Metabolic and behavioral alterations associated with viral vector-mediated toxicity in the paraventricular hypothalamic nucleus

OBJECTIVE: Combining adeno-associated virus (AAV)-mediated expression of Cre recombinase with genetically modified floxed animals is a powerful approach for assaying the functional role of genes in regulating behavior and metabolism. Extensive research in diverse cell types and tissues using AAV-Cre exemplifies advantages over crossing with Cre driver lines in several aspects, including saving time and avoiding developmental/compensatory issues. We initially sought to study the impact of ablation of corticotropin-releasing hormone (CRH) in the paraventricular hypothalamic nucleus (PVN) using intracranial AAV8-hSyn-Cre injection in adult animals. METHODS: In this study, we stereotactically injected AAV8-hSyn-Cre or a control viral vector (1E13 and 1E12 vg/ml, respectively, both at 150 nL) in both Crh-floxed and wild-type mouse PVN to assess behavioral and metabolic impacts. We then used immunohistochemical markers to systematically evaluate the density of hypothalamic peptidergic neurons and glial cells. RESULTS: We found that delivery of one preparation of AAV8-hSyn-Cre in the PVN led to the development of obesity, hyperphagia, and anxiety-like behaviors. This effect occurred independent of sex and in both floxed and wild-type mice. We subsequently found that AAV8-hSyn-Cre led to neuronal cell death and gliosis at the site of viral vector injections. These behavioral and metabolic deficits were dependent on injection into the PVN specifically. CONCLUSIONS: Our findings reveal that delivery of AAV8-hSyn-Cre could lead to cellular toxicity and lesions in the PVN that cause robust metabolic and behavioral impacts. These alterations can complicate the interpretation of AAV-Cre-mediated gene knockout and highlight the need for rigorous controls.