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Osteopontin Attenuates Secondary Neurodegeneration in the Thalamus after Experimental Stroke

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Abstract

Cortical cerebral ischemia elicits neuroinflammation as well as secondary neuronal degeneration in remote areas. Locally distinct and specific secondary neurodegeneration affecting thalamic nuclei connected to cortical areas highlights such processes. Osteopontin (OPN) is a cytokine-like glycoprotein that is excreted in high amounts after cerebral ischemia and exerts various immunomodulatory functions. We here examined putative protective effects of OPN in secondary thalamic degeneration. We subjected male Wistar rats to photothrombosis and subsequently injected OPN or placebo intracerebroventricularly. Immunohistochemical and fluorescence staining was used to detect the extent of neuronal degeneration and microglia activation. Ex vivo autoradiography with radiotracers available for human in vivo PET studies, i.e., cis-4-[18F]Fluor-d-Proline (D-cis-[18F]FPro), and [6-3H]thymidine ([3H]thymidine), confirmed degeneration and proliferation, respectively. We found secondary neurodegeneration in the thalamus characterized by microglial activation and neuronal loss. Neuronal loss was restricted to areas of microglial infiltration. Treatment with OPN significantly decreased neurodegeneration, inflammation and microglial proliferation. Microglia displayed morphological signs of activation without expressing markers of M1 or M2 polarization. D-cis-[18F]FPro-uptake mirrored attenuated degeneration in OPN-treated animals. Notably, [3H]thymidine and BrdU-staining revealed increased stem cell proliferation after treatment with OPN. The data suggest that OPN is able to ameliorate secondary neurodegeneration in thalamic nuclei. These effects can be visualized by radiotracers D-cis-[18F]FPro and [3H]thymidine, opening new vistas for translational studies.

Intracerebroventricular injection of osteopontin attenuates thalamic degeneration after cortical ischemia (pink area). Disruption of thalamocortical connections (blue) and degeneration of thalamic nuclei (encircled) leads to microglia activation. Osteopontin protects from both neurodegeneration and microglia activation as assessed by histological analysis and autoradiograpic studies.

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Correspondence to Michael Schroeter.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in the studies involving animals were in accordance with the ethical standards of the institution at which the studies were conducted.

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Fig. 8
figure 8

Markers of microglial activation are attenuated by OPN treatment. (a) Isolectin B4 (IB4) and Iba1 double-immunofluorescence staining show attenuated microglial activation in the ipsilateral thalamus of OPN-treated animals. (b) Magnified images of IB4/Iba1 staining showing several double positive cells (white arrow heads) in an exemplary placebo-treated animal compared to an OPN-treated animal with sparse overlap. (c) Double immunofluorescence staining of MHC class II/ Ox6 and Iba1 delineating a distinct population of microglia with upregulated MHC II receptors in the ipsilateral thalamus after stroke. Quantification showed a trend towards decreased upregulation in OPN-treated animals. White arrow heads indicate double labeled cells. Scale bar is 100 μm in a, b and close ups in c (lower row) and 500 μm in 4x pictures of entire thalamus in c (upper row). Bar graphs represent mean ± s.e.m. * p < 0.05

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Ladwig, A., Rogall, R., Hucklenbroich, J. et al. Osteopontin Attenuates Secondary Neurodegeneration in the Thalamus after Experimental Stroke. J Neuroimmune Pharmacol 14, 295–311 (2019). https://doi.org/10.1007/s11481-018-9826-1

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  • DOI: https://doi.org/10.1007/s11481-018-9826-1

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