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AAV delivery of shRNA against IRS1 in GABAergic neurons in rat hippocampus impairs spatial memory in females and male rats

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Abstract

Brain insulin resistance is a major factor leading to impaired cognitive function and it is considered as the onset of Alzheimer´s disease. Insulin resistance is intimately linked to inflammatory conditions, many studies have revealed how pro-inflammatory cytokines lead to insulin resistance, by inhibiting IRS1 function. Thus, the dysfunction of insulin signaling is concomitant with inflammatory biomarkers. However, the specific effect of IRS1 impaired function in otherwise healthy brain has not been dissected out. So, we decided in our study, to study the specific role of IRS1 in the hippocampus, in the absence of comorbidities. To that end, shRNA against rat and human IRS1 was designed and tested in cultured HEK cells to evaluate mRNA levels and specificity. The best candidate sequence was encapsulated in an AAV vector (strain DJ8) under the control of the cytomegalovirus promoter and together with the green fluorescent protein gene as a reporter. AAV-CMV-shIRS1-EGFP and control AAV-CMV-EGFP were inoculated into the dorsal hippocampus of female and male Wistar rats. One month later, animals undertook a battery of behavioral paradigms evaluating spatial and social memory and anxiety. Our results suggest that females displayed increased susceptibility to AAV-shIRS1 in the novel recognition object paradigm; whereas both females and males show impaired performance in the T maze when infected with AAV-shIRS1 compared to control. Anxiety parameters were not affected by AAV-shIRS1 infection. We observed specific fluorescence within the hilum of the dentate gyrus, in immuno-characterized parvalbumin and somatostatin neurons. AAV DJ8 did not enter astrocytes. Intense green fibers were found in the fornix, mammillary bodies, and in the medial septum indicating that hippocampal efferent had been efficiently targeted by the AAV DJ8 infection. We observed that AAV-shIRS1 reduced significantly synaptophysin labeling in hippocampal-septal projections compared to controls. These results support that, small alterations in the insulin/IGF1 pathway in specific hippocampal circuitries can underlie alterations in synaptic plasticity and affect behavior, in the absence of inflammatory conditions

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Acknowledgements

The authors want to thank all the people that generously donated to Crowdfunding Precipita (FECYT) that sponsored ARN, and the economic support from the Association of Alzheimer Families, AFA, Castellon.

Funding

This work has been supported by Plan Propi from Universitat Jaume I UJI-B2018-01 and Conselleria de Educació, Cultura I sport AICO/2015/042 to AMSP. Predoctoral fellowship from Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital ACIF/2016/250 to SSS.

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Contributions

SSS performed the surgeries, conducted the behavioral paradigms, immunofluorescence, and image analysis, and contributed to manuscript writing; ARN generated the shRNA and AAV particles, did the PCR analysis, and contribute to writing of the manuscript; MTB contributed to the immunofluorescence studies; AMSP designed the study and wrote the manuscript.

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Correspondence to Ana María Sánchez-Pérez.

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The authors declare that the manuscript has not been submitted elsewhere. Authors report no conflict of interest.

Ethical approval

The procedures followed the directive 86/609/EEC of the European Community on the protection of animals used for scientific purposes. The experiments were approved by the Ethics Committee of the University Jaume I (scientific procedure 2019/VSC/PEA/0143).

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Sánchez-Sarasúa, S., Ribes-Navarro, A., Beltrán-Bretones, M.T. et al. AAV delivery of shRNA against IRS1 in GABAergic neurons in rat hippocampus impairs spatial memory in females and male rats. Brain Struct Funct 226, 163–178 (2021). https://doi.org/10.1007/s00429-020-02155-x

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  • DOI: https://doi.org/10.1007/s00429-020-02155-x

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