Concise Review: Increasing the Validity of Cerebrovascular Disease Models and Experimental Methods for Translational Stem Cell Research.

Interspecies differences, anatomical and physiological aspects, as wells as simplified study designs contribute to an overestimation of treatment effects and limit the transferability of experimental results into clinical applications. Confounders of cell therapies for cerebrovascular disorders (CVD) include common CVD comorbidities, frequent medications potentially affecting endogenous and transplanted stem cells, as well as age- and immune-system-related effects. All those can contribute to a substantial modeling bias, ultimately limiting the prospective quality of preclinical research programs regarding the clinical value of a particular cell therapy. In this review, we discuss the nature and impact of most relevant confounders. We provide suggestions on how they can be considered to enhance the validity of CVD models in stem cell research. Acknowledging substantial and sometimes surprising effects of housing conditions, chronobiology, and intersex differences will further augment the translational value of animal models. We finally discuss options for the implementation of high-quality functional and imaging readout protocols. Altogether, this might help to gain a more holistic picture about the therapeutic impact of a particular cell therapy for CVD, but also on potential side and off-site effects of the intervention. Stem Cells 2017;35:1141-1153.

High-dosage granulocyte colony stimulating factor treatment alters monocyte trafficking to the brain after experimental stroke.

Ischemic stroke elicits a prompt inflammatory response that is characterized by a well-timed recruitment of peripheral immune cells to the brain. Among these, monocytes play a particularly important, but multifaceted role and have been increasingly recognized to affect stroke outcome. Granulocyte colony stimulating factor (GCSF) is known for its immunosuppressive actions on mononuclear cells, but previous studies in the stroke field were mainly confined to its neuroprotective actions. Herein, we investigated whether GCSF affects post-stroke inflammation in a mouse model of focal brain ischemia by modulating monocyte responses. Treatment with GCSF was controlled by vehicle injection, sham surgery and naive animals. Despite a significant monocytosis, high-dosage GCSF reduced the number of brain-infiltrating monocytes/macrophages four days after stroke. Lower numbers of mononuclear phagocytes in the brain were associated with smaller cerebral edema and improved motor outcome after stroke. GCSF treatment over 72h, but not 24h diminished integrin expression on circulating Ly6C+ inflammatory monocytes. In vitro experiments further revealed that GCSF strongly promotes interleukin (IL)-10 secretion by activated mononuclear cells. Blockade of the IL-10 receptor partly reversed GCSF-induced downregulation of integrin surface expression. Overall, our results suggest that high-dosage GCSF mitigates monocyte infiltration after stroke, likely by attenuating integrin-mediated adhesion to the brain endothelium in an IL-10-dependent manner. Lower amounts of mononuclear cells in the brain translate to less severe brain edema and functional impairment and thus support a harmful role of Ly6C+ inflammatory monocytes in the acute stage of stroke.

Allometric dose retranslation unveiled substantial immunological side effects of granulocyte colony-stimulating factor after stroke.

BACKGROUND AND PURPOSE: Granulocyte colony-stimulating factor (GCSF) showed robust neuroprotective and neuroregenerative properties after stroke in rodents but failed to meet study end points in patients. Because immunologic side effects of GCSF may have escaped preclinical testing because of nonallometric dose translation, we hypothesized those as possible reasons. METHODS: Stroke was induced in C57BL/6 mice by 45-minute filament middle cerebral artery occlusion. GCSF was administered at 50 and 832.5 µg/kg body weight. Treatment was controlled by vehicle injection, sham surgery, and naive animals. Immune cell counts were assessed in blood, spleen, and brain by multidimensional flow cytometry 1 day after stroke. RESULTS: High-dose GCSF significantly altered myeloid and T-cell subpopulations in blood and spleen and caused a tremendous increase of monocytes/macrophages infiltrating the ischemic brain. CONCLUSIONS: Dose-dependent immunomodulation superimposes central nervous system-specific effects of GCSF after stroke. Adaption of dose or treatment time may overcome this drawback.

Bone marrow cell transplantation time-dependently abolishes efficacy of granulocyte colony-stimulating factor after stroke in hypertensive rats.

