Regular articleAdministrations of human adult ischemia-tolerant mesenchymal stem cells and factors reduce amyloid beta pathology in a mouse model of Alzheimer's disease
Introduction
Alzheimer's disease (AD) is a neurodegenerative disorder and the most common form of dementia in the Western world. AD is neuropathologically characterized by the formation of extracellular senile plaques, primarily composed of polymerized amyloid beta (Aβ) peptides and the intracellular deposition of hyperphosphorylated tau proteins into neurofibrillary tangles (Selkoe, 1991). According to the amyloid cascade hypothesis, the extracellular deposition of Aβ is a critical and central event in the disease process leading to the formation of neurofibrillary tangles, neuroinflammation, cell death, and dementia (Hardy and Allsop, 1991). There is no cure on the horizon for this devastating disease that represents one of today's major healthcare challenges due to its severe socio-economic burden (Brookmeyer et al., 2007, Waite, 2015).
Human adult ischemia-tolerant mesenchymal stem cells (hMSCs) constitute a promising therapeutic approach for the treatment of various neurodegenerative disorders including AD (Fan et al., 2014). However, food and drug administration-approved clinical trials currently evaluating the impact of hMSC on AD are marginal. Therefore, an hMSC-based AD therapy represents a large untapped potential waiting to be exploited. Several preclinical research laboratories have reported a beneficial effect of mesenchymal stem cells on cerebral amyloidosis, adult neurogenesis, or memory impairments in models of AD (e.g., Salem et al., 2014, Yan et al., 2014, Yun et al., 2013). However, the majority of these therapeutic initiatives rely on the direct stem cell delivery into the brain through intracerebral or intracerebroventicular injection. These routes of administration entail a major hurdle for clinical applications due to their invasiveness and possible complications (Reyes et al., 2015). This difficulty has certainly hampered to a large extent the clinical translation of these preclinical findings. In contrast, intravenous delivery is fast, easy and complications are rarely observed. To date, only a limited number of preclinical studies have evaluated the impact of intravenous hMSC injections on cerebral amyloidosis (e.g., Kim et al., 2013).
In this present study, we investigated the impact of hMSC and mesenchymal stem cell factors (SCF) on cerebral Aβ pathology in a mouse model of AD. The hMSCs used in this study are bone marrow derived, ischemia-tolerant, cultured under a controlled, low physiological level of oxygen (5%), and manufactured under clinical good manufacturing process conditions. Importantly, these hMSC express negligible levels of human leukocyte antigen-D related (HLA-DR) cell surface receptor and have higher migratory ability as compared to cells cultured at the normal oxygen level (Vertelov et al., 2013). Quantitative reverse transcriptase polymerase chain reaction (RT-PCR) biodistribution revealed that intravenously delivered hMSC are detected in the brain at 1 hour after delivery, decreasing after 1 day, and subsequently dropping below detection level at 1 week after injection. Brain immunohistochemistry demonstrated that intravenously injected hMSCs could be detected in both the cerebrovasculature and in the brain parenchyma. A single intravenous hMSC injection was effective in reducing soluble cerebral Aβ levels at 1 week after delivery in both early and late stage of plaque development. The levels of several major Aβ-degrading enzymes were significantly increased in hMSC-treated mice. In addition, the levels of several proinflammatory cytokines such as Tumor Necrosis Factor alpha (TNFα) were decreased at 1 week after hMSC injection. As a complement to single hMSC delivery, the impact of a repeated intravenous hMSC delivery was investigated on cerebral amyloidosis in APPPS1 mice. Repeated delivery of hMSC (1 injection/wk for 10 weeks) safely reduced cerebral Aβ plaques in both young and aged APPPS1 animals analyzed 1 week after the last injection. Concomitantly, microglial coverage was diminished in hMSC-treated APPPS1 mice. No increase of vascular amyloid or manifestation of microhemorrhages was observed following the repeated intravenous hMSC delivery. Last but not least, in the absence of hMSC injection, proteins secreted by hMSC in culture could also significantly reduce cerebral amyloidosis in APPPS1 mice following repeated intranasal applications for a total of 3 weeks.
In summary, our preclinical results demonstrate that single and repeated intravenous administration of hMSC safely reduces Aβ pathology in the APPPS1 model of AD. The successful reduction of cerebral amyloidosis following intranasal application of hMSC factors invites the next step, that is, clinical studies using these factors as complementary treatment to stem cell injections.
Section snippets
Animals and experimental study design for in vivo experiments
For the in vivo experiments, APPPS1 transgenic mice were obtained from M. Jucker (HIH, Tübingen, Germany) and maintained at the EPFL animal core facility. The mice coexpress under the control of the Thy-1 promoter the KM670/671NL Swedish mutation of human amyloid precursor protein (APP) and the L166P mutation of human presenilin 1 (PS1) and usually show the first amyloid plaques in the cortex at an age of 6–8 weeks. No gender effects in Abeta levels and amyloid deposition are observed in this
Reduction of cerebral soluble Aβ levels in APPPS1 mice following a single injection of hMSC
The Alzheimer model used in this study is the APPPS1 mouse which co-expresses KM670/671NL mutated APP and L166P mutated PS1 under the control of a neuron-specific Thy1 promoter. Cerebral amyloidosis starts in these mice as early as 6–8 weeks of age, and the number of Aβ plaques increases steadily. Single intravenous injections of hMSC were performed in APPPS1 mice (Table 1), and the levels of Aβ42 were analyzed by enzyme-linked immunosorbent assay 1 week after delivery. APPPS1 animals at both
Discussion
In the present work, we have first investigated the impact of a single intravenous hMSC injection in a mouse model of AD and demonstrated that hMSC delivery reduced soluble cerebral Aβ in both young and aged APPPS1 mice at 1 week after delivery. In addition, the levels of several Aβ degrading enzymes were significantly decreased. These results suggest a beneficial impact of hMSC through upregulation of the levels of certain Aβ-degrading enzymes leading to increased Aβ clearance. Analysis of
Conclusions
Adult ischemia-tolerant mesenchymal stem cells (hMSCs) represent a promising yet largely unexploited therapeutic approach for AD. Using a mouse model of cerebral Aβ amyloidosis, we have demonstrated that single and repeated intravenous hMSC injections reduce cerebral Aβ pathology and neuroinflammation with no increase in cerebral amyloid angiopathy or microhemorrhages. Observations of changes in Aβ degrading enzymes and cytokine expression suggest possible mechanisms underlying the actions of
Disclosure statement
The authors declare having competing financial interests. Dr Bolmont, Dr Lukashev, and Cheatham acknowledge their employment at Stemedica International as Chief Scientist, General Manager, and Business Manager, respectively.
Acknowledgements
This work was supported by a grant from the Swiss Commission for Technology and Innovation (BT, PFLS-LS 13964.1). The authors thank Prof Jucker M. (HIH, Tübingen) for providing the APPPS1 animals as well as for insightful comments on the manuscript. The authors thank Dr Yuri Kudinov (StemCutis) for his technical assistance. LA, LT, and BT designed research; HT and ZV performed biodistribution studies; DN and MC performed immunohistological experiments; LY performed quantification analyses; and
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