Alzheimer's disease (AD) is characterized by the deposition of amyloid-b peptide (Ab) and the formation of neurofibrillary tangles. Transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) has been suggested as a potential therapeutic approach to prevent various neurodegenerative disorders, including AD. However, the actual therapeutic impact of BM-MSCs and their mechanism of action in AD have not yet been ascertained. The aim of this study was therefore to evaluate the therapeutic effect of BM-MSC transplantation on the neuropathology and memory deficits in amyloid precursor protein (APP) and presenilin one (PS1) double-transgenic mice. Here we show that intracerebral transplantation of BM-MSCs into APP/PS1 mice significantly reduced amyloid b-peptide (Ab) deposition. Interestingly, these effects were associated with restoration of defective microglial function, as evidenced by increased Ab-degrading factors, decreased inflammatory responses, and elevation of alternatively activated microglial markers. Furthermore, APP/PS1 mice treated with BM-MSCs had decreased tau hyperphosphorylation and improved cognitive function. In conclusion, BM-MSCs can modulate immune/inflammatory responses in AD mice, ameliorate their pathophysiology, and improve the cognitive decline associated with Ab deposits. These results demonstrate that BM-MSCs are a potential new therapeutic agent for AD. STEM CELLS 2010;28:329-343 Disclosure of potential conflicts of interest is found at the end of this article.

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Acid sphingomyelinase activity is increased in brain and plasma of mice and patients with Alzheimer’s disease and its inhibition represents a potential new therapeutic intervention for this disease.

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Recent studies have shown that bone marrow-derived MSCs (BM-MSCs) improve neurological deficits when transplanted into animal models of neurological disorders. However, the precise mechanism by which this occurs remains unknown. Herein we demonstrate that BM-MSCs are able to promote neuronal networks with functional synaptic transmission after transplantation into Niemann-Pick disease type C (NP-C) mouse cerebellum. To address the mechanism by which this occurs, we used gene microarray, whole-cell patch-clamp recordings, and immunohistochemistry to evaluate expression of neurotransmitter receptors on Purkinje neurons in the NP-C cerebellum. Gene microarray analysis revealed upregulation of genes involved in both excitatory and inhibitory neurotransmission encoding subunits of the ionotropic glutamate receptors (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, AMPA) GluR4 and GABA(A) receptor beta2. We also demonstrated that BM-MSCs, when originated by fusion-like events with existing Purkinje neurons, develop into electrically active Purkinje neurons with functional synaptic formation. This study provides the first in vivo evidence that upregulation of neurotransmitter receptors may contribute to synapse formation via cell fusion-like processes after BM-MSC transplantation into mice with neurodegenerative disease. Disclosure of potential conflicts of interest is found at the end of this article.

Microglia have the ability to eliminate amyloid b (Ab) by a cell-specific phagocytic mechanism, and bone marrow (BM) stem cells have shown a beneficial effect through endogenous microglia activation in the brains of Alzheimer's disease (AD) mice. However, the mechanisms underlying BM-induced activation of microglia have not been resolved. Here we show that BM-derived mesenchymal stem cells (MSCs) induced the migration of microglia when exposed to Ab in vitro. Cytokine array analysis of the BM-MSC media obtained after stimulation by Ab further revealed elevated release of the chemoattractive factor, CCL5. We also observed that CCL5 was increased when BM-MSCs were transplanted into the brains of Abdeposited AD mice, but not normal mice. Interestingly, alternative activation of microglia in AD mice was associated with elevated CCL5 expression following intracerebral BM-MSC transplantation. Furthermore, by generating an AD-green fluorescent protein chimeric mouse, we ascertained that endogenous BM cells, recruited into the brain by CCL5, induced microglial activation. Additionally, we observed that neprilysin and interleukin-4 derived from the alternative microglia were associated with a reduction in Ab deposition and memory impairment in AD mice. These results suggest that the beneficial effects observed in AD mice after intracerebral SC transplantation may be explained by alternative microglia activation. The recruitment of the alternative microglia into the brain is driven by CCL5 secretion from the transplanted BM-MSCs, which itself is induced by Ab deposition in the AD brain. STEM CELLS 2012;30:1544-1555 Disclosure of potential conflicts of interest is found at the end of this article.

Although many reports have revealed the importance of defective microglia-mediated amyloid β phagocytosis in Alzheimer’s disease (AD), the underlying mechanism remains to be explored. Here we demonstrate that neurons in the brains of patients with AD and AD mice show reduction of sphingosine kinase1 (SphK1), leading to defective microglial phagocytosis and dysfunction of inflammation resolution due to decreased secretion of specialized proresolving mediators (SPMs). Elevation of SphK1 increased SPMs secretion, especially 15-R-Lipoxin A4, by promoting acetylation of serine residue 565 (S565) of cyclooxygenase2 (COX2) using acetyl-CoA, resulting in improvement of AD-like pathology in APP/PS1 mice. In contrast, conditional SphK1 deficiency in neurons reduced SPMs secretion and abnormal phagocytosis similar to AD. Together, these results uncover a novel mechanism of SphK1 pathogenesis in AD, in which impaired SPMs secretion leads to defective microglial phagocytosis, and suggests that SphK1 in neurons has acetyl-CoA-dependent cytoplasmic acetyltransferase activity towards COX2.

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