engleski

Effect of uroguanylin on development of ischemic brain lesion

Stroke is one of the leading causes of mortality and disability in industrialized countries. Since guanylate cyclase (GC) A activation has a neuroprotective effect after ischemic stroke, the aim of this study is to determine if uroguanylin (UGN), an agonist of GC-C, has a similar effect. In this study, middle cerebral artery occlusion (MCAO) was performed on GC-C KO and UGN KO mice and their WT littermates. Before and 24h after MCAO MR images were taken. 48h following MCAO brain slices were isolated and Ca2+ response to UGN stimulation was recorded. Immunohistochemical staining was performed with GC-C, NeuN, and GFAP antibodies. Both groups of WT animals and UGN KO animals exhibit a stronger Ca2+ response to UGN stimulation in astrocytes of the ischemic penumbra in cerebral cortex but not in the unaffected hemisphere. This stronger activation is gone in GC-C KO animals which might lead to development of smaller ischemic lesions in GC-C KO mice compared to their WT littermates (GC-C WT: 111.3±13.8 mm3, n = 5 ; GC-C KO: 71.5±10.6 mm3, n=6, p=0.039). Although mean arterial pressure was significantly higher in GC-C KO mice compared to their WT littermates (GC-C WT: 68.5±1.8 mmHg, GC-C KO: 80.6±3.5 mmHg, n=6, p=0.011), the blood flow measured before and during MCAO did not differ significantly (Flow before MCAO: GC-C WT: 310±8 LDFU (laser Doppler flux unit), n=5 ; GC-C KO: 336±11 LDFU, n=6, p=0.07 ; Flow during MCAO: GC-C WT: 70±6 LDFU, n=5 ; GC-C KO: 70±4 LDFU, n=6, p=0.999), suggesting no effects of the blood pressure on the blood flow during MCAO or size of the stroke lesion. Since GC-C becomes expressed on penumbral astrocytes following ischemia, while in normoxic conditions it is expressed only in cortical neurons, effects of GC-C on intracellular Ca2+ concentration could be due to activation of cGMP-dependent Ca2+ channels in penumbral astrocytes. Stronger activation of the Ca2+- dependent signaling pathway could lead to the development of larger ischemic lesions in GC-C WT compared to GC-C KO animals, possibly through upregulation of Na+/H+ exchanger followed by tissue acidification and neuronal death. Research was funded by the Scientific Centre of Excellence for Basic, Clinical and Translational Neuroscience (project “Experimental and clinical research of hypoxic-ischemic damage in perinatal and adult brain” ; GA KK01.1.1.01.0007 funded by the European Union through the European Regional Development Fund). The work of doctoral student Anja Barić has been fully supported by the “Young researchers' career development project – training of doctoral students” and project BRADISCHEMIA (UIP-2017-05-8082) of the Croatian Science Foundation funded by the European Union from the European Social Fund.

guanylate cyclase-C ; middle cerebral artery occlusion ; MR imaging ; Ca2+ signaling

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