Testosterone-Dependent miR-26a-5p and let-7g-5p Act as Signaling Mediators to Regulate Sperm Apoptosis via Targeting PTEN and PMAIP1

Abstract

Recent evidence suggests that testosterone deficiency can dramatically decrease the quality of sperm. MicroRNAs (miRNAs) are conserved mediators of post-transcriptional gene regulation in eukaryotes. However, the systemic regulation and function of miRNAs in sperm quality decline induced by testosterone deficiency has not been investigated. Here, we found that the sperm apoptosis was significantly enhanced and the sperm motility was dramatically decreased in hemicastrated pigs. We then used small RNA sequencing to detect miRNA profiles of sperm from pigs with prepubertal hemicastration (HC) and compared them with control libraries. We identified 16 differentially expressed (DE) miRNAs between the sperm of prepubertal HC and control (CT) pigs. Functional enrichment analysis indicated that the target genes of these DE miRNAs were mainly enriched in apoptosis-related pathways including the p53, mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR) pathways. Furthermore, gain- and loss-of-function analyses demonstrated potential anti-apoptotic effects of the DE miRNAs miR-26a-5p and let-7g-5p on sperm cells. The luciferase reporter assay confirmed that PTEN and PMAIP1 are targets of miR-26a-5p and let-7g-5p, respectively. Spearman’s correlation analysis revealed significantly positive correlations between the sperm and its corresponding seminal plasma exosomes regarding the miRNA expression levels. In conclusion, testosterone deficiency-induced changes in the miRNA components of seminal plasma exosomes secreted by the genital tract may partially elucidate sperm miRNAome alterations, which are further responsible for the decline of sperm motility.

Keywords: apoptosis; exosome; miRNA; sperm motility; testosterone deficiency.

Figure 1

Altered profile of biological parameters between prepubertal hemicastration and control pigs. The influences of prepubertal hemicastration on porcine (A) body weight, (B) body size, and (C) main organ indexes. Prepubertal hemicastration significantly affected the (D) serum testosterone level, (E) testis index, and (F) testis size. (G) Histological analysis of the testis of control and hemicastrated pigs. Bars = 200 μm; 100× magnification; hematoxylin-eosin staining. (H) Sperm density of experimental pigs. (I) Sperm motility rate (%) represents the percentage of sperm showing motility. (J) Three motility parameters, including the curvilinear velocity (VCL, μm/s), average path velocity (VAP, μm/s) and straight line velocity (VSL, μm/s), were assessed for both experimental pig groups. (K) Amplitude of lateral head displacement (ALH, μm) for both experimental pig groups. (L) The wobble (WOB, %) measures the oscillation of the actual trajectory of sperm cells. (M,N) Sperm apoptosis rates of control and hemicastrated pigs were evaluated by flow cytometry analysis. (O) Apoptotic bodies in testicular tissues of control and hemicastrated pigs, detected as strongly green fluorescent cells. Bars = 100 μm; 200× magnification. CT and HC represent the prepubertally hemicastrated Yorkshire boars and normal controls, respectively. All data are expressed as means ± SD. * p < 0.05, ** p < 0.01.

Figure 1

Altered profile of biological parameters between prepubertal hemicastration and control pigs. The influences of prepubertal hemicastration on porcine (A) body weight, (B) body size, and (C) main organ indexes. Prepubertal hemicastration significantly affected the (D) serum testosterone level, (E) testis index, and (F) testis size. (G) Histological analysis of the testis of control and hemicastrated pigs. Bars = 200 μm; 100× magnification; hematoxylin-eosin staining. (H) Sperm density of experimental pigs. (I) Sperm motility rate (%) represents the percentage of sperm showing motility. (J) Three motility parameters, including the curvilinear velocity (VCL, μm/s), average path velocity (VAP, μm/s) and straight line velocity (VSL, μm/s), were assessed for both experimental pig groups. (K) Amplitude of lateral head displacement (ALH, μm) for both experimental pig groups. (L) The wobble (WOB, %) measures the oscillation of the actual trajectory of sperm cells. (M,N) Sperm apoptosis rates of control and hemicastrated pigs were evaluated by flow cytometry analysis. (O) Apoptotic bodies in testicular tissues of control and hemicastrated pigs, detected as strongly green fluorescent cells. Bars = 100 μm; 200× magnification. CT and HC represent the prepubertally hemicastrated Yorkshire boars and normal controls, respectively. All data are expressed as means ± SD. * p < 0.05, ** p < 0.01.

