P-543 Higher maternal age alters the insulin/IGF system and intracellular lipid metabolism of the endometrium and in the preimplantation embryo – insights from the rabbit model.
Authors: Schindler M , Thoma J , Buske M , De Nivelle J , Toto Nienguesso A , Navarrete Santos A 
Published: June 2023

Abstract

Study question
Our aim was to analyse the embryo-maternal-interaction, focusing on the insulin/IGF-system and lipid metabolism on day 6 of pregnancy in reproductive young and old rabbits.

Summary answer
Advanced maternal age has a decisive effect on maternal and embryonic insulin/IGF-signalling and lipid metabolism, leading to higher embryo loss already during preimplantation period.

What is known already
The reproductive potential in women declines with age. Molecular and biochemical mechanisms involved in age-related infertility and their impact on embryo-maternal-interaction during early pregnancy are still not completely understood. However, establishment of a successful pregnancy depends on the physiological condition of the mother and a continuous dialogue with the developing embryo. The insulin/IGF-system plays a pivotal role in this embryo-maternal crosstalk, connecting maternal insulin/IGF with embryonic metabolism, cell proliferation and differentiation.

Study design, size, duration
We used the rabbit as reproductive model to investigate maternal age-related alterations in embryo-maternal-interaction during preimplantation period. Compared to humans, the rabbit shares high similarities in early embryo development, gastrulation and lipid metabolism (DOI: 10.1530/REP-12-0091 and DOI: 10.1093/ajcn/62.2.458S). A total of 50 young (16-20 weeks) and 31 old (&lt;108 weeks) sexually mature, female rabbits were used for analysis at day 6 post coitum.

Participants/materials, setting, methods
We measured mRNA and protein levels of target genes of the insulin/IGF system and lipid metabolism by quantitative PCR, Western Blot and ELISA. Therefore, maternal blood, endometrium and blastocysts were analysed from reproductive young (16 to 20 weeks) and old (over 108 weeks) rabbits on day 6 of pregnancy. Blastocysts and ovulation points were counted and only blastocysts at the pre-gastrulating stage 1, separated in embryoblast (EB) and trophoblast (TB), were used for further analyses.

Main results and the role of chance
At day 6 of pregnancy, reproductive old rabbits had a lower amount of embryos. Maternal serum insulin and IGF levels were reduced in reproductive old rabbits, accompanied by a paracrine upregulation of IGF1 and its receptors in the endometrium. Preimplantation blastocysts adapted to hormonal changes by reducing IGF1 and IGF2 levels in both embryonic compartments, EB and TB, while the expression of embryonic IGF receptors was unchanged.
Furthermore, an increase of fatty acids metabolism was observed in the ageing endometrium, indicated by the higher level of carnitine palmitoyltransferase I B (CPT1B) and elevated expression of fatty acid binding and transport proteins. These results are in line with lower level of fatty acid synthesis (FASN) in the endometrium from old, gravid rabbits, the key enzyme of fatty acid synthesis. Embryonic fatty acid uptake and b-oxidation were increased in EB and TB, too. The observed changes in embryonic and maternal lipid metabolism are caused by the alterations of the transcription factors cAMP-responsive element binding protein (CREB) and peroxisome proliferator-activated receptor (PPAR) α and γ in endometrium and embryos from reproductive old rabbits.

Limitations, reasons for caution
Rabbit embryogenesis reflects human development only during blastocysts formation. Therefore, statements are limited to the embryogenesis stages investigated.

Wider implications of the findings
The results of the current study are in accordance with the common literature, showing that advanced maternal age affects developmental competence of embryos. Our study points out that advanced maternal age alters lipid metabolism and insulin/IGF-signalling, which are two crucial components in embryo-maternal-interaction.

Trial registration number
not applicable