Implication of INSL3, INSL4 and INSL6 in Male Fertility
Development

Hadiselimovic Faruk

Special Article – Male Fertility

Austin Andrology. 2018; 3(2): 1023.

Implication of INSL3, INSL4 and INSL6 in Male Fertility Development

Hadiselimovic Faruk*

Director of Cryptorchidism Research Institute Liestal, Kindermedizinisches Zentrum 4410 Liestal, Switzerland

*Corresponding author: Hadziselimovic Faruk, Director of Cryptorchidism Research Institute Liestal, Kindermedizinisches Zentrum 4410 Liestal, Switzerland

Received: July 24, 2018; Accepted: August 02, 2018; Published: August 09, 2018

Letter to the Editor

The human insulin family members include; insulin-like growth factors I and II (IGF-I and IGFII); relaxins (RLN1 and RLN2); Leydig cell insulin-like peptide (INSL3); early placenta insulin-like peptide (INSL4); and three recently discovered insulin-like hormones, INSL5, INSL6, and RLN3 [1] as well as four relaxin/insulin like family peptide receptors (Table 1).

Table 1: Differential expression of INSL family genes in Ad- (HIR) versus Ad+ (LIR) group and in the GnRHa treated versus untreated group (GnRHa).




  
    Gene ID 
    Name 
    logFC HIR/LIR 
    FDR HIR/LIR 
    logFC GnRHa 
    FDR GnRHa 
  
  
    INSL1/IGF1 
    insulin-like    1 
    n.s.. 
    n.d. 
    -1.51 
    9.5E-08 
  
  
    INSL2/IGF2 
    insulin-like 2
    n.s.. 
    n.s. 
    -n.s. 
    n.s. 
  
  
    INSL3 
    insulin-like 3
    n.s. 
    n.s.. 
    -1.01 
    0.003 
  
  
    INSL4 
    insulin-like    4 
    n.d. 
    n.d. 
    2.31 
    0.007 
  
  
    INSL5 
    insulin-like    5 
    n.d. 
    n.d. 
    n.d. 
    n.d. 
  
  
    INSL6 
    insulin-like 6
    -2.06 
    0.006 
    n.d. 
    n.d. 
  
  
    RFXP1 
    relaxin/insulin-like family    peptide receptor 1
    n.s. 
    n.s. 
    1.06 
    0.002 
  
  
    RFXP2 
    relaxin/insulin-like family    peptide receptor 2
    n.d. 
    n.d. 
    1.38 
    0.046 
  
  
    RFXP3 
    relaxin/insulin-like family    peptide receptor 3
    n.d.
    n.d 
    n.d. 
    n.d. 
  
  
    RFXP4 
    relaxin/insulin-like family    peptide receptor 4
    n.d. 
    n.d. 
    n.d 
    n.d 
  
  
    RLN1 
    relaxin    1 
    n.d. 
    n.d. 
    n.d. 
    n.d. 
  
  
    RLN2 
    relaxin    2 
    n.d. 
    n.d. 
    n.d. 
    n.d. 
  
  
    RLN3 
    relaxin    3 
    n.d. 
    n.d. 
    n.d. 
    n.d.



Table 1: Differential expression of INSL family genes in Ad- (HIR) versus Ad+ (LIR) group and in the GnRHa treated versus untreated group (GnRHa).

INSL3 is a considered to be a key hormone expressed shortly after sex determination and is involved in the regulation of the transabdominal phase of epididymo-testicular descent [2]. Of interest, Insl3 mutant mouse epididymis lacks smooth musculature because of defective α-smooth muscle actin, which results in a high intraabdominal undescended position of the epididymo-testicular unit [3]. Emmen et al. reported that Insl3 is not essential for Wolffian duct growth [4]. Therefore, only a combination of normal testosterone and INSL3 secretion results in complete transabdominal descent of epididymo-testicular unit [5]. Furthermore, observed significant decline in INSL3 gene signaling after GnRH treatment contrast to statement by Ivell at al. [6] that INSL3 is not acutely regulated by the hypothalamic-pituitary-gonadal axis (Table 1).

