BDNF-, IGF-1- and GDNF-secreting human neural progenitor cells rescue amyloid β-induced toxicity in cultured rat septal neurons

Stem-cell challenges in the treatment of Alzheimer's disease: a long way from bench to bedside

Alzheimer's disease (AD) is the most prevalent type of dementia, and its neuropathology is characterized by deposition of insoluble β-amyloid peptides, intracellular neurofibrillary tangles, and the loss of diverse neurons. Current pharmacological treatments for AD relieve symptoms without affecting the major pathological characteristics of the disease. Therefore, it is essential to develop new and effective therapies. Stem-cell types include tissue-specific stem cells, such as neural stem cells and mesenchymal stem cells, embryonic stem cells derived from blastocysts, and induced pluripotent stem cells (iPSCs) reprogrammed from somatic cells. Recent preclinical evidence suggests that stem cells can be used to treat or model AD. The mechanisms of stem cell based therapies for AD include stem cell mediated neuroprotection and trophic actions, antiamyloidogenesis, beneficial immune modulation, and the replacement of the lost neurons. iPSCs have been recently used to model AD, investigate sporadic and familial AD pathogenesis, and screen for anti-AD drugs. Although considerable progress has been achieved, a series of challenges must be overcome before stem cell based cell therapies are used clinically for AD patients. This review highlights the recent experimental and preclinical progress of stem-cell therapies for AD, and discusses the translational challenges of their clinical application.

Astrocyte-like cells derived from human oral mucosa stem cells provide neuroprotection in vitro and in vivo

Human oral mucosa stem cells (hOMSC) are a recently described neural crest-derived stem cell population. Therapeutic quantities of potent hOMSC can be generated from small biopsies obtained by minimally invasive procedures. Our objective was to evaluate the potential of hOMSC to differentiate into astrocyte-like cells and provide peripheral neuroprotection. We induced hOMSC differentiation into cells showing an astrocyte-like morphology that expressed characteristic astrocyte markers as glial fibrillary acidic protein, S100β, and the excitatory amino acid transporter 1 and secreted neurotrophic factors (NTF) such as brain-derived neurotrophic factor, vascular endothelial growth factor, glial cell line-derived neurotrophic factor, and insulin-like growth factor 1. Conditioned medium of the induced cells rescued motor neurons from hypoxia or oxidative stress in vitro, suggesting a neuroprotective effect mediated by soluble factors. Given the neuronal support (NS) ability of the cells, the differentiated cells were termed hOMSC-NS. Rats subjected to sciatic nerve injury and transplanted with hOMSC-NS showed improved motor function after transplantation. At the graft site we found the transplanted cells, increased levels of NTF, and a significant preservation of functional neuromuscular junctions, as evidenced by colocalization of α-bungarotoxin and synaptophysin. Our findings show for the first time that hOMSC-NS generated from oral mucosa exhibit neuroprotective effects in vitro and in vivo and point to their future therapeutic use in neural disorders.

Axon degeneration is key component of neuronal death in amyloid-β toxicity

Depending upon the stimulus, neuronal cell death can either be triggered from the cell body (soma) or the axon. We investigated the origin of the degeneration signal in amyloid β (Aβ) induced neuronal cell death in cultured in vitro hippocampal neurons. We discovered that Aβ1-42 toxicity-induced axon degeneration precedes cell death in hippocampal neurons. Overexpression of Bcl-xl inhibited both axonal and cell body degeneration in the Aβ-42 treated neurons. Nicotinamide mononucleotide adenylyltransferase 1 (Nmnat1) blocks axon degeneration in a variety of paradigms, but it cannot block neuronal cell body death. Therefore, if the neuronal death signals in Aβ1-42 toxicity originate from degenerating axons, we should be able to block neuronal death by inhibiting axon degeneration. To explore this possibility we over-expressed Nmnat1 in hippocampal neurons. We found that inhibition of axon degeneration in Aβ1-42 treated neurons prevented neuronal cell death. Thus, we conclude that axon degeneration is the key component of Aβ1-42 induced neuronal degeneration, and therapies targeting axonal protection can be important in finding a treatment for Alzheimer's disease.

