Human-specific mutations in VMAT1 confer functional changes and multi-directional evolution in the regulation of monoamine circuits

Abstract

BackgroundNeurochemicals like serotonin and dopamine play crucial roles in human cognitive and emotional functions. Vesicular monoamine transporter 1 (VMAT1) transports monoamine neurotransmitters, and its variant (136Thr) is associated with various psychopathological symptoms and reduced monoamine uptake relative to 136Ile. We previously showed that two human-specific amino acid substitutions (Glu130Gly and Asn136Thr/Ile) of VMAT1 were subject to positive natural selection. However, the potential functional alterations caused by these substitutions (Glu130Gly and Asn136Thr) remain unclear. To assess functional changes in VMAT1 from an evolutionary perspective, we reconstructed ancestral residues and examined the role of these substitutions in monoamine uptake in vitro using fluorescent false neurotransmitters (FFN), which are newly developed substances used to quantitatively assay VMATs.ResultsImmunoblotting confirmed that all the transfected YFP-VMAT1 variants are properly expressed in HEK293T cells at comparable levels, and no significant difference was seen in the density and the size of vesicles among them. Our fluorescent assays revealed a significant difference in FFN206 uptake among VMAT1 variants: 130Glu/136Asn, 130Glu/136Thr, and 130Gly/136Ile showed significantly higher levels of FFN206 uptake than 130Gly/136Asn and 130Gly/136Thr, indicating that both 130Glu and 136Ile led to increased neurotransmitter uptake, for which 136Thr and 136Asn were comparable by contrast.ConclusionsThese findings suggest that monoamine uptake by VMAT1 initially declined (from 130Glu/136Asn to 130Gly/136Thr) in human evolution, possibly resulting in higher susceptibility to the external environment of our ancestors.

Humanized substitutions of Vmat1 in mice alter amygdala-dependent behaviors associated with the evolution of anxiety

“…These phenotype changes (i.e., a pattern in which Vmat1 Thr exhibits a similar phenotype while Vmat1 Ile differs compared to Vmat1 WT ) are in line with the in silico prediction of differentiated transport function for the mVMAT1 133Ile (Table 1, Fig. 1b) likewise in the hVMAT1 136Ile 16,17 and previous studies demonstrating altered fear/anxiety responses and psychopathological effects of the variant 16,20 .…”

“…Compared to Vmat1 Ile (Vmat1 Thr/Ile and Vmat1 Ile/Ile ) mice, both wildtype and Vmat1 Thr/Thr mice showed similar behavioral phenotypes and have higher levels of anxiety in both solitary (LD, EP, and OF) and social (SI and CSI) environment. This is expected from the molecular evidence that 136Asn and 136Thr are comparable in the level of monoamine uptake, which is lower than that of 136Ile (15). It is noteworthy that the genotypic effect was not observed for fear response of mice (Supplementary Fig.…”

“…1a) and under positive selection in the human lineage (11). Two substitutions (i.e., Glu130Gly and Asn136Thr) occurred in the human lineage after the divergence from the common ancestor of chimpanzees and humans, and these substitutions combined have been shown to decrease the monoamine uptake of VMAT1 (15). On the other hand, the new "hyper-function" allele (i.e.…”

“…Our previous study showed that a new mutation at the 136th amino acid (136Ile) of VMAT1 has emerged relatively recently in the course of human evolution, and that the human-specific polymorphism Thr136Ile has likely been maintained by balancing selection within non-African populations (11). Fluorometric assays additionally demonstrated that these human-specific residues enhance monoamine neurotransmitter uptake, suggesting the tendency of lower monoamine uptake in early hominids (15). The 136Thr, the dominant variant across populations, is known to be marginally associated with psychiatric diseases, such as bipolar disorder, depression and anxiety, as well as with the neuroticism, a personality trait conferring greater risk of psychiatric disease (16)(17)(18).…”

Humanized substitutions of Vmat1 in mice alter amygdala-dependent behaviors associated with the evolution of anxiety

“…Our previous study showed that a new mutation at the 136th amino acid (136Ile) of VMAT1 has emerged relatively recently in the course of human evolution and that the human-specific polymorphism Thr136Ile has likely been maintained by balancing selection within non-African populations ( Sato and Kawata, 2018 ). Fluorometric assays additionally demonstrated that these human-specific residues enhance monoamine neurotransmitter uptake, suggesting the tendency of lower monoamine uptake in early hominids ( Sato et al., 2019 ). The 136Thr, the dominant variant across populations, is known to be marginally associated with psychiatric diseases, such as bipolar disorder, depression, and anxiety, as well as with neuroticism, a personality trait conferring a greater risk of psychiatric disease ( Lohoff et al., 2006 , 2008a ; Vaht et al., 2016 ).…”