# Metabolomics Reveals Abnormal Citrate Cycle and Phenylalanine Metabolism in Testes from Infertile Hybrid Dzo

## TL;DR

This study finds that testicular metabolic issues in dzo hybrids are linked to male infertility, pointing to problems in the citrate cycle and phenylalanine metabolism.

## Contribution

The study identifies testis-specific metabolic disruptions in dzo hybrids as a novel mechanism for hybrid male sterility.

## Key findings

- Testis-specific abnormalities in the citrate cycle and phenylalanine metabolism are linked to dzo male infertility.
- Genes encoding α-ketoglutarate-dependent oxygenases are dysregulated in dzo testes.
- Downregulation of LDHC in dzo testes correlates with reduced phenyllactate levels.

## Abstract

Dzo is a prime example of hybrid male sterility (HMS) in bovines, holding significant theoretical importance in terms of analyzing the mechanisms of interspecific reproductive isolation and speciation. This study revealed that testis-specific abnormalities in the citrate cycle and phenylalanine metabolism are closely associated with dzo male infertility. This research provides comprehensive insights into the citrate cycle as a key pathway linked to dzo sterility, uncovering potential mitochondrial–nuclear incompatibilities that contribute to this HMS phenomenon.

This study investigated the metabolomic profiles and molecular basis of hybrid male sterility (HMS) in dzo (the male F1 hybrid offspring of taurine cattle (Bos taurus, ♂) × domestic yak (Bos grunniens, ♀)). In total, 147 co-different metabolites were identified between liver and testis tissues. Metabolomics analysis linked testis-specific abnormal citrate cycle and phenylalanine metabolism to dzo male infertility. Specifically, α-ketoglutaric acid, L-malic acid, and succinic acid were specific elevated in dzo testes, but not significantly different in liver. The testis-specific metabolite phenyllactate was reduced in dzo. Moreover, genes encoding α-ketoglutarate-dependent oxygenases were dysregulated only in dzo testes, including histone demethylations and RNA m6A modifications. Reactive oxygen species and m6A content were significantly decreased in dzo testes. Multiomics data showed that testis-specific metabolic abnormalities in dzo were linked to upregulated IDH3A and IDH3G, and downregulated testis-specific OGDHL and PDHA2. MiRNA-15b targeting to IDH3A was downregulated in dzo testes. The promoter of PDHA2 was hypermethylated and showed lower chromatin accessibility in dzo testes. Notably, testis-specific LDHC downregulation was also associated with lower phenyllactate in dzo testes, which could be an outcome of male infertility. Overall, this study provides comprehensive insights into the citrate cycle as a key pathway associated with dzo sterility, shedding light on the potential mitochondrial–nuclear incompatibility pertinent to addressing this HMS challenge.