INSL4 is known to be expressed in the human placenta [1]. Nothing is known about roles for INSL4 and INSL5 in male reproduction and only very little about relaxin-3, which is mostly considered as a brain peptide. Another member of insulin family, INSL6 is highly expressed in post-meiotic germ cells. Insl6 mutant mice show a marked disruption of spermatogenesis with meiotic arrest [7]. To date, however, no specific receptor for human INSL6 has been discovered.

We selected 15 patients with isolated cryptorchidism, based on histological results, and divided them into 2 groups. Seven belonged to the Ad− (lacking Ad spermatogonia) and 8 to the Ad+ (presenting Ad spermatogonia) group. The patients had a median age of 18.5 months (range 8–59 months). Data from Ad− bilateral cryptorchid boys treated with GnRHa (Buserelin) following the first orchidopexy (surgery) (4 patients) were retrieved from randomized study [8]. Initial biopsies revealed no Ad spermatogonia, indicating defective minipuberty (Ad− group). The second testis was managed by orchidopexy and biopsied 6 months after the initial surgery. Thus, results from 21 biopsies were compared. Patients were age and ethnicity matched. RNA sequencing data from two previous studies were used to analyze manually selected INSL family genes [9,10]. The histological analysis of biopsies, workflow from RNA isolation, through to purification, library preparation, sequencing, data analyses, and expression level analysis, has been previously described in detail [9,10]. Determination of differentially expressed genes, statistical analyses and model design were described previously [9,10]. Only genes with at least one read per million, in at least two samples, were included. P values and foldchanges were calculated for the treatment factor and differentially expressed genes were defined as those displaying a false discovery rate (FDR) of less than 0.05. Raw data files are available at the Database of Genotypes and Phenotypes (dbGaP) with the accession number phs001275.v1.p1.

Long term follow-up studies showed that because of impaired mini-puberty, 97% of cryptorchid HIR males were infertile with an average of 9.1 × 10.6 sperm per ejaculate, while 33% out of this group developed azoospermia [11]. If cryptorchid boys with impaired mini-puberty received treatment with a GnRH analogue following orchidopexy, a normal sperm count was achieved in 86% of subjects [12]. Thus, hormonal treatment with GnRHa in early childhood permanently restored fertility and prevented the development of azoospermia [12].

Testes with defective mini-puberty, with lower testosterone levels, and lack of Ad spermatogonia had significant lower RNA levels INSL6 relative to testes with Ad spermatogonia (Table 1). It is possible therefore that differentially expressed INSL6 gene reflect molecular functions involved in the gonocyte-to-Ad spermatogonia transition in humans during mini-puberty.

Surprisingly, GnRHa treatment did not induce increased expression of INSL6 although it induced Ad spermatogonia differentiation [12]. Observed alternative pathway activation with upregulation of INSL4 indicates a novel role for this gene. Thus, INSL4 and RXFP1 as well as RXFP2 indicate new contributors for Ad spermatogonia differentiation and male fertility development. Of notice, IGF1 expression was downregulated after GnRH treatment supporting the idea that GnRHa induce primarily differentiation and not a self-renewal of spermatogonia.

Conclusion

In conclusion, EGR4 and PITX1 controlled by PROK2/CHD7/ FGFR1/SPRY4 genes are responsible for LH deficiency, which in turn affects the germ cell transitional effectors, FGFR3, FGF9, NANOS2, NANOS3, SOHLH1 and SOHLH2 [13,14]. Upon GnRHa treatment, however, alternative pathways are activated, including the LHsecretion orchestrating factors, EGR2, EGR3, TAC1, TAC3, PROP1 and LEP, as well as the gonocyte-to-Ad spermatogonia transition effectors, DMRTC2, T, PAX7, TERT, NRG1, NRG3, RBMY1B, RBMY1E and RBMY1J [13,14] and newly, INSL4, RXFP1 and RXFP2.

References

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Citation: Faruk H. Implication of INSL3, INSL4 and INSL6 in Male Fertility Development. Austin Andrology. 2018; 3(2): 1023.

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