Circular RNAs: Novel Biomarkers in Spermatogenesis Defects and Male Infertility

Biomarker-based high-throughput sperm phenotyping: Andrology in the age of precision medicine and agriculture

Reproductive efficiency is crucial for animal agriculture. This economically important aspect can be influenced by environmental burdens, nutritional imbalance, and gonadal or gametic malformations of genetic origin. Successful implementation of genomic-driven selective breeding in cattle depends on the reproductive performance of artificial insemination (AI) sires with valuable genomic production traits. Reproduction is traditionally viewed as a complex set of polygenic traits that are negatively impacted by using a small number of often closely related sires selected for AI due to their superior genetics. Despite recent progress, it remains difficult to define relationships between sire genome and variation in sperm phenotypes, even though several types of heritable, non-compensable sperm defects have been identified. In this review, we discuss the concept of sperm quality biomarker discovery and genomics of male fertility. We also outline a multidisciplinary genome-to-phenome approach for investigating heritable mutations and their impacts on bull fertility, sperm phenotypes and paternal contributions to early pregnancy. High-precision phenotyping requires novel, state-of-the-art instrumentation for sperm quality evaluation and development of new biomarkers of sperm quality in farm animals, with potential for incorporation into andrology-specific machine learning protocols and translation to human andrology. We conclude that reproduction is a complex phenotype that can be deciphered and explored for more precise male fertility evaluation and higher reproductive efficiency.

CDR1as Deficiency Prevents Photoreceptor Degeneration by Regulating miR-7a-5p/α-syn/Parthanatos Pathway in Retinal Detachment

Retinal detachment (RD) is the separation of the neural retina from the retinal pigment epithelium, with photoreceptor degeneration being a major cause of irreversible vision loss. Ischemia and hypoxia after RD decreased the level of miR-7a-5p (miR-7) and promoted the expression of its main target, α-synuclein (α-syn), which activated the parthanatos pathway and led to photoreceptor damage. Circular RNA CDR1as, which is an antisense transcript of cerebellar degeneration-related protein 1, functions as a "sponge" for miR-7, thereby regulating its abundance and activity. In this study, we first reported that CDR1as expression is elevated after RD. Adeno-associated virus serotype 9 vector containing the shRNA-CDR1as sequence was used to inhibit CDR1as expression via subretinal injection. Hematoxylin and eosin staining and transmission electron microscopy revealed that the morphology and outer nuclear layer thickness of the retina were preserved and photoreceptor cell death was decreased after experimental RD in mice. Mechanistically, CDR1as deficiency significantly increased the expression of miR-7, then decreased the expression of α-syn, poly (ADP-ribose) polymerase 1, apoptosis-inducing factor, and migration inhibitory factor. Furthermore, visual function was improved as shown by Morris water maze experiments in the mouse model of RD. Our findings suggest a surprisingly neuroprotective role for CDR1as deficiency, which is probably mediated by enhancing miR-7 activity and inhibiting α-syn/poly (ADP-ribose) polymerase 1/apoptosis-inducing factor pathway, thereby preventing photoreceptor degeneration.

Circular RNAs: novel noncoding players in male infertility

Infertility is a global problem being associated with emotional and financial burden. Recent studies have shown contribution of a group of non-coding RNAs, namely circular RNAs (circRNAs) to the etiology of some infertility conditions. CircRNA are transcribed from exons and form a circular RNA molecule, being abundant in eukaryotes. Traditionally classified as non-coding RNA, these transcripts are endogenously produced through either non-canonical back-splicing or linear splicing, typically produced from precursor messenger ribonucleic acid (pre-mRNA). While during the canonical splicing process the 3' end of the exon is joined to the 5' end of the succeeding exon to form linear mRNA, during backsplicing, the 3' end to the 5' end of the same exon is joined to make a circular molecule. circRNAs are involved in the regulation of several aspects of spermatogenesis. They appear to influence how stem germ cells grow and divide during the sperm production process. Malfunctions in circRNA activity could contribute to male infertility issues stemming from abnormalities in spermatogenesis. In the current review, we highlight the exciting potential of circRNAs as key players in the male fertility.

