Expression of the Insulin-Like Peptide 3 (INSL3) Hormone-Receptor (LGR8) System in the Testis1

Partial cDNA sequence of a relaxin-like factor (RLF) receptor, LGR8 and possible existence of the RLF ligand-receptor system in goat testes

Relaxin-like factor (RLF), also known as insulin-like factor 3 (INSL3), is produced by testicular Leydig cells, but its specific receptor LGR8 (leucine-rich repeat family of G-protein-coupled receptor 8) has not been identified in goats. This study aimed to identify complementary DNA (cDNA) sequences of goat LGR8, and characterize the expression of both RLF and LGR8 in goat testes by RT-PCR and immunohistochemistry. Testes were collected from immature (3-month-old) and mature (24-month-old) Saanen goats, and partial cDNA sequences of the goat homologue of human LGR8 were identified. The sequence encoded a reduced peptide sequence of 167 amino acids, which corresponded to transmembrane regions 2 through 5, followed by the beginning of intracellular loop 3 of human LGR8. Expression of both LGR8 and RLF genes was drastically increased in mature testes compared with immature ones. Although RLF protein was restricted to Leydig cells, LGR8 protein was detected in both Leydig cells and seminiferous epithelial cells (possibly germ cells and Sertoli cells). These results reveal a possible existence of the RLF-LGR8 ligand-receptor system within the goat testis, suggesting that RLF may play a role in testicular function through LGR8 on Leydig cells and seminiferous epithelial cells in an autocrine and/or paracrine manner.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Membrane receptors: structure and function of the relaxin family peptide receptors

The receptors for members of the relaxin peptide family have only recently been discovered and are G-protein-coupled receptors (GPCRs). Relaxin and insulin-like peptide 3 (INSL3) interact with the leucine-rich-repeat-containing GPCRs (LGRs) LGR7 and LGR8, respectively. These receptors show closest similarity to the glycoprotein hormone receptors and contain large ectodomains with 10 leucine-rich repeats (LRRs) but are unique members of the LGR family (class C) as they have an LDL class A (LDLa) module at their N-terminus. In contrast, relaxin-3 and INSL5 interact with another class of type I GPCRs which lack a large ectodomain, the peptide receptors GPCR135 and GPCR142, respectively. These receptors are now classified as relaxin family peptide (RXFP) receptors, RXFP1 (LGR7), RXFP2 (LGR8), RXFP3 (GPCR135) and RXFP4 (GPCR142). This review outlines the identification of the peptides and receptors, their expression profiles and physiological roles and the functional interactions of the peptides with their unique receptors.

Age-related changes in the expression of 11beta-hydroxysteroid dehydrogenase type 2 in rat Leydig cells

Previous studies in rats have shown that the ability of Leydig cells (LCs) to produce testosterone significantly declines with age. To address the possible mechanisms by which aging LCs lose their steroidogenic function, we determined the effect of aging on the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2. The enzyme plays a protective role in blunting the suppressive effects of glucocorticoids on LCs steroidogenesis. Our immunohistochemical analysis revealed progressive decline in 11beta-HDS type 2 expression in LCs of the 18 months of age rats and the most significant reduction in 11beta-HSD2 immunoreactivity was evident in the testicular interstitium of 24- month-old rats. The decrease in the 11beta-HDS type 2 immunostaining in LCs during aging coincided with decline in insulin-like 3/relaxin-like factor (INSL3/RLF) expression, an independent marker for LCs differentiation status. Concomitant with the age-related decrease of 11beta-HDS type 2 immunoreactivity in the LCs population, the immunoexpression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), marker for LCs steroidogenic activity, was greatly reduced at 24 months compared to 3-month-old control. Similar pattern of expression exhibited also androgen receptor (AR) which is localized in the nuclei of Sertoli cells (SCs), LCs, and peritubular cells. During ages we observed progressive decrease in the immunoreactivity for AR in the testicular types and there was a loss of stage specificity in SCs at age of 24 months. It now seems evident that a variety of factors are likely to be involved in age-related decreases in LCs steroidogenesis, including 11beta-HSD type 2. The observed reduction in 11beta-HSD type 2 expression in aging LCs reflects the decline in their protection ability, opposing the suppressive effect of glucocorticoids on testosterone production.

