Multiple valuable findings
Human neurons (nerve cells from the spinal cord) with an SPG4 mutation have been established and studied, leading to a variety of valuable findings including:
increased axonal swellings indicating the accumulation of axonal transport cargoes (think of slow or jammed traffic)
mitochondrial transport was decreased
spastin protein levels were decreased
acetylated tubulin was increased.
Human neuronal models of hereditary spastic paraplegias (HSP) that recapitulate disease-specific axonal pathology hold the key to understanding why certain axons degenerate in patients and to developing therapies. SPG4, the most common form of HSP, is caused by autosomal dominant mutations in the SPAST gene, which encodes the microtubule-severing ATPase spastin.
Here, we have generated a human neuronal model of SPG4 by establishing induced pluripotent stem cells (iPSCs) from an SPG4 patient and differentiating these cells into telencephalic glutamatergic neurons. The SPG4 neurons displayed a significant increase in axonal swellings, which stained strongly for mitochondria and tau, indicating the accumulation of axonal transport cargoes. In addition, mitochondrial transport was decreased in SPG4 neurons, revealing that these patient iPSC-derived neurons recapitulate disease-specific axonal phenotypes.
Interestingly, spastin protein levels were significantly decreased in SPG4 neurons, supporting a haploin sufficiency mechanism. Furthermore, cortical neurons derived from spastin-knockdown human embryonic stem cells (hESCs) exhibited similar axonal swellings, confirming that the axonal defects can be caused by loss of spastin function. These spastin-knockdown hESCs serve as an additional model for studying HSP.
Finally, levels of stabilized acetylated-tubulin were significantly increased in SPG4 neurons. Vinblastine, a microtubule-destabilizing drug, rescued this axonal swelling phenotype in neurons derived from both SPG4 iPSCs and spastin-knockdown hESCs. Thus, this study demonstrates the successful establishment of human pluripotent stem cell-based neuronal models of SPG4, which will be valuable for dissecting the pathogenic cellular mechanisms and screening compounds to rescue the axonal degeneration in HSP.
SOURCE: Stem Cells. 2013 Oct 7. doi: 10.1002/stem.1569. [Epub ahead of print] Copyright © 2013 AlphaMed Press. PMID: 24123785 [PubMed – as supplied by publisher]
Loss of spastin function results in disease-specific axonal defects in human pluripotent stem cell-based models of hereditary spastic paraplegia.
Denton KR, Lei L, Grenier J, Rodionov V, Blackstone C, Li XJ.
Department of Neuroscience, The University of Connecticut Health Center, Farmington, CT, 06032, USA.