Selective loss of kisspeptin signaling in oocytes causes progressive premature ovulatory failure

Study question: Does direct kisspeptin signaling in the oocyte have a role in the control of follicular dynamics and ovulation?Summary answer: Kisspeptin signaling in the oocyte plays a relevant physiological role in the direct control of ovulation; oocyte-specific ablation of kisspeptin receptor, Gpr54, induces a state of premature ovulatory failure in mice that recapitulates some features of premature ovarian insufficiency (POI).What is known already: Kisspeptins, encoded by the Kiss1 gene, are essential for the control of ovulation and fertility, acting primarily on hypothalamic GnRH neurons to stimulate gonadotropin secretion. However, kisspeptins and their receptor, Gpr54, are also expressed in the ovary of different mammalian species, including humans, where their physiological roles remain contentious and poorly characterized.Study design, size, duration: A novel mouse line with conditional ablation of Gpr54 in oocytes, named OoGpr54-/-, was generated and studied in terms of follicular and ovulatory dynamics at different age-points of postnatal maturation. A total of 59 OoGpr54-/- mice and 47 corresponding controls were analyzed. In addition, direct RNA sequencing was applied to ovarian samples from 8 OoGpr54-/- and 7 control mice at 6 months of age, and gonadotropin priming for ovulatory induction was conducted in mice (N = 7) from both genotypes.Participants/materials, setting, methods: Oocyte-selective ablation of Gpr54 in the oocyte was achieved in vivo by crossing a Gdf9-driven Cre-expressing transgenic mouse line with a Gpr54 LoxP mouse line. The resulting OoGpr54-/- mouse line was subjected to phenotypic, histological, hormonal and molecular analyses at different age-points of postnatal maturation (Day 45, and 2, 4, 6 and 10-11 months of age), in order to characterize the timing of puberty, ovarian follicular dynamics and ovulation, with particular attention to identification of features reminiscent of POI. The molecular signature of ovaries from OoGpr54-/- mice was defined by direct RNA sequencing. Ovulatory responses to gonadotropin priming were also assessed in OoGpr54-/- mice.Main results and the role of chance: Oocyte-specific ablation of Gpr54 caused premature ovulatory failure, with some POI-like features. OoGpr54-/- mice had preserved puberty onset, without signs of hypogonadism. However, already at 2 months of age, 40% of OoGpr54-/- females showed histological features reminiscent of ovarian failure and anovulation. Penetrance of the phenotype progressed with age, with >80% and 100% of OoGpr54-/- females displaying complete ovulatory failure by 6- and 10 months, respectively. This occurred despite unaltered hypothalamic Gpr54 expression and gonadotropin levels. Yet, OoGpr54-/- mice had decreased sex steroid levels. While the RNA signature of OoGpr54-/- ovaries was dominated by the anovulatory state, oocyte-specific ablation of Gpr54 significantly up- or downregulated of a set of 21 genes, including those encoding pituitary adenylate cyclase-activating polypeptide, Wnt-10B, matrix-metalloprotease-12, vitamin A-related factors and calcium-activated chloride channel-2, which might contribute to the POI-like state. Notably, the anovulatory state of young OoGpr54-/- mice could be rescued by gonadotropin priming.Large scale data: N/A. .Limitations, reasons for caution: Conditional ablation of Gpr54 in oocytes unambiguously caused premature ovulatory failure in mice; yet, the ultimate molecular mechanisms for such state of POI can be only inferred on the basis of RNAseq data and need further elucidation, since some of the molecular changes observed in OoGpr54-/- ovaries were secondary to the anovulatory state. Direct translation of mouse findings to human disease should be made with caution since, despite the conserved expression of Kiss1/kisspeptin and Gpr54 in rodents and humans, our mouse model does not recapitulate all features of common forms of POI.Wider implications of the findings: Deregulation of kisspeptin signaling in the oocyte might be an underlying, and previously unnoticed, cause for some forms of POI in women.Study funding/competing interest(s): This work was primarily supported by a grant to M.P. and M.T.-S. from the FiDiPro (Finnish Distinguished Professor) Program of the Academy of Finland. Additional financial support came from grant BFU2017-83934-P (M.T.-S.; Ministerio de Economía y Competitividad, Spain; co-funded with EU funds/FEDER Program), research funds from the IVIRMA International Award in Reproductive Medicine (M.T.-S.), and EFSD Albert Renold Fellowship Programme (S.T.R.). The authors have no conflicts of interest to declare in relation to the contents of this work.</p

Inhibition of left ventricular remodelling preserves chamber systolic function in pressure-overloaded mice

Controversy exists whether the development of left-ventricular hypertrophy (LVH) is a mechanism able to prevent cardiac dysfunction under conditions of pressure overload. In the present study we re-assessed the long-term effects of attenuating LVH by using L- and D-propranolol, which are equally able to inhibit the development of LVH induced by aortic banding. The aortic arch was banded proximal to the left common carotid artery in 71 CD-1 mice that were then assigned randomly to receive L-propranolol, D-propranolol (both 80 mg/kg per day) or vehicle. Concurrently, sham-operated mice were given L-propranolol, D-propranolol or vehicle. LV dimension and performance were evaluated under isoflurane anaesthesia by cine-magnetic resonance imaging, echocardiography and cardiac catheterization up to 8 weeks after surgery. After 2 weeks of pressure overload, the vehicle-treated banded mice had enhanced LV weight, normal chamber size and increased relative wall thickness (concentric hypertrophy), whereas L-propranolol- or D-propranolol-banded mice showed a markedly blunted hypertrophic response, i.e. normal chamber size and normal relative wall thickness, as well as preserved systolic LV chamber function. After 4 weeks, the vehicle-treated banded mice showed LV enlargement with a reduced relative wall thickness (eccentric remodelling) and a clear-cut deterioration in LV systolic function. In contrast, L-propranolol- or D-propranolol-treated banded mice showed normal chamber size with a normal relative wall thickness and preserved systolic function. A distinct histological feature was that in banded mice, L-or D-propranolol attenuated the development of cardiomyocyte hypertrophy but not the attendant myocardial fibrosis. At the 8-week stage, LV dysfunction was present in propranolol-treated banded mice although it was much less severe than in vehicle-treated banded mice. It is concluded that (i) deterioration of LV systolic performance is delayed if LV hypertrophy is inhibited, (ii) banding-induced deterioration of LV systolic function is associated with LV eccentric remodelling and (iii) the antihypertrophic effect of propranolol is due to a selective action on cardiomyocytes rather than on collagen accumulatio