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

*PCR and JP have equal contribution in this work. Background: Sporadic Alzheimer’s disease (sAD) is the most prevalent neurodegener-ative disease. The cerebral histopathological study shows that the hippocampus (Hc) isseverely affected and presents marked astroglial reactivity and in consequence, neu-ronal trophic support decreases. We set out to develop an astrocyte-targeted therapythat prevents the detrimental actions of reactive astrocytes, enhance their neuropro-tection, and restore their modulatory properties in our sAD rat model mediated by theintracerebroventricular (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 harbouringthe cassettes gfaABC1D-IGF1-ires-tdTomato (AAV-IGF1) and gfaABC1D-GFP-ires-tdTomato (AAV-GFP) were constructed. AAVs characterization was performed byRT-qPCR and immunohistochemistry (IHC). Gene therapy in Hc with AAV-IGF1: Youngmale rats were used and divided into 3 groups: SHAM, GFP and IGF1. On Experi-mental Day (ED) -28, animals received bilateral injections of artificial cerebrospinalfluid (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 behaviouraltests were performed (Open Field Test, Novel Object Recognition Test, and BarnesMaze).Result: Transgenes overexpression was confirmed by RT-qPCR and IHC. Vectors speci-ficity 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 totransduce Hc throughout its rostro caudal extension. Animals belonging to the AAV-GFP+STZ group showed a significant deterioration in the behavioural tests, whileAAV-IGF1+STZ animals did not show significant differences compared with the SHAMcontrol in tested behaviours. Conclusion: We explored a targeted therapeutic approach with high specificity tohippocampal astrocytes, which allowed us to modulate astrocyte IGF1 expression,thus promoting neuroprotective effects and preventing behavioural decline in ani-mals with sAD. Consequently, our results are encouraging and suggest that astrocytemanipulation can be approached as a promising therapeutic means.