An insight into testis and gubernaculum dynamics of INSL3 - RXFP2 signalling during testicular descent in the dog

Insulin-like 3 (INSL3) plays a prominent role in male development and is supposed to induce the growth of the gubernaculum testis (g.t.), thus being directly involved in testicular descent in humans and rodents. This happens through activation of the RXFP2 receptor (GREAT or LGR8). The INSL3–RXFP2 complex is reputed to play an additional paracrine role in the testis, possibly acting as part of an autocrine feedback loop. The present work provides evidence of the immunolocalisation of INSL3 in the Leydig cells of canine fetuses and of the expression of RXFP2 receptor in different tissues of the g.t. of the same specimens. RXFP2 was localised at the cell membrane of g.t. muscle and connective cells, as well as in the epithelial cells of the developing excurrent ducts. Notably, RXFP2 immunoreactivity of the g.t. was limited to fetuses at ~35–45 days of gestation, which is also the fetal period when the endocrine compartment of the dog testis is active endocrinologically, as confirmed by the anti-P450c17 and anti-INSL3 immunoreactivities of the fetal Leydig cells, and by anti-Müllerian hormone immunoreactivity of the Sertoli cells. The same immunoreactivities were also evaluated in the testes of cryptorchid dogs of different ages. RXFP2 immunoreactivity was absent from genital tracts of cryptorchid testes and g.t. remnants.

Expression and function of G-protein-coupled receptorsin the male reproductive tract

This review focuses on the expression and function of muscarinic acetylcholine receptors (mAChRs), α1-adrenoceptors and relaxin receptors in the male reproductive tract. The localization and differential expression of mAChR and α1-adrenoceptor subtypes in specific compartments of the efferent ductules, epididymis, vas deferens, seminal vesicle and prostate of various species indicate a role for these receptors in the modulation of luminal fluid composition and smooth muscle contraction, including effects on male fertility. Furthermore, the activation of mAChRs induces transactivation of the epidermal growth factor receptor (EGFR) and the Sertoli cell proliferation. The relaxin receptors are present in the testis, RXFP1 in elongated spermatids and Sertoli cells from rat, and RXFP2 in Leydig and germ cells from rat and human, suggesting a role for these receptors in the spermatogenic process. The localization of both receptors in the apical portion of epithelial cells and smooth muscle layers of the vas deferens suggests an involvement of these receptors in the contraction and regulation of secretion.

Fetal Leydig cell origin and development

Male sexual differentiation is a complex process requiring the hormone-producing function of somatic cells in the gonad, including Sertoli cells and fetal Leydig cells (FLCs). FLCs are essential for virilization of the male embryo, but despite their crucial function, relatively little is known about their origins or development. Adult Leydig cells (ALCs), which arise at puberty, have been studied extensively and much of what has been learned about this cell population has been extrapolated to FLCs. This approach is problematic in that prevailing dogma in the field asserts that these 2 populations are distinct in origin. As such, it is imprudent to assume that FLCs arise and develop in a similar manner to ALCs. This review provides a critical assessment of studies performed on FLC populations, rather than those extrapolated from ALC studies to assemble a model for FLC origins and development. Furthermore, we underscore the need for conclusive identification of the source population of fetal Leydig cells.

Relaxin and related peptides in male reproduction

The relaxin hormone is renowned for its function in pregnancy, parturition and other aspects of female reproduction. At the same time, the role of relaxin in male reproduction is still debated. Relaxin is prominently expressed in prostate and its receptors are found in several male reproductive organs; however, the data indicative of its contribution to differentiation and functioning of prostate or testis are contradictory. Prostate relaxin is a main source of this peptide in the seminal plasma. The relaxin effects on sperm motility and fertilization have been reported. The expression of other relaxin related peptides, such as INSL5 and INSL6 was described in testis; yet, currently there are no experimental data to pinpoint their biological functions. The other member of relaxin peptide family, insulin-like 3 peptide (INSL3), is a major player in male development. The INSL3 peptide is expressed in testicular fetal and adult Leydig cells and is directly responsible for the process of abdominal testicular descent (migration of the testes towards the scrotum during male development). Genetic targeting of the Insl3 gene or INSL3 GPCR receptor Lgr8/Rxfp2 causes high intra-abdominal cryptorchidism due to a differentiation failure of testicular ligaments, the gubernacula. Several mutations of these two genes rendering nonfunctional proteins have been described in human patients with testicular maldescent. Thus, in this chapter we review the data related to the expression and function of relaxin and related peptides in male reproduction.