Unravelling the epigenetic impact: Oxidative stress and its role in male infertility-associated sperm dysfunction

Male infertility is a multifactorial condition influenced by epigenetic regulation, oxidative stress, and mitochondrial dysfunction. Oxidative stress-induced damage leads to epigenetic modifications, disrupting gene expression crucial for spermatogenesis and fertilization. Paternal exposure to oxidative stress induces transgenerational epigenetic alterations, potentially impacting male fertility in offspring. Mitochondrial dysfunction impairs sperm function, while leukocytospermia exacerbates oxidative stress-related sperm dysfunction. Therefore, this review focuses on understanding these mechanisms as vital for developing preventive strategies, including targeting oxidative stress-induced epigenetic changes and implementing lifestyle modifications to prevent male infertility. This study investigates how oxidative stress affects the epigenome and sperm production, function, and fertilization. Unravelling the molecular pathways provides valuable insights that can advance our scientific understanding. Additionally, these findings have clinical implications and can help to address the significant global health issue of male infertility.

Identification of a circRNA-miRNA-mRNA network to explore the effects of circRNAs on Holstein bull testis after sexual maturity

Spermatogenesis is an extremely sophisticated and complex process and is regulated not only by a large number of genes, but also by a large number of epigenetic factors. Although existing studies have demonstrated that circRNAs plays an important regulatory role in spermatogenesis, there is still insufficient information to properly understand the regulatory role and mechanism of circRNA action. We addressed this issue by examining the testes of two Holstein bull developmental stages; three 8-week-olds (young bull, YB) and three 80-week-olds (adult bull, AB), randomly selected from the same breeding stock. A total of 3032 circRNAs, 683 miRNAs were identified as significantly differentially expressed noncoding RNAs, and 14,081 mRNAs. Based on these results, a circRNA-miRNA-mRNA competing endogenous RNA (ceRNA) regulatory network was constructed containing 3298 targeted regulatory axes. Modular analysis revealed a total of four modules in the ceRNA regulatory network. Functional analysis of these results showed that the ceRNA regulatory network in AB testis exhibited more positive regulatory effects on the spermatogenesis cycle checkpoints, chromosome and cytoplasm segregation, sperm tail formation, and sperm motility. In addition, screening combining the results of our previous studies on lncRNA regulation of spermatogenesis revealed 4 genes (FOXO4, PPP1CB, CDC26, and CDKN1B) that co-exist in the 2 ceRNA regulatory networks, lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA. A ceRNA regulatory network was constructed based on these genes. This study demonstrated the possible regulatory role of circRNAs in adult testicular spermatogenesis based on constructed transcriptome profiles and furtzher broadened our understanding of the regulatory role of circRNAs in spermatogenesis.

Seminal plasma biomarkers for predicting successful sperm retrieval in patients with nonobstructive azoospermia: a narrative review of human studies

BACKGROUND

Non-obstructive azoospermia (NOA) is considered to be the most severe form of male infertility. Before the emergence of surgical testicular sperm extraction and assisted reproductive technology, NOA patients could hardly become biological fathers of their children. However, failure of the surgery could cause physical and psychological harm to patients such as testicular damage, pain, hopeless of fertility and additional cost. Therefore, predicting the successful sperm retrieval (SSR) is so important for NOA patients to make their choice whether to do the surgery or not. Because seminal plasma is secreted by the testes and accessory gonads, it can reflect the spermatogenic environment, making it a preferential choice for SSR valuation. The purpose of this paper is to summarize the available evidence and provide the reader with a broad overview of biomarkers in seminal plasma for SSR prediction.

RESULTS

A total of 15,390 studies were searched from PUBMED, EMBASE, CENTRAL and Web of Science, but only 6615 studies were evaluated after duplications were removed. The abstracts of 6513 articles were excluded because they were irrelevant to the topic. The full texts of 102 articles were obtained, with 21 of them being included in this review. The included studies range in quality from medium to high. In the included articles, surgical sperm extraction methods included conventional testicular sperm extraction (TESE) and microdissection testicular sperm extraction (micro-TESE). Currently, the biomarkers in seminal plasma used to predict SSR are primarily RNAs, metabolites, AMH, inhibin B, leptin, survivin, clusterin, LGALS3BP, ESX1, TEX101, TNP1, DAZ, PRM1 and PRM2.

