LRRK2 G2019S induces anxiety/depression-like behavior before the onset of motor dysfunction with 5-HT 1A receptor upregulation in mice

Abstract

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of Parkinson’s disease (PD). The neuropathology of LRRK2 mutation-related PD, including increased dopaminergic neurodegeneration and Lewy bodies, is indistinguishable from that of idiopathic PD. The subtle nonmotor phenotypes of LRRK2 mutation-related PD have not been fully evaluated. In the present study, we examined anxiety/depression-like behaviors and accompanying neurochemical changes in differently aged transgenic (Tg) mice expressing human mutant LRRK2 G2019S. Through multiple behavioral tests, including light– dark test, elevated plus maze, sucrose preference test, forced swimming test, and tail-suspension test, we found that anxiety/depression-like behavior appeared in middle-aged (43–52 weeks) Tg mice before the onset of PD-like motor dysfunction. These behavioral tests were performed using both male and female mice, and there were no sex-related differences in behavioral changes in the middle-aged Tg mice. Along with behavioral changes, serotonin levels also significantly declined in the hippocampus of Tg mice. Additionally, increases in the expression of the 5-HT 1A receptor (5-HT 1A R) grew more significant with aging and were detected in the hippocampus, amygdala, and dorsal raphe nucleus. In vitro study using the serotonergic RN46A and hippocampal HT22 cells showed that 5-HT 1A R upregulation was related to enhanced expression of LRRK2 G2019S and was attenuated by the LRRK2 inhibitor LRRK2-IN-1. Wild-type LRRK2 had no significant effect on 5-HT 1A R transcription. The present study provides the first in vivo and in vitro evidence demonstrating abnormal regulation of 5-HT 1A R along with the manifestation of anxiety/depression-like, nonmotor symptom in PD related to LRRK2.