity and weakness of the lower extremities. The most common early-onset form of HSP, SPG3A, is caused by mutations in the atlastin-1 gene. This gene encodes atlastin-1 protein, which is a member of the dynamin-related large GTPase superfamily. Knockdown of atlastin-1 in rat cortical neuron in vitro cultures inhibits the axonal outgrowth and elongation. However, how altered atlastin-1 activity leads to axonal defects and why specific axons degenerate in HSP patients are largely unclear. The goal of this proposed study is to establish human neuronal models of SPG3A to delineate the mechanisms underlying the axonal defects in HSP. This study's hypothesis is that atlastin mutations result in axonal defects selectively in cortical projection neurons (cortical PNs), and this effect is mediated mainly by dysregulated bone morphogenetic protein (BMP) signaling. This hypothesis will be tested by pursuing the following two aims: 1) to examine the axonal outgrowth and transport in cortical PNs derived from iPSCs that are generated from SPG3A patients and normal individuals (as controls); 2) to delineate the role of BMP signaling in the axonal defects in SPG3A. By comparing the axonal defects, atlastin-1 activity, and BMP signaling alterations in cortical PNs, cortical interneurons, and spinal motor neurons derived from control and SPG3A iPSCs, this study will be able to delineate the cell type-specific defects in HSP and the underlying mechanisms. The cause-effect relationship between loss of atlastin function and axonal phenotypes will be confirmed by knocking down atlastin-1 in wild-type (WT) neurons and by expressing WT atlastin-1 in SPG3A iPSCs. Moreover, rescue experiments will be performed to identify the potential approaches for rescuing the axonal pathology, such as overexpression of atlastin or treatment with BMP antagonists. Together, this study will provide valuable insights into the roles of atlastin-1 and BMP signaling in HSP pathology and developing new therapeutics for rescuing the axonal degeneration in HSP.

Public Health Relevance

HSPs are a group of inherited diseases characterized by distal axonopathy which leads to progressive spasticity and weakness of the legs. This proposed study seeks to delineate the role of BMP signaling in the axonal degeneration in the most common early onset form of HSP, SPG3A, with the ultimate goal of identifying targets and therapeutics for rescuing the axonal degeneration.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Exploratory/Developmental Grants (R21)
Project #
7R21NS089042-03
Application #
9259640
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Gubitz, Amelie
Project Start
2016-04-15
Project End
2017-07-31
Budget Start
2016-04-15
Budget End
2017-07-31
Support Year
3
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Illinois at Chicago
Department
Type
DUNS #
098987217
City
Chicago
State
IL
Country
United States
Zip Code
60612
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Xu, Chong-Chong; Denton, Kyle R; Wang, Zhi-Bo et al. (2016) Abnormal mitochondrial transport and morphology as early pathological changes in human models of spinal muscular atrophy. Dis Model Mech 9:39-49
Denton, Kyle R; Xu, Chongchong; Shah, Harsh et al. (2016) Modeling Axonal Defects in Hereditary Spastic Paraplegia with Human Pluripotent Stem Cells. Front Biol (Beijing) 11:339-354
Boisvert, Erin M; Engle, Sandra J; Hallowell, Shawn E et al. (2015) The Specification and Maturation of Nociceptive Neurons from Human Embryonic Stem Cells. Sci Rep 5:16821