Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved drug, which minimally extends patient survival. Here, we investigated pathophysiological mechanisms underlying ALS using motor neurons (MNs) differentiated from induced pluripotent stem cells (iPSCs) derived from ALS patients carrying mutations in FUS or SOD1. Patient-derived MNs were less active and excitable compared to healthy controls, due to reduced Na 1 /K 1 ratios in both ALS groups accompanied by elevated potassium channel (FUS) and attenuated sodium channel expression levels (FUS, SOD1). ALS iPSC-derived MNs showed elevated endoplasmic reticulum stress (ER) levels and increased caspase activation. Treatment with the FDA approved drug 4-Aminopyridine (4AP) restored ion-channel imbalances, increased neuronal activity levels and decreased ER stress and caspase activation. This study provides novel pathophysiological data, including a mechanistic explanation for the observed hypoexcitability in patient-derived MNs and a new therapeutic strategy to provide neuroprotection in MNs affected by ALS. STEM CELLS 2016;34:1563-1575 SIGNIFICANCE STATEMENTOur primary objective was to characterize the neurophysiology of iPSC-based models of amyotrophic lateral sclerosis (ALS) and, based on these results, to prevent neurodegeneration using targeted pharmacological intervention. We observed that mutant FUS and SOD1 iPSC-derived motor neurons displayed hypoexcitability, which recently has been shown to be a promising target to increase resilience against ALS-associated neurodegeneration. We identified the molecular mechanisms causing this phenotype, which enabled us to define a new therapeutic strategy using the FDA-approved drug 4-Aminopyridine. 4-Aminopyridine is a potassium channel blocker that raised motor neuronal activity and decreased endoplasmic reticulum stress and caspase activation. Our results provide novel pathophysiological data and an innovative treatment concept for symptomatic and neuroprotective therapy in ALS that stands in contrast to current strategies.

Highlights d SENP3 regulates sarcomere assembly by regulating molecular motor gene MyHC-II d SENP3 expression is temporally regulated in differentiated myotubes d By regulating SETD7, SENP3 affects association of Pol II and Suv39h1 on MyHC-II d SENP3 is degraded in cachexia, resulting in disordered sarcomeric structure

We have previously shown that knockout of fibroblast growth factor-2 (FGF-2) and potential compensatory effects of other growth factors result in amelioration of disease symptoms in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). ALS is a rapidly progressive neurological disorder leading to degeneration of cortical, brain stem, and spinal motor neurons followed by subsequent denervation and muscle wasting.Mutations in the superoxide dismutase 1 (SOD1) gene are responsible for approximately 20% of familial ALS cases and SOD1 mutant mice still are among the models best mimicking clinical and neuropathological characteristics of ALS. The aim of the present study was a thorough characterization of FGF-2 and other growth factors and signaling effectors in vivo in the SOD1 G93A mouse model. We observed tissue-specific opposing gene regulation of FGF-2 and overall dysregulation of other growth factors, which in the gastrocnemius muscle was associated with reduced downstream extracellular-signalregulated kinases (ERK) and protein kinase B (AKT) activation. To further investigate whether the effects of FGF-2 on motor neuron death are mediated by glial cells, astrocytes lacking FGF-2 were cocultured together with mutant SOD1 G93A motor neurons. FGF-2 had an impact on motor neuron maturation indicating that astrocytic FGF-2 affects motor neurons at a developmental stage. Moreover, neuronal gene expression patterns showed FGF-2-and SOD1 G93A -dependent changes in ciliary neurotrophic factor, glial-cell-linederived neurotrophic factor, and ERK2, implying a potential involvement in ALS pathogenesis before the onset of clinical symptoms.

Cellular therapy represents a novel option for the treatment of neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS). Its major aim is the generation of a protective environment for degenerating motor neurons. Mesenchymal stromal cells secrete different growth factors and have antiapoptotic and immunomodulatory properties. They can easily and safely be isolated from human bone marrow and are therefore considered promising therapeutic candidates. In the present study, we compared intraventricular application of human mesenchymal stromal cells (hMSCs) versus single and repeated intraspinal injections in the mutant SOD1 G93A transgenic ALS mouse model. We observed significant reduction of lifespan of animals treated by intraventricular hMSC injection compared with the vehicle treated control group, accompanied by changes in weight, general condition, and behavioural assessments.A potential explanation for these rather surprising deleterious effects lies in increased microgliosis detected in the hMSC treated animals. Repeated intraspinal injection at two time points resulted in a slight but not significant increase in survival and significant improvement of motor performance although no hMSC-induced changes of motor neuron numbers, astrogliosis, and microgliosis were detected. Quantitative real time polymerase chain reaction showed reduced expression of endothelial growth factor in animals having received hMSCs twice compared with the vehicle treated control group. hMSCs were detectable at the injection site at Day 20 after injection into the spinal cord but no longer at Day 70. Intraspinal injection of hMSCs may therefore be a more promising option for the treatment of ALS than intraventricular injection and repeated injections might be necessary to obtain substantial therapeutic benefit. KEYWORDS amyotrophic lateral sclerosis, human mesenchymal stromal cells, immunohistochemistry, intraspinal injection, intrathecal injection, motor function, SOD1 G93A mouse model

Amyotrophic Lateral Sclerosis (ALS) is a degenerative motor neuron disorder. It is supposed that ALS is at least in part an axonopathy. Neuropilin 1 is an important receptor of the axon repellent Semaphorin 3A and a co‐receptor of vascular endothelial growth factor. It is probably involved in neuronal and axonal de‐/regeneration and might be of high relevance for ALS pathogenesis and/or disease progression. To elucidate whether the expression of either Neuropilin1 or Semaphorin3A is altered in ALS we investigated these proteins in human brain, spinal cord and muscle tissue of ALS‐patients and controls as well as transgenic SOD1G93A and control mice. Neuropilin1 and Semaphorin3A gene and protein expression were assessed by quantitative real‐time PCR (qRT‐PCR), western blot and immunohistochemistry. Groups were compared using either Student t‐test or Mann–Whitney U test. We observed a consistent increase of Neuropilin1 expression in the spinal cord and decrease of Neuropilin1 and Semaphorin3A in muscle tissue of transgenic SOD1G93A mice at the mRNA and protein level. Previous studies have shown that damage of neurons physiologically causes Neuropilin1 and Semaphorin3A increase in the central nervous system and decrease in the peripheral nervous system. Our results indicate that this also occurs in ALS. Pharmacological modulation of expression and function of axon repellents could be a promising future therapeutic option in ALS.