Co-culture with neurotrophic factor secreting cells induced from adipose-derived stem cells: promotes neurogenic differentiation

Adipose-derived stem cells (ADSCs) and bone marrow stem cells (BMSCs) can be equally proper in the treatment of neurodegenerative diseases. However, ADSCs have practical benefits. In this study, we attempted to induce the secretion of neurotrophic factors (NTF) in human ADSCs. We then evaluated the effects of co-culture with NTF secreting cells in neural differentiation of human ADSCs. Isolated human ADSCs were induced to neurotrophic factors secreting cells. To evaluate the in vitro effects of NTF-secreting ADSCs on neurogenic differentiation of ADSCs, we used neurogenic induction medium (control group), the combination of neurogenic medium and conditioned medium, or co-cultured NTF-secreting ADSCs which were encapsulated in alginate beads (co-culture) for 7 days. ELISA showed increased (by about 5 times) release of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in NTF-secreting ADSCs compared to human ADSCs. Real time RT-PCR analysis revealed that NTF-secreting ADSCs highly expressed NGF and BDNF. In addition, co-culture with NTF-secreting ADSCs could also promote neuronal differentiation relative to gliogenesis. Overall, NTF-secreting ADSCs secrete a range of growth factors whose levels in culture could promote neuronal differentiation and could support the survival and regeneration in a variety of neurodegenerative diseases.

Various roles of astrocytes during recovery from repeated exposure to different doses of lipopolysaccharide

Previous studies have demonstrated that the outcomes associated with neuroinflammation induced by intraperitoneal injection of lipopolysaccharide (LPS) at different dosages vary and either resolve or result in sepsis. The mechanisms underlying differential recoveries from varying doses of LPS are unclear. Additionally, changes in recovery involving chronic or continuous systemic inflammatory responses remain unclear. The present experiments were designed to evaluate the effects of systemic inflammation induced by repeated intraperitoneal injection of LPS at different doses on cognitive impairment. These experiments were also designed to investigate the roles of microglia and astrocytes in systemic inflammation and confirm the mechanisms that influence these processes. Kunming mice were given intraperitoneal injections of LPS at either 5mg/kg or 10mg/kg or saline for 7 consecutive days. Following the 7-day course of injections, a number of mice were kept undisturbed in their home cage for 30 days (30-day recovery), and other mice were similarly kept for 90 days (90-day recovery). The results revealed that the cognitive and physiological changes induced by 5mg/kg LPS included weight loss, impairments in spatial learning and memory, phenotypic changes in glia cells, and altered levels of pro-inflammatory cytokines; all of which were reversible. A potential recovery mechanism involves a neuroprotective function of activated astrocytes that secreted glial-derived neurotrophic factor (GDNF) following 30-day recovery. The changes induced by 10mg/kg LPS included weight loss, phenotypic changes in glia cells, and altered levels of pro-inflammatory cytokines were also reversible; however, a longer recovery was required (90 days). Although 10mg/kg LPS-induced neuroinflammation was reversible, the associated impairments in spatial learning and memory were permanent. A potential mechanism underlying permanent damage associated with 10mg/kg LPS involves the role of the activated astrocytes changing from neuroprotection to destruction, which is mediated by increased pro-inflammatory cytokines in more serious neuroinflammation.

Growth factor receptor-bound protein 10-mediated negative regulation of the insulin-like growth factor-1 receptor-activated signalling pathway results in cognitive disorder in diabetic rats

Growth factor receptor-bound protein 10 (Grb10) is a Src homology 2 domain-containing protein and one of the binding partners for several transmembrane tyrosine kinase receptors, including insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF1-R). The hippocampus, which is critical for cognitive functions, is one of the main distribution areas of Grb10 in the central nervous system. In recent years, diabetic encephalopathy has been defined as a third type of diabetes and the IGF1-IR pathway was shown to be critical for the neuropathogenic process of cognitive disorder in diabetes. However, the role of endogenous Grb10 in regulating the IGF1-IR pathway and neurobehavioural changes is not explicit. The present study aimed to determine the in vivo function of endogenous Grb10 in diabetic encephalopathy and the underlying mechanisms. Using stereotaxic surgical techniques and lentiviral vectors expressing specific short hairpin RNA, we could steadily knockdown Grb10 expression in the hippocampus. More importantly, we demonstrated that hippocampus-specific modulation of Grb10 protein levels led to a prominent remission of cognitive disorder, including improvements in both ultrastructural pathology and abnormal neurobehavioural changes. Our findings indicate that endogenous overexpression of Grb10 functions as a suppressor of the IGF1-IR pathway, which may represent an important mechanism for regulating cognitive disorder in diabetes.

