O-208 Maternal spindle transfer restores the developmental competence of in vitro aged oocytes with diminished metabolic activity identified by hyperspectral imaging
Authors: Costa-Borges N , Parra A , Mestres E , Acacio M , Castello C , Seriola A , Ojosnegros S , Calderón G 
Published: June 2023

Abstract

Study question
Can the developmental competence of poor-quality oocytes identified by hyperspectral imaging be restored by maternal spindle transfer?

Summary answer
Maternal spindle transfer can be efficiently assisted by hyperspectral imaging to identify and subsequently repair the developmental competence of poor-quality oocytes.

What is known already
Oocyte cytoplasmic dysfunctions (including, but not limited to the mitochondria) are a major cause for poor embryonic development. Given that maternal spindle transfer (MST) allows the replacement of the entire cytoplasm of an oocyte, it is a promising method for the enhancement of oocyte developmental competence. However, accurate diagnostic tools for oocyte quality assessment are lacking. Recently, a novel hyperspectral imaging approach has been shown to classify oocytes non-invasively based on their metabolic profile, which could assist in the evaluation of oocyte developmental potential prior to MST.

Study design, size, duration
Oocytes were obtained from young female mice and analyzed blindly by hyperspectral imaging either immediately after collection (fresh group, n = 122), after overnight culture (in-vitro aged group, n = 58) or on a group of MST oocytes (n = 36), where the meiotic spindle from in-vitro aged oocytes was transferred into enucleated fresh oocytes. Oocytes were inseminated by ICSI and cultured in-vitro individually. Correlations between the oocyte’s metabolic profiles and rate of development to the blastocyst stage were performed.

Participants/materials, setting, methods
Oocytes were collected from 6-10 weeks-old superovulated B6CBAF1 females. MST was performed in manipulation medium supplemented with cytochalasin B. After enucleation, karyoplasts were exposed to an inactivated Sendai virus solution to promote membrane fusion. ICSI was performed using a Piezo-Drill actuator. Hyperspectral imaging was done in the near-infra-red regime to avoid photoxicity. Image processing was done using dimensionality reduction, which was then feed to an Akaike Information Criterion algorithm to classify the different metabolic subpopulations.

Main results and the role of chance
Fresh oocytes showed metabolic profiles that significantly differed from the profiles of in-vitro aged oocytes, which were characterized by a pronounced diminished metabolic activity. While in the fresh group, 67% of the oocytes developed into expanded blastocysts, none of the in-vitro aged oocytes with low metabolism produced a blastocyst (p &lt; 1x10-05). Interestingly, MST oocytes that were imaged 1h after nuclear reconstruction, showed a restored metabolic spectrum that resembled the profile from fresh non-manipulated controls. This restoration of the metabolic activity was concomitantly associated with an enhancement of developmental competence, with expanded blastocyst rates (63%) comparable to those of fresh non-manipulated controls (p = 0.668). Blastocyst developmental rates of fresh oocytes after hyperspectral imaging were comparable to oocytes from the same cohort that were not imaged and used as controls.

Limitations, reasons for caution
The metabolic profiles obtained from these experimental groups need to be correlated with implantation rates in mouse. The impaired embryo developmental pattern characteristic of poor-quality oocytes may not be exclusively attributed to metabolic deficiencies, so caution must be exerted when generalizing these results to oocytes with other cytoplasmic dysfunctions.

Wider implications of the findings
MST experiments confirm that the developmental decline of these oocytes is primarily attributed to abnormal function of cytoplasmic factors involved in metabolism, while the nuclear genome remains developmentally competent. MST can benefit from hyperspectral imaging to identify oocytes with impaired developmental potential within a cohort.

Trial registration number
not applicable