The Role of Skeletal Muscle Ryanodine Receptor Type 1 (RYR1) in Uterine Vascular and Myometrial Smooth Muscle Function During Pregnancy

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Background. Mutations in RYR1 encoding the skeletal muscle ryanodine receptor are a common cause of neuromuscular disorders but have also been implicated in a mild bleeding disorder characterised by severe menorrhagia, post-partum and postoperative bleeding. Excessive bleeding suggests a role of RyR1 in vascular smooth muscle function, an observation experimentally tested and corroborated by Lopez et al. (2016) [1].

Hypothesis. The presence of a gain-of-function Ryr1 mutation in pregnancy will lead to enhanced vasorelaxation of vascular smooth muscle cells and altered contractility of myometrium. This will impact on fetal and placental development and influence the length of gestation and parturition.

Methods. Utilizing the Ryr1Y522S/+ mouse model in late-stage pregnancy (gestation day 18.5), vascular smooth muscle function was investigated using wire myography with a pharmacological approach (phenylephrine, carbachol and dantrolene). Myometrial function was studied using video recordings to determine gestation length, isometric tension recordings of spontaneous myometrial contractions and RNAseq to investigate gene expression changes in the pregnant myometrial tissue. Fetal and placental weight measurements were made on gestation day 18.5. Histological techniques were used to study placental morphology.

Results. Paradoxically, uterine artery vasodilatory capacity (logIC50) was reduced in vessels from heterozygous Ryr1Y522S/+ (mixed litter) dams (10-6.597±0.135, n=20) compared to vessels from wildtype (wildtype litter) dams (10-7.275±0.292, n=22), P=0.0457, but was reversed by dantrolene. The frequency of non-pregnant myometrial contractions was greater in Ryr1Y522S/+ tissue (0.0512±0.00389 Hz) compared to wild-type tissue (0.03046±0.00488 Hz), P=0.0046. The duration of non-pregnant myometrial contractions was conversely decreased in heterozygous tissue (22.91±1.416 s) compared to wild-type tissue (45.71±5.106 s), P=0.0014. Gestation length of Ryr1Y522S/+ mouse pregnancies was not statistically different to that of the wild-type mouse (P=0.8452). The Ryr1Y522S/+ mouse had fewer fetuses in a litter (7.364±0.305, n=22) compared to wild-type littermates (8.481±0.223, n=27), P=0.0248, and lower fetal:placental weight ratios (9.36±0.420, n=11) compared to wild-type (10.88±0.2445, n=16), P=0.0132. The RyR1 protein localised to the junctional zone of the placenta (n=10), as confirmed by spongiotrophoblast marker tpbpα [2].

Conclusions. Through these studies we have shown that the maternal Ryr1 Y522S influences uterine artery vasodilation and myometrial contraction, suggesting a physiological role of RyR1 in smooth muscle function, which contributes to fetal-placental growth.
Funders: King’s Health Partners Institute for Women and Children’s Health

[1] Lopez, R. J., Byrne, S., Vukcevic, M., Sekulic-Jablanovic, M., Xu, L., Brink, M., Alamelu, J., Voermans, N., Snoeck, M., Clement, E., et al. (2016). An RYR1 mutation associated with malignant hyperthermia is also associated with bleeding abnormalities, Science Signaling. doi: 10.1126/scisignal.aad9813.
[2] Simmons, D.G., Fortier, A.L. and Cross, J.C. (2007). Diverse subtypes and developmental origins of trophoblast giant cells in the mouse placenta, Developmental Biology, 304(2), pp. 567–578. doi:10.1016/j.ydbio.2007.01.009.
Original languageEnglish
JournalSociety for Reproductive Investigation (SRI)
Publication statusPublished - 16 Mar 2024
EventSociety for Reproductive Investigation (SRI) Annual Meeting 2024 - Vancouver, Canada
Duration: 12 Mar 202416 Mar 2024


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