BACKGROUND AND PURPOSE: We aimed to determine a possible synergistic effect of granulocyte colony-stimulating factor (G-CSF) and bone marrow-derived mononuclear cells (BM MNC) after stroke in spontaneously hypertensive rats. METHODS: Male spontaneously hypertensive rats were subjected to middle cerebral artery occlusion and randomly assigned to daily injection of 50 µg/kg G-CSF for 5 days starting 1 hour after stroke (groups 1, 2, and 3) with additional intravenous transplantation of 1.5×10E7 BM MNC per kilogram at 6 hours (group 2) or 48 hours (group 3) after stroke, or control treatment (group 4). Circulating leukocyte counts and functional deficits, infarct volume, and brain edema were repeatedly assessed in the first week and first month. RESULTS: G-CSF treatment led to a significant neutrophilia, to a reversal of postischemic depression of circulating leukocytes, and to a significantly improved functional recovery without affecting the infarct volume or brain edema. BM MNC cotransplantation was neutral after 6 hours, but reversed the functional effect of G-CSF after 48 hours. Short-term investigation of combined G-CSF and BM MNC treatment at 48 hours indicated splenic accumulation of granulocytes and transplanted cells, accompanied by a significant rise of granulocytes in the circulation and the ischemic brain. CONCLUSIONS: G-CSF improved functional recovery in spontaneously hypertensive rats, but this effect was abolished by cotransplantation of BM MNC after 48 hours. In the spleen, transplanted cells may hinder the clearance of granulocytes that were massively increased by G-CSF. Increased circulation and infiltration of granulocytes into the ischemic brain may be detrimental for stroke outcome.

Isolation and Flow Cytometric Analysis of Immune Cells from the Ischemic Mouse Brain.

Ischemic stroke initiates a robust inflammatory response that starts in the intravascular compartment and involves rapid activation of brain resident cells. A key mechanism of this inflammatory response is the migration of circulating immune cells to the ischemic brain facilitated by chemokine release and increased endothelial adhesion molecule expression. Brain-invading leukocytes are well-known contributing to early-stage secondary ischemic injury, but their significance for the termination of inflammation and later brain repair has only recently been noticed. Here, a simple protocol for the efficient isolation of immune cells from the ischemic mouse brain is provided. After transcardial perfusion, brain hemispheres are dissected and mechanically dissociated. Enzymatic digestion with Liberase is followed by density gradient (such as Percoll) centrifugation to remove myelin and cell debris. One major advantage of this protocol is the single-layer density gradient procedure which does not require time-consuming preparation of gradients and can be reliably performed. The approach yields highly reproducible cell counts per brain hemisphere and allows for measuring several flow cytometry panels in one biological replicate. Phenotypic characterization and quantification of brain-invading leukocytes after experimental stroke may contribute to a better understanding of their multifaceted roles in ischemic injury and repair.

Granulocyte colony-stimulating factor and bone marrow mononuclear cells for stroke treatment in the aged brain.

Ischemic stroke swiftly induces a wide spectrum of pathophysiological sequelae, particularly in the aged brain. The translational failure of experimental therapies, might partially be related to monotherapeutic approaches, not address potential counter-mechanisms sufficiently or within the best time window. For example, therapeutic effects relying on stem/progenitor cell mobilization by granulocyte-colony stimulating factor (G-CSF), require approximately a week to become manifest, which is potentially beyond the optimal timing. Here, We tested the hypothesis that treating post-stroke aged rats with the combination of bone marrow-derived mononuclear cells (BM MNC) and G-CSF improves the long term (56 days) functional outcome by compensating the delay before G-CSF effects come to full effect. 1x10(6) syngeneic BM MNC per kg bodyweight (BW) with G-CSF (50 µg/kg, given intraperitoneal by via the jugular vein to aged Sprague- Dawley rats, six hours post-stroke. This process was repeated daily, for a 28 day period. Infarct volume was measured by magnetic resonance imaging at 3 and 48 days post-stroke and additionally by immunohistochemistry at day 56. Functional recovery was tested during the entire post-stroke survival period. Daily G-CSF treatment led to a robust and consistent improvement of neurological function, but did not alter final infarct volumes. The combination of G-CSF and BM MNC, did not further improve post-stroke recovery. The lack of an additional benefit may be due to interaction between both approaches, and to a lesser extent, in the insensitivity of the aged brains' regenerative mechanisms. Also considering recent findings on other tandem approaches involving G-CSF in animal models featuring relevant co-morbidities, we conclude that such combination therapies are not the optimal approach to treat the acutely injured aged brain.

Arterial Hypertension Aggravates Innate Immune Responses after Experimental Stroke.

