Final Report Summary - STEMFORSTROKE (Secretome analysis of intrathecally applied bone marrow stromal cells in experimental stroke.) In the European Union (EU) alone 1.2 million inhabitants suffer a stroke each year. This makes stroke the second most frequent cause of death and the most frequent cause of disability in the EU. Since the acute causal therapy of stroke is limited to a small proportion of patients, the development of regenerative therapies for patients suffering from the chronic consequences of stroke is at urgent need. The therapeutic use of stem cells (SC) has revolutionized the field of regenerative medicine during the last decade. Among the various SC types, bone marrow stromal cells (BMSCs) have been shown to be safe and neuroprotective after experimental stroke. When given systemically (intravenously, IV), however, over 99% of BMSCs are trapped in lung, spleen and kidneys. This off-target distribution of BMSCs may result in serious ectopic side-effects thereby making their use in humans questionable.During the current project we therefore studied the therapeutic potential and the safety profile of BMSCs after ischemic stroke transplanted into the cerebrospinal fluid compartment (CSFc). Our results showed that:1) BMSCs are distributed through the entire CSF compartment after a single ICV infusion. Importantly, our results suggest that the CSF can carry large molecules deep into the brain parenchyma via the paravascular space. These findings imply that CSF may be regarded as an efficient route for drug delivery directly to the injured or ischemic parenchyma.2) We developed a novel mouse stroke model with increased translational efficiency, because we managed to keep animals with large infarcts alive long-term, above the critical period of 14 days post-stroke. This was achieved by applying the same principles as for human post-stroke care (nutrition, fluid balance, temperature control, close monitoring) and without interfering with the course of the disease and its sequels, e.g. brain damage. As such, our developed mouse stroke model is expected to bring preclinical stroke research closer to clinical practice.3) Using this improved mouse stroke model we evaluated the therapeutic potential of 3 different BMSCs types and showed that only BMSCs containing a monocytic component were able to reduce post-ischemic neurological deficits. 4) ICV infused BMSCs do not cause systemic (peripheral) immunomodulation after ICV transplantation and any mode of action is most probably local, via the CSF. These data suggest that the ICV route of transplantation is safe or at least neutral to the systemic immune compartment.5) Our data show for the first time that BMSCs change the composition of CSF when injected ICV, depending on their cell type and origin. They increase activation of the complement system in the CSF and they produce molecules such as MYDGF, CTGF, mesothelin, osteomodulin, TIMP1 etc. Interestingly, our CSF proteomic data support that BMSCs' in vivo secretome is significantly different from the previously reported in vitro one. This highlights -for the first time- that the in vivo mechanisms of action for BMSCs may be entirely different from what were expected or speculated based on vitro experiments, and paves the way for more studies on the in vivo secretome of these cells.6) We show that BMSCs are gradually rejected by the host after their ICV transplantation. This is supported by the presence of apoptotic BMSCs in the ventricular system, the absence of the cells in the CSF 60 days after transplantation, the presence of macrophages/microglia around and in the BMSCs-aggregates, and the high activation of the complement pathway in the CSF. Under this stress, BMSCs respond with production of extracellular matrix components (e.g. laminin) and secretion of factors (e.g. osteomodulin) as a response to the local host and CSF signals. Eventually, as the modified CSF reaches deep parenchymal brain structures (healthy and ischemic ones) via the paravascular space, this can probably explain the modified host's astrocytic and aquaporin-4 reactions during the acute phase.
