Abstract
The multiplicity of systems affected in Alzheimer’s disease (AD) brains calls for multi-target therapies. Although mesenchymal stem cells (MSC) are promising candidates, their clinical application is limited because of risks related to their direct implantation in the host. This could be overcome by exploiting their paracrine action. We herein demonstrate that in vivo systemic administration of secretome collected from MSC exposed in vitro to AD mouse brain homogenates (MSC-CS), fully replicates the cell-mediated neuroreparative effects in APP/PS1 AD mice. We found a complete but transient memory recovery by 7 days, which vanished by 14 days, after a single MSC-CS intravenous administration in 12-month or 22–24-month-old mice. Treatment significantly reduced plaque load, microglia activation, and expression of cytokines in astrocytes in younger, but not aged, mice at 7 days. To optimize efficacy, we established a sustained treatment protocol in aged mice through intranasal route. Once-weekly intranasal administration of MSC-CS induced persistent memory recovery, with dramatic reduction of plaques surrounded by a lower density of β-amyloid oligomers. Gliosis and the phagocytic marker CD68 were decreased. We found a higher neuronal density in cortex and hippocampus, associated with a reduction in hippocampal shrinkage and a longer lifespan indicating healthier conditions of MSC-CS-treated compared to vehicle-treated APP/PS1 mice. Our data prove that MSC-CS displays a great multi-level therapeutic potential, and lay the foundation for identifying the therapeutic secretome bioreactors leading to the development of an efficacious multi-reparative cocktail drug, towards abrogating the need for MSC implantation and risks related to their direct use.
Highlights
The efficacy of mesenchymal stem cells (MSC)-CS was fully confirmed in a second experiment, showing that MSCCS did not affect memory of wild type (WT) mice (Fig. 1c)
While we demonstrated that conditioning of MSC with Alzheimer’s disease (AD) brain homogenate is necessary to license the therapeutic features of the secretome, we cannot exclude that this effect might be related to inflammatory molecules present in the normal aged brain
We found that APP/PS1 mice treated with MSC-CS appeared to have a much lower Aβ oligomers (AβOs) load around plaques (Fig. 7a, b), which might explain the decrease in the phagocytic commitment of microglia and in the extent of neuroinflammation
Summary
In spite of many advantages of MSC-based therapy, various challenges limit their clinical application, including: (i) invasive cell isolation process, (ii) loss of potency, (iii) limited lifespan, (iv) huge expansion costs [11], as well as the possibility, albeit low, of uncontrollable cell proliferation It is well-accepted that infused MSC act through paracrine mechanisms by releasing bioactive components in their secretome when exposed to an injured environment, rather than through direct engraftment. We establish a preclinical, non-invasive and sustained treatment protocol leading to a reversal of functional and structural damage in aged AD mice These findings hold enormous translational potential, since they provide the opportunity to circumvent the direct implantation of MSC and the limitations related to their clinical application
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