CONCLUSION

The evidence does not conclusively indicate that AMH and INHB in seminal plasma are valuable to predict the SSR. It is worth noting that RNAs, metabolites and other biomarkers in seminal plasma have shown great potential in predicting SSR. However, existing evidence is insufficient to provide clinicians with adequate decision support, and more prospective, large sample size, and multicenter trials are urgently needed.

C-Type Natriuretic Peptide (CNP) Could Improve Sperm Motility and Reproductive Function of Asthenozoospermia

This study is to analyze the effect of C-type natriuretic peptide (CNP) on sperm motility of asthenozoospermia and explore the influence mechanism of CNP on the reproductive system and sperm motility. Our results showed that the concentration of CNP in asthenospermia patients’ semen was lower than in normal people’s. The motility of sperm could be improved markedly by CNP and 8-Br-cGMP, while the effect of CNP was inhibited by NPR-B antagonist and KT5823. In the asthenozoospermia mouse model induced by CTX, CNP injection could improve sperm motility in the epididymis, alleviate tissue damage in the testes and epididymis, and increase testosterone levels. The asthenospermia mouse model showed high activity of MDA and proinflammatory factors (TNF-α, IL-6), as well as low expression of antioxidants (SOD, GSH-Px, CAT) in the testis and epididymis, but this situation could be significantly ameliorated after being treated with CNP. Those studies indicated that the concentration of CNP in the semen of asthenospermia patients is lower than in normal people and could significantly promote sperm motility through the NPR-B/cGMP pathway. In the asthenospermia mouse model induced by CTX, CNP can alleviate the damage of cyclophosphamide to the reproductive system and sperm motility. The mechanism may involve increasing testosterone and reducing ROS and proinflammatory factors to damage the tissue and sperm.

Nomogram based on a circular RNA biomarker for predicting the likelihood of successful sperm retrieval via microdissection testicular sperm extraction in patients with idiopathic non-obstructive azoospermia

BACKGROUND

Many circular RNAs (circRNAs) are specifically expressed in the testes and seminal plasma of patients with non-obstructive azoospermia (NOA), highlighting them as potential predictors of microdissection testicular sperm extraction (micro-TESE) outcomes. Although research has indicated that circular RNA monoglyceride lipase (circ_MGLL) is highly expressed in the testicular tissues of patients with NOA, the association between circ_MGLL expression and sperm retrieval outcomes (SROs) in patients with idiopathic non-obstructive azoospermia (iNOA) receiving micro-TESE remains unclear.

METHODS

This single-center, retrospective cohort study enrolled 114 patients with iNOA who underwent micro-TESE at Northwest Women's and Children's Hospital from January 2017 to November 2021. A logistic regression model was used to examine associations between SRO and circ_MGLL expression in testicular tissues, the results of which were used in conjunction with previous findings to establish a nomogram. The predictive performance of the circ_MGLL-based nomogram was evaluated via calibration curves, receiver operating characteristic curves, and decision curve analysis (DCA) using an internal validation method.

RESULTS

The generalized additive model indicated that the probability of successful SRO for micro-TESE decreased as circ_MGLL expression increased in testicular tissues. Across the entire cohort, univariate logistic regression analysis revealed that circ_MGLL expression was inversely associated with SRO in patients with NOA. This trend did not change after stratification according to age, body mass index, testicular volume, follicle-stimulating hormone (FSH) level, luteinizing hormone (LH) level, testosterone (T) level, or pathological type (or after adjusting for these confounders) (odds ratio <1, P < 0.001). A nomogram was then generated by integrating circ_MGLL, pathological types, and FSH, LH, and T levels. The circ_MGLL-based predictive model achieved satisfactory discrimination, with an area under the curve of 0.857, and the calibration curves demonstrated impressive agreement. The DCA indicated that the net clinical benefit of the circ_MGLL-based predictive model was greater than that of circ_MGLL alone.

CONCLUSION

circ_MGLL is significantly associated with the SRO of micro-TESE in patients with iNOA. The circ_MGLL-based nomogram developed in the current study can predict successful SRO with high accuracy.