Neuroprotective effect of insulin-like growth factor-1: effects on tyrosine kinase receptor (Trk) expression in dorsal root ganglion neurons with glutamate-induced excitotoxicity in vitro

Insulin-like growth factor-1 (IGF-1) may play an important role in regulating the expression of distinct tyrosine kinase receptor (Trk) in primary sensory dorsal root ganglion (DRG) neurons. Glutamate (Glu) is the main excitatory neurotransmitter and induces neuronal excitotoxicity for primary sensory neurons. It is not known whether IGF-1 influences expression of TrkA, TrkB, and TrkC in DRG neurons with excitotoxicity induced by Glu. In the present study, primary cultured DRG neurons with Glu-induced excitotoxicity were used to determine the effects of IGF-1 on TrkA, TrkB, and TrkC expression. The results showed that IGF-1 increased the expression of TrkA and TrkB and their mRNAs, but not TrkC and its mRNA, in primary cultured DRG neurons with excitotoxicity induced by Glu. Interestingly, neither the extracellular signal-regulated protein kinase (ERK1/2) inhibitor PD98059 nor the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 blocked the effect of IGF-1, but both inhibitors together were effective. IGF-1 may play an important role in regulating different Trk receptor expression in DRG neurons through ERK1/2 and PI3K/Akt signaling pathways. The contribution of distinct Trk receptors might be one of the mechanisms that IGF-1 rescues dying neurons from Glu excitotoxic injury. These data imply that IGF-1 signaling might be a potential target on modifying distinct Trk receptor-mediated biological effects of primary sensory neurons with excitotoxicity.

Effect of low-dose thalidomide on dopaminergic neuronal differentiation of human neural progenitor cells: a combined study of metabolomics and morphological analysis

Thalidomide is increasingly used in anticancer and anti-inflammation therapies. However, it is known for its teratogenicity and ability to induce peripheral neuropathy, although the mechanisms underlying its neurological effect in humans are unclear. In this study, we investigated the effect of thalidomide on the metabolism and neuronal differentiation of human neural progenitor cells. We found that levels of tyrosine, phenylalanine, methionine and glutathione, which are involved in dopamine and methionine metabolism, were decreased following thalidomide treatment. Morphological analysis revealed that treatment with 100 nM thalidomide, which is much lower than clinical doses, significantly decreased the number of dopaminergic (tyrosine hydroxylase-positive) neurons, compared with control cells. Our results suggest that these adverse neurological effects of thalidomide should be taken into consideration prior to its use for the treatment of neurodegenerative and other diseases.

Stem cell therapy for the spinal cord

Injury and disease of the spinal cord are generally met with a poor prognosis. This poor prognosis is due not only to the characteristics of the diseases but also to our poor ability to deliver therapeutics to the spinal cord. The spinal cord is extremely sensitive to direct manipulation, and delivery of therapeutics has proven a challenge for both scientists and physicians. Recent advances in stem cell technologies have opened up a new avenue for the treatment of spinal cord disease and injury. Stem cells have proven beneficial in rodent models of spinal cord disease and injury. In these animal models, stem cells have been shown to produce their effect by the dual action of cell replacement and the trophic support of the factors secreted by these cells. In this review we look at the main clinical trials involving stem cell transplant into the spinal cord, focusing on motor neuron diseases and spinal cord injury. We will also discuss the major hurdles in optimizing stem cell delivery methods into the spinal cord. We shall examine current techniques such as functional magnetic resonance imaging guidance and cell labeling and will look at the current research striving to improve these techniques. With all caveats and future research taken into account, this is a very exciting time for stem cell transplant into the spinal cord. We are only beginning to realize the huge potential of stem cells in a central nervous system setting to provide cell replacement and trophic support. Many more trials will need to be undertaken before we can fully exploit the attributes of stem cells.

Roles of brain-derived neurotrophic factor/tropomyosin-related kinase B (BDNF/TrkB) signalling in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common causes of dementia in the elderly. It is characterized by extracellular deposition of the neurotoxic peptide, amyloid-beta (Aβ) peptide fibrils, and is accompanied by extensive loss of neurons in the brains of affected individuals. However, the pathogenesis of AD is not fully understood. The aim of this review is to discuss the possible role of brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) signalling in the development of AD, focusing on BDNF/TrkB signalling in the production of Aβ, tau hyperphosphorylation and cognition decline, and exploring new possibilities for AD intervention.