Figure 2

miRNA expression profiles of sperm cells in control and hemicastrated pigs. (A) The length distribution of identified miRNAs in all small RNA libraries. (B) Hierarchical clustering analysis for the expression of 206 known sperm miRNAs between control and hemicastrated pigs based on the Euclidean distance. Complete linkage hierarchic clustering was performed with the Euclidian distance measure. (C) Ranking analysis of the top 10 sperm miRNAs with the highest expression levels in control and hemicastrated pigs. The labels upper the bar represent the ranking of the top 10 miRNAs by expression, while the labels below the bar represent the accumulative % of the top 10 miRNAs in total read per million (RPM) of all expressed miRNAs. Seven miRNAs that are present in the top 10 position in both experimental groups are connected by lines. (D) Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of potential targets of the DE miRNAs. p-Values indicating the significance of enrichment were calculated by the Benjamini-corrected modified Fisher’s exact test. (E) Heat maps of the expression pattern of the DE sperm miRNA families and a cluster in control and hemicastrated groups. CT and HC represent prepubertally hemicastrated Yorkshire boars and controls, respectively.

Figure 2

miRNA expression profiles of sperm cells in control and hemicastrated pigs. (A) The length distribution of identified miRNAs in all small RNA libraries. (B) Hierarchical clustering analysis for the expression of 206 known sperm miRNAs between control and hemicastrated pigs based on the Euclidean distance. Complete linkage hierarchic clustering was performed with the Euclidian distance measure. (C) Ranking analysis of the top 10 sperm miRNAs with the highest expression levels in control and hemicastrated pigs. The labels upper the bar represent the ranking of the top 10 miRNAs by expression, while the labels below the bar represent the accumulative % of the top 10 miRNAs in total read per million (RPM) of all expressed miRNAs. Seven miRNAs that are present in the top 10 position in both experimental groups are connected by lines. (D) Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of potential targets of the DE miRNAs. p-Values indicating the significance of enrichment were calculated by the Benjamini-corrected modified Fisher’s exact test. (E) Heat maps of the expression pattern of the DE sperm miRNA families and a cluster in control and hemicastrated groups. CT and HC represent prepubertally hemicastrated Yorkshire boars and controls, respectively.

Figure 3

The miR-26a-5p-mediated regulation of sperm quality. (A) Relative expression levels of miR-26a-5p in control, mimic- and inhibitor-transfected sperm. (B) Effect of miR-26a-5p mimic and inhibitor on three velocity parameters of sperm cells, including curvilinear velocity (VCL, μm/s), average path velocity (VAP, μm/s) and straight line velocity (VSL, μm/s). (C) Effect of miR-26a-5p mimics and inhibitor on sperm motility rate (%). No significant changes were observed in (D) amplitude of lateral head displacement (ALH, μm), (E) sperm density (million/mL), (F) motility parameter wobble (WOB, %), or (G) linearity (LIN, %) and STR (%). (H) Effect of miR-26a-5p mimics and inhibitor on the expression levels of apoptosis-related genes. Con, control; Mimi, mimics; MC, mimic control; Inhi, inhibitor; IC, inhibitor control. CT and HC represent prepubertally hemicastrated Yorkshire boars and normal controls, respectively. Three independent experiments were performed in triplicate and all data are expressed as means ± SD. * p < 0.05, ** p < 0.01.

Figure 4

Testosterone-dependent miRNAs exert a pro-viability function by inhibiting pro-apoptotic factors. (A) Potential binding sites predicted by TargetScan [40] and RNAhybrid [41] for miR-26a-5p and let-7g-5p in the 3′-UTR of PTEN and the 5′-UTR of PMAIP1, respectively, and the mutant PTEN 3′-UTR and PMAIP1 5′-UTR used in our study. A luciferase reporter assay was performed by co-transfecting luciferase reporter containing the 3′-UTR of PTEN and 5′-UTR of PMAIP1 (wild-type (Wt) or mutant (Mut)) with the mimic or control of miR-26a-5p and let-7g-5p into PK15 cells. The red underlined bases highlighted the miRNA seed sequences and their corresponding target sites in the mRNA UTR sequences. Luciferase activity was determined 48 h after transfection for (B) miR-26a-5p and (C) let-7g-5p. MC, mimics control. Three independent experiments were performed in triplicate and all data are expressed as means ± SD. ** p < 0.01.

Figure 5

The comparison of miRNA data of sperm and seminal plasma exosomes. (A) Particle size distribution of CT-1 seminal plasma exosomes detected using atomic force microscopy. (B) Western blot analysis showing the enrichment of CD63 and CD81 and the absence of tubulin in CT-1 seminal plasma exosomes compared with sperm cell lysates. (C) The expression pattern of a sperm-specific marker, PRM-1/2, in sperm and seminal plasma exosomes. (D) Hierarchical clustering analysis for the expression of known exosomal miRNAs between control and hemicastrated pigs based on the Euclidean distance. (E) Spearman’s correlation of miRNA expression profiles between sperm and corresponding seminal plasma exosomes. (F) Venn diagram of DE miRNAs between sperm and seminal plasma exosomes in the HC versus CT group. (G) qRT-PCR validation of expression changes of five overlapping DE miRNAs between HC and CT groups. Three independent qRT-PCR experiments were performed in triplicate. All data are expressed as means ± SD. ** p < 0.01.