MeCP2 haplodeficiency and early-life stress interaction on anxiety-like behavior in adolescent female mice

Abstract

Background: Early-life stress can leave persistent epigenetic marks that may modulate vulnerability to psychiatric conditions later in life, including anxiety, depression and stress-related disorders. These are complex disorders with both environmental and genetic influences contributing to their etiology. Methyl-CpG Binding Protein 2 (MeCP2) has been attributed a key role in the control of neuronal activity-dependent gene expression and is a master regulator of experience-dependent epigenetic programming. Moreover, mutations in the MECP2 gene are the primary cause of Rett syndrome and, to a lesser extent, of a range of other major neurodevelopmental disorders. Here, we aim to study the interaction of MeCP2 with early-life stress in variables known to be affected by this environmental manipulation, namely anxiety-like behavior and activity of the underlying neural circuits.

Methods: Using Mecp2 heterozygous and wild-type female mice we investigated the effects of the interaction of Mecp2 haplodeficiency with maternal separation later in life, by assessing anxiety-related behaviors and measuring concomitant c-FOS expression in stress- and anxiety-related brain regions of adolescent females. Moreover, arginine vasopressin and corticotropin-releasing hormone neurons of the paraventricular hypothalamic nucleus were analyzed for neuronal activation.

Results: In wild-type mice, maternal separation caused a reduction in anxiety-like behavior and in the activation of the hypothalamic paraventricular nucleus, specifically in corticotropin-releasing hormone-positive cells, after the elevated plus maze. This effect of maternal separation was not observed in Mecp2 heterozygous females that per se show decreased anxiety-like behavior and concomitant decreased paraventricular nuclei activation.

Conclusions: Our data supports that MeCP2 is an essential component of HPA axis reprogramming and underlies the differential response to anxiogenic situations later in life.

Keywords: Arginine-vasopressin; Corticotropin-releasing hormone; Maternal separation; Rett syndrome; c-FOS.

Fig. 1

Young adult Mecp2 heterozygous females show reduced anxiety-like and depressive-like behaviors. WT and Mecp2.het females, both naive and MS groups, were tested in the EPM, OF, and FST to assess anxiety-like and depressive-like behaviors (WT-naive, n = 14; WT-MS, n = 13; Mecp2.het-naive, n = 12; Mecp2.het-MS, n = 18). In the EPM, A no differences were found among groups in the total distance travelled in the maze, but B Mecp2.het females spent significantly longer time in the open arms of the maze as compared to WT littermates. In the open field, C Mecp2.het females showed a reduction in the total distance traveled in the maze, as compared to WT animals, but D no differences were found in the percentage of time spent in center among groups. In the FST, E Mecp2.het females spent significantly less time immobile than their WT littermate controls. EPM, elevated plus maze; FST, forced swim test; Mecp2.het, Mecp2 heterozygous females; MS, maternal separation; OF, open field; WT, wild type; vs, versus. **p < 0.01, ***p < 0.001

Fig. 2

Mecp2 haplodeficiency and maternal separation reduced anxiety-like behavior and neuronal activation in the paraventricular nuclei upon stress. WT and Mecp2.het females, both naive and MS animals, were re-exposed to the EPM now under bright light conditions, a more aversive version (WT-naive, n = 14; WT-MS, n = 13; Mecp2.het-naive, n = 12; Mecp2.het-MS, n = 18). A No differences were found among groups in the total distance travelled in the maze. B Mecp2.het females spent significantly longer time in the open arms of the maze, as compared to WT littermates, an effect further increased by MS. One hour after behavioral testing in the aversive EPM, a subset of the animals was sacrificed for c-FOS immunohistochemistry and quantification (WT-naïve, n = 4; WT-MS, n = 7; Mecp2.het-naïve, n = 5; Mecp2.het-MS, n = 6). C Representative photomicrographs of c-FOS staining in the paraventricular hypothalamic nucleus of WT-naive, C’ Mecp2.het-MS, C” WT-MS, and C”’ Mecp2.het-naive. Quantification of c-FOS-positive neurons in WT and Mecp2.het females, both naive and MS groups, in D Pa, E PV, F BSTLD, G LSV, and H DG. Pa, paraventricular hypothalamic nucleus; PV, paraventricular thalamic nucleus, BSTLD, bed nucleus of stria terminalis lateral division, dorsal part; LSV, lateral septum, ventral part; DG, dentate gyrus of the hippocampus; EPM, elevated plus maze; Mecp2.het, Mecp2 heterozygous females; MS, maternal separation; WT, wild type; vs, versus. *p < 0.05, **p < 0.01, ***p < 0.001

Fig. 3

Mecp2 haplodeficiency and maternal separation reduced the density c-FOS/CRH neuronal population in the paraventricular hypothalamic nucleus. Representative photomicrographs of A c-FOS/CRH and B c-FOS/AVP double immunofluorescence in the paraventricular hypothalamic nucleus (WT-naïve, n = 4; WT-MS, n = 7; Mecp2.het-naïve, n = 5; Mecp2.het-MS, n = 6). The number of c-FOS-positive cells that colocalize with CRH neurons was significantly reduced in Mecp2.het females and upon maternal separation. Quantification of the number of c-FOS neurons that colocalize with C CRH or D AVP. AVP, arginine vasopressin; c-FOS, FOS proto-oncogene; CRH, corticotropin-releasing hormone; Mecp2.het, Mecp2 heterozygous females; MS, maternal separation; WT, wild type; vs, versus. *p < 0.05; **p < 0.01