Highly specific gene therapy in a rat model of sporadic Alzheimer’s disease: use of adeno‐associated viral vectors to overexpress IGF1 in hippocampal astrocytes

Abstract

AbstractBackgroundSporadic Alzheimer’s disease (sAD) is the most prevalent neurodegenerative disease. The cerebral histopathological study shows that the hippocampus (Hc) is severely affected and presents marked astroglial reactivity and in consequence, neuronal trophic support decreases. We set out to develop an astrocyte‐targeted therapy that prevents the detrimental actions of reactive astrocytes, enhance their neuroprotection, and restore their modulatory properties in our sAD rat model mediated by the intracerebroventricular (icv) injection of streptozotocin (STZ).Method AAV generation: Bicistronic serotype 9 adeno‐associated viruses (AAVs) driven by the gfaABC1D promoter (astrocyte specific) [Lee et al 2008. https://doi.org/10.1002/glia.20622] were generated by the 3‐plasmid system. Two vectors harbouring the cassettes gfaABC1D‐IGF1‐ires‐tdTomato (AAV‐IGF1) and gfaABC1D‐GFP‐ires‐tdTomato (AAV‐GFP) were constructed. AAVs characterization was performed by RT‐qPCR and immunohistochemistry (IHC). Gene therapy in Hc with AAV‐IGF1: Young male rats were used and divided into 3 groups: SHAM, GFP and IGF1. On Experimental Day (ED) ‐28, animals received bilateral injections of artificial cerebrospinal fluid (aCSF) (SHAM) or AAV‐GFP/IGF1(GFP/IGF1). At ED 0, animals received icv aCSF (SHAM) or STZ (GFP/IGF1) (3mg/kg) bilaterally. Among the ED +17/+26 behavioural tests were performed (Open Field Test, Novel Object Recognition Test, and Barnes Maze).ResultTransgenes overexpression was confirmed by RT‐qPCR and IHC. Vectors specificity was determined since 100% of the cells with red fluorescence (tdTomato+) were GFAP+. We also observed that a single injection of the vector is sufficient to transduce Hc throughout its rostro caudal extension. Animals belonging to the AAV‐GFP+STZ group showed a significant deterioration in the behavioural tests, while AAV‐IGF1+STZ animals did not show significant differences compared with the SHAM control in tested behaviours.ConclusionWe explored a targeted therapeutic approach with high specificity to hippocampal astrocytes, which allowed us to modulate astrocyte IGF1 expression, thus promoting neuroprotective effects and preventing behavioural decline in animals with sAD. Consequently, our results are encouraging and suggest that astrocyte manipulation can be approached as a promising therapeutic means.*PCR and JP have equal contribution in this work