Loss of MeCP2 Causes Urological Dysfunction and Contributes to Death by Kidney Failure in Mouse Models of Rett Syndrome

Abstract

Rett Syndrome (RTT) is a neurodevelopmental disorder characterized by loss of acquired skills during development, autonomic dysfunction, and an increased risk for premature lethality. Clinical experience identified a subset of individuals with RTT that present with urological dysfunction including individuals with frequent urinary tract infections, kidney stones, and urine retention requiring frequent catheterization for bladder voiding. To determine if urologic dysfunction is a feature of RTT, we queried the Rett Syndrome Natural History Study, a repository of clinical data from over 1000 individuals with RTT and found multiple instances of urological dysfunction. We then evaluated urological function in a mouse model of RTT and found an abnormal pattern of micturition. Both male and female mice possessing Mecp2 mutations show a decrease in urine output per micturition event. Furthermore, we identified signs of kidney failure secondary to urethral obstruction. Although genetic strain background significantly affects both survival and penetrance of the urethral obstruction phenotype, survival and penetrance of urethral obstruction do not directly correlate. We have identified an additional phenotype caused by loss of MeCP2, urological dysfunction. Furthermore, we urge caution in the interpretation of survival data as an endpoint in preclinical studies, especially where causes of mortality are poorly characterized.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Micturition is impaired by loss of MeCP2 function.

(A,A’) male Mecp2tm1.1Bird/Y (NULL) and female Mecp2tm1.1Bird/+ (HET) mice showed abnormal micturition patterns with an increase in the number of micturition bouts, (B,B’) despite similar total volume of urine expelled during the test interval. (C,C’) Thus, the average volume voided per bout was decreased in NULL and HET mice relative to their WT littermates. (D,D’) Furthermore the maximum volume voided during the session was also reduced in the NULL and HET mice relative to WT littermates. Male 129B6F1 WT N = 8, NULL = 7; Female 129B6F1 WT = 5, HET = 6. *p<0.05 ANOVA for effect of genotype. ns not significant.

Fig 2. Loss of MeCP2 function contributes to kidney failure in male Mecp2tm1.1Bird/Y mice.

Moribund NULL mice (mori) exhibited evidence of kidney failure compared to normal serum chemistry values in WT or healthy NULL littermates before they become moribund. Moribund NULL mice exhibited (A) normal Na+, (B) increased K+, (C) increased serum osmolarity, (D) decreased bicarbonate, (E) increased creatinine, and (F) increased blood urea nitrogen levels. (WT N≥17, NULL healthy N≥9, NULL moribund N≥7). *p<0.05 versus all other groups determined by ANOVA with Bonferroni post hoc correction for multiple comparisons.

Fig 3. Representative urological pathology of 129B6F1 Mecp2tm1.1Bird/Y mice.

(A-A’) Gross examination of moribund NULL mice revealed severely distended bladders compared to WT littermates. Bladders indicated by black arrows. (B) A plug of seminal coagulum was present within the penile urethra of the moribund NULL mice. (C-C’) Coronal H&E stained sections through the penile urethra showed that this plug occludes the urethra, effectively limiting urine outflow. Occlusion of the urethra is indicated by * in C’. (D-E’) The kidneys exhibited moderate hydronephrosis observable at both the gross level (D-D’), and in coronal H&E stained sections taken through the middle of the kidney (E-E’). Scale bars: A-A’ 1cm, B 5mm, C-C’ 250μm, D-D’ 5mm, E-E’ 2mm.

Fig 4. Strain dependent survival in Mecp2tm1.1Bird/Y mice and penetrance of urethral obstruction.

(A) Survival plots of male Mecp2tm1.1Bird/Y (NULL) mice show premature lethality across all strains tested. FVB NULL mice died significantly earlier than all strains and 129 NULL mice lived significantly longer than 129B6F1 mice. *p<0.05 versus all other strains, and +p<0.05 versus 129B6F1 and FVB as determined by Tarone-Ware statistics from Kaplan-Meier analysis following Bonferroni post hoc correction for multiple comparisons (15 comparisons). (B) Penetrance of urethral obstruction in male moribund NULL mice varied by strain (p<0.001 determined by Chi-Square) with pure strains showing lower penetrance than isogenic F1 strains. (C) Similarly, penetrance of distended bladder while moribund also varied by strain (p<0.001 determined by Chi-Square) and was lower in the pure strains and highest in the isogenic F1 strains. N for each strain is indicated on the respective graphs. Median survival in days is indicated in the key for panel A.