P-085 Transcriptomic and proteomic characterization of unexplained male infertility: alterations in energy metabolism
Authors: Odriozola A , Urizar-Arenaza I , Navarro B , Muñoa-Hoyos I , Zabala-Goikoetxea M , Araolaza M , Subirán N 
Published: July 2024

Abstract

Study question
Which are the transcriptomic and proteomic profiles of spermatozoa belonging to patients with Unexplained Male Infertility (UMI)?

Summary answer
Transcriptomic and proteomic profiles of UMI patients differ from the fertile men, having the energy metabolism altered.

What is known already
About 30% of infertile couples suffer from “Unexplained Infertility” (UI). Considering that the male factor contributes to 50% of infertility cases, it is estimated that half of all couple UI cases are due to unexplained male infertility (UMI). Men are diagnosed with UMI when despite having “normal” seminal parameters they are unable to conceive. Due to the lack of UMI classification criteria and the seminogram-only-based infertility diagnosis, little is known about the mechanisms underlying UMI.

Study design, size, duration
80 normozoospermic human semen samples with proven fertility and 80 samples from patients with UMI were used for this study. Ejaculates were obtained from Clínica Quirón Bilbao between 2012 and 2018, and after capacitation they were pooled to perform protein and RNA extractions.

Participants/materials, setting, methods
For transcriptomic analysis, libraries were prepared using the SMARTer Stranded Total RNA-Seq Kit v3. Sequencing was performed on NextSeq 2000 system (1x 50 bp, 50 cycles, P3 kit) at Centre de Regulació Genómica (CRG). For the proteomic analysis, Tandem MassTag (TMT) 6-plex isotopic labeling strategy was adopted, and generated peptides were run in a Q Exactive mass spectrometer. To find differentially expressed genes and proteins between both groups EdgeR and Perseus softwares were employed.

Main results and the role of chance
In the present study, a total of 156.124 transcripts and 1722 proteins were identified in human sperm. Principal Component Analysis (PCA) confirmed the existence of distinguishable differences in the transcriptomic and proteomic profile of control and UMI samples. Specifically, 3112 differentially expressed transcripts and 385 differentially expressed proteins were identified. Among the differentially expressed proteins, 49 were correlated with RNA expression. Coherent RNA-protein signatures were mainly related to axonemal dynein complex assembly and flagellated sperm motility. Proteins involved in energy metabolism were enriched in UMI protein signatures but were not well correlated with the RNA. Furthermore, genes involved in protein transport and chromosome condensation were highly enriched in UMI group but were not detected by proteomics profiling. According to our results, there is a lack of RNA-protein correlation at human sperm. However, differential transcriptomic and proteomic profiles were found when comparing fertile normozoospermic samples to UMI samples. Concretely, our results suggest that altered energy metabolism may be one of the key factors in patients leading with UMI. Thus, the study of human sperm metabolism may be essential to find new targets of male infertility.

Limitations, reasons for caution
The lack of a consensus on the classification criteria of UMI makes this group of patients very heterogeneous. Further studies are needed to identify and validate specific transcripts and/or proteins that may alter specific metabolic processes and cause infertility.

Wider implications of the findings
The study of human sperm metabolism may be essential to understand the causes of many UMI cases. In this context, the identification of key protein or transcripts could be very helpful to predict the success of the assisted reproductive treatments.

Trial registration number
Not applicable