Arterial hypertension is not only the leading risk factor for stroke, but also attributes to impaired recovery and poor outcome. The latter could be explained by hypertensive vascular remodeling that aggravates perfusion deficits and blood-brain barrier disruption. However, besides vascular changes, one could hypothesize that activation of the immune system due to pre-existing hypertension may negatively influence post-stroke inflammation and thus stroke outcome. To test this hypothesis, male adult spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKYs) were subjected to photothrombotic stroke. One and 3 days after stroke, infarct volume and functional deficits were evaluated by magnetic resonance imaging and behavioral tests. Expression levels of adhesion molecules and chemokines along with the post-stroke inflammatory response were analyzed by flow cytometry, quantitative real-time PCR and immunohistochemistry in rat brains 4 days after stroke. Although comparable at day 1, lesion volumes were significantly larger in SHR at day 3. The infarct volume showed a strong correlation with the amount of CD45 highly positive leukocytes present in the ischemic hemispheres. Functional deficits were comparable between SHR and WKY. Brain endothelial expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and P-selectin (CD62P) was neither increased by hypertension nor by stroke. However, in SHR, brain infiltrating myeloid leukocytes showed significantly higher surface expression of ICAM-1 which may augment leukocyte transmigration by leukocyte-leukocyte interactions. The expression of chemokines that primarily attract monocytes and granulocytes was significantly increased by stroke and, furthermore, by hypertension. Accordingly, ischemic hemispheres of SHR contain considerably higher numbers of monocytes, macrophages and granulocytes. Exacerbated brain inflammation in SHR may finally be responsible for larger infarct volumes. These findings provide an immunological explanation for the epidemiological observation that existing hypertension negatively affects stroke outcome and mortality.

Comprehensive characterization of chondrocyte cultures in plasma and whole blood biomatrices for cartilage tissue engineering.

Many synthetic polymers and biomaterials have been used as matrices for 3D chondrocyte seeding and transplantation in the field of cartilage tissue engineering. To develop a fully autologous carrier for chondrocyte cultivation, we examined the feasibility of allogeneic plasma and whole blood-based matrices and compared them to agarose constructs. Primary articular chondrocytes isolated from 12-month-old pigs were embedded into agarose, plasma and whole blood matrices and cultivated under static-free swelling conditions for up to four weeks. To evaluate the quality of the synthesized extracellular matrix (ECM), constructs were subjected to weekly examinations using histological staining, spectrophotometry, immunohistochemistry and biochemical analysis. In addition, gene expression of cartilage-specific markers such as aggrecan, Sox9 and collagen types I, II and X was determined by RT-PCR. Chondrocyte morphology was assessed via scanning electron microscopy and viability staining, including proliferation and apoptosis assays. Finally, (13) C NMR spectroscopy provided further evidence of synthesis of ECM components. It was shown that chondrocyte cultivation in allogeneic plasma and whole-blood matrices promoted sufficient chondrocyte viability and differentiation behaviour, resulting in neo-formation of a hyaline-like cartilage matrix.

Sterile inflammation after permanent distal MCA occlusion in hypertensive rats.

The pathophysiology of stroke is governed by immune reactions within and remote from the injured brain. Hypertension, a major cause and comorbidity of stroke, entails systemic vascular inflammation and may influence poststroke immune responses. This aspect is, however, underestimated in previous studies. Here we aimed to delineate the sequence of cellular inflammation after stroke in spontaneously hypertensive (SH) rats. Spontaneously hypertensive rats were subjected to permanent middle cerebral artery occlusion and killed after 1 or 4 days. Immune cells of the peripheral blood and those which have infiltrated the injured brain were identified and quantified by flow cytometry. The spatial distribution of myeloid cells and T lymphocytes, and the infarct volume were assessed by histology. We observed a concerted infiltration of immune cells into the ischemic brain of SH rats. At day 1, primarily neutrophils, monocytes, macrophages, and myeloid dendritic cells entered the brain, whereas the situation at day 4 was dominated by microglia, macrophages, lymphatic dendritic cells, and T cells. Postischemic inflammation did not cause secondary tissue damage during the subacute stage of experimental stroke in SH rats. Considering the intrinsic vascular pathology of SH rats, our study validates this strain for further translational research in poststroke inflammation.

Flow cytometric characterization of brain dendritic cell subsets after murine stroke.

BACKGROUND: Sterile inflammation is a substantial element of post-stroke pathophysiology with the determination of autoimmunity versus tolerance being one of its most important aspects. It is believed that this determination is initiated relatively early after stroke onset by clearing macrophages and migratory dendritic cells (DC). However, the phenotypic differentiation of macrophages and DC is intricate particularly in the disease context. Here, we utilized a set of surface markers used in mucosal immunity research to investigate the involvement of macrophages and DC subpopulations in post-stroke inflammation in mice. FINDINGS: Photothrombotic stroke induced a significant increase of lineage (CD3, B220, Ly6G and CD49b) negative CD11b+ cells in the brain primarily consisting of F4/80+ macrophages and, to a lesser extent, F4/80-/CD11c-/CD11b+ monocytes and F4/80-/CD11c+ DC. The latter could be differentiated into the classical migratory DC subpopulations (CD11b+ and CD103+), but no CD4 or CD8+ DC were found. Finally, stroke caused a significant increase of CD11b/CD103 double-positive DC in the affected brain hemisphere. CONCLUSIONS: The surface marker combination used in this study allowed a phenotypic differentiation of macrophages and DC subpopulations after stroke, thus providing an important prerequisite to study post-stroke immunity and tolerance.