Sfrp1 and Sfrp2 are required for normal male sexual development in mice

Secreted frizzled-related proteins (Sfrps) are antagonists of WNT signalling implicated in a variety of biological processes. However, there are no reports of a direct role for Sfrps in embryonic organogenesis in mammals. Using in vivo loss-of-function studies we report here for the first time a redundant role for Sfrp1 and Sfrp2 in embryonic sexual development of the mouse. At 16.5 dpc, male embryos lacking both genes exhibit multiple defects in gonad morphology, reproductive tract maturation and gonad positioning. Abnormal positioning of the testis appears to be due to failed gubernaculum development and an unusually close association between the cranial end of the reproductive tract and the kidney. The testes of double homozygotes are smaller than controls, contain fewer cords from the earliest stages, but still express Insl3, which encodes the hormone required for gubernacular masculinisation. Lgr8, which encodes the Insl3 receptor, is also expressed in the mutant gubernaculum, suggesting that Sfrp1/Sfrp2 signalling is not required for expression of the ligand or receptor that controls transabdominal testicular descent. Similarities between the abnormalities of embryonic sexual development in Sfrp1(-/-)Sfrp2(-/-) embryos with those exhibited by the Looptail and Wnt5a mutants suggest that disrupted non-canonical Wnt signalling may cause these defects.

Relaxin signalling in primary cultures of human myometrial cells

In myometrium of pigs and rats, though not humans, relaxin appears to mediate an inhibition of spontaneous and oxytocin-induced contractility, presumably acting through a G-protein coupled receptor (RXFP1) to generate cAMP. In humans, circulating relaxin is highest in the first trimester, including the time of implantation, when transitory uterine quiescence could help a blastocyst to implant. We investigated whether relaxin can activate adenylate cyclase in primary human myometrial cells from non-pregnant tissue, and we show that relaxin is able to stimulate the generation of cAMP in a manner, which is dependent upon a tyrosine phosphorylation activity, as in the endometrium. We identified transcripts for the relaxin receptor RXFP1 as full-length variants, though a minor splice variant missing exon 2 was also present in low amounts. These cells also express transcripts encoding RXFP2, the receptor for the closely related hormone, INSL3. Although able to respond to relaxin at high concentrations, this receptor does not appear to function by contributing to the cAMP production in human myometrial cells, nor does INSL3 act as a functional agonist or antagonist of relaxin action. In conclusion, the inability of relaxin to inhibit contractility in human myometrial cells would appear to be due to events downstream of simple cAMP generation.

Mutations in the insulin-like factor 3 receptor are associated with osteoporosis

INTRODUCTION

Insulin-like factor 3 (INSL3) is produced primarily by testicular Leydig cells. It acts by binding to its specific G protein-coupled receptor RXFP2 (relaxin family peptide 2) and is involved in testicular descent during fetal development. The physiological role of INSL3 in adults is not known, although substantial INSL3 circulating levels are present. The aim of this study was to verify whether reduced INSL3 activity could cause or contribute to some signs of hypogonadism, such as reduced BMD, currently attributed to testosterone deficiency.

MATERIALS AND METHODS

Extensive clinical, biochemical, and hormonal study, including bone densitometry by DXA, was performed on 25 young men (age, 27-41 yr) with the well-characterized T222P mutation in the RXFP2 gene. Expression analysis of INSL3 and RXFP2 on human bone biopsy and human and mouse osteoblast cell cultures was performed by RT-PCR, quantitative RT-PCR, and immunohistochemistry. Real-time cAMP imaging analysis and proliferation assay under the stimulus of INSL3 was performed on these cells. Lumbar spine and femoral bone of Rxfp2-deficient mice were studied by static and dynamic histomorphometry and muCT, respectively.

RESULTS

Sixteen of 25 (64%) young men with RXFP2 mutations had significantly reduced BMD. No other apparent cause of osteoporosis was evident in these subjects, whose testosterone levels and gonadal function were normal. Expression analyses showed the presence of RXFP2 in human and mouse osteoblasts. Stimulation of these cells with INSL3 produced a dose- and time-dependent increase in cAMP and cell proliferation, confirming the functionality of the RXFP2/INSL3 receptor-ligand complex. Consistent with the human phenotype, bone histomorphometric and muCT analyses of Rxfp2(-/-) mice showed decreased bone mass, mineralizing surface, bone formation, and osteoclast surface compared with wildtype littermates.

CONCLUSIONS

This study suggests for the first time a role for INSL3/RXFP2 signaling in bone metabolism and links RXFP2 gene mutations with human osteoporosis.

Developmental Expression and Gene Regulation of Insulin-like 3 Receptor RXFP2 in Mouse Male Reproductive Organs1

The mutations of testicular insulin-like 3 (INSL3) hormone or its receptor RXFP2 cause cryptorchidism in male mice. Here we have examined Rxfp2 gene expression at different stages of embryonic and postnatal mouse development in male reproductive tissues employing quantitative RT-PCR and several RXFP2-specific antibodies directed toward different parts of the RXFP2 protein. Receptor expression was markedly increased after birth and was readily detectable in the epididymis, Leydig cells, and germ cells of the testis. The strongest expression was detected in adult mouse cremaster muscle. INSL3 treatment increased cell proliferation of embryonic gubernacular and TM3 embryonic Leydig cells, implicating active INSL3-mediated autocrine signaling in these cells and identifying TM3 as a novel in vitro model to study the effects of RXFP2 signaling. We generated Tg(Rxfp2-cre)Aia (Rxfp2-iCre) transgenic mice expressing improved Cre recombinase (iCre) under the control of the 2.4-kb mouse Rxfp2 promoter. The iCre was expressed in the gubernacular ligament at E14.5, indicating that this promoter is able to drive Rxfp2 gene expression during transabdominal testis descent. We demonstrated that the transcription factor Sox9, a known male sex determination factor, is expressed in mouse embryonic gubernacula and upregulated human, but not mouse, promoter luciferase reporter constructs. In conclusion, we have determined the developmental expression profile of INSL3 receptor employing newly characterized RXFP2 antisera and a novel Rxfp2-iCre transgenic mouse model. We determined the promoter region capable of providing the gubernacular-specific expression of Rxfp2. Analysis of RXFP2 promoter identified SOX9 as a new transcriptional enhancer of human gene expression.

Insulin-like factor 3 levels in cord blood and serum from children: effects of age, postnatal hypothalamic-pituitary-gonadal axis activation, and cryptorchidism

CONTEXT

The Leydig cell hormone insulin-like factor 3 (INSL3) is important for testicular descent. Currently INSL3 levels in cord blood, in serum throughout childhood, and in relation to congenital cryptorchidism are unknown.

OBJECTIVE

The objective of the study was to characterize INSL3 levels in cord blood during the postnatal activation of the hypothalamic-pituitary-gonadal axis and in later childhood in normal boys and girls and cryptorchid boys.

DESIGN AND PARTICIPANTS

Serum from 267 3-month-old boys of a prospective study with standardized cryptorchidism classification was analyzed for INSL3 (of these, 99 also had cord blood samples). Testicular position was known in 151 controls and 54 transiently cryptorchid and 62 persistently cryptorchid subjects. Eight infant girls, 26 boys (4.1-10.1 yr), and 13 girls (3.7-8.7 yr) were also included.

OUTCOME MEASURE

INSL3, age, testicular position, LH, and testosterone were measured.

RESULTS

INSL3 levels were significantly higher (P < 0.001) in cord blood and 3-month-old boys as compared with older prepubertal boys. At 3 months of age, INSL3 correlated significantly with LH in healthy boys. Cord blood INSL3 was significantly reduced in persistently cryptorchid boys (P = 0.001), and 3-month-old persistently cryptorchid boys had a significantly increased LH to INSL3 ratio (P = 0.014). INSL3 was unmeasurable in girls at all ages.

CONCLUSIONS

In boys, early postnatal INSL3 is markedly higher as compared with later childhood, presumably because it is stimulated by the transient postnatal LH peak. INSL3 was unmeasurable in girls at all ages. Reduced cord blood INSL3 and an increased LH to INSL3 ratio at 3 months of age in persistently cryptorchid boys suggest impaired Leydig cell function in cryptorchid boys already in the perinatal period.

Relaxin family peptide receptors Rxfp1 and Rxfp2: mapping of the mRNA and protein distribution in the reproductive tract of the male rat

BACKGROUND

Relaxin is the endogenous ligand of the G-protein coupled receptor RXFP1, previously known as LGR7. In humans relaxin can also activate, but with lower affinity, the closely related receptor for the insulin-like peptide from Leydig cells, RXFP2, previously known as LGR8. The lack of relaxin impairs male fertility but the precise distribution and the function of relaxin receptors in the male reproductive tract is not known. We investigated the distribution of Rxfp1 and Rxfp2 in the reproductive tract of the male rat and the function of relaxin in the vas deferens, a tissue with high expression of both receptors.

METHODS

The presence of mRNA for Rxfp1 and Rxfp2 was investigated in testes, cultured Sertoli cells, epididymis, vas deferens, seminal vesicle, prostate, and spermatozoa by RT-PCR and Southern blot. Protein expression in the testis, vas deferens, primary culture of Sertoli cells, and spermatozoa was assessed by immunohistochemistry and immunofluorescence. The role of relaxin in the vas deferens was evaluated by contractility studies and radioimmunoassay of cAMP production. The effect of relaxin on mRNA levels for metalloproteinase-7 was measured by Northern blot.

RESULTS

Transcripts for Rxfp1 and Rxfp2 were present in almost all parts of the male reproductive tract, with high levels in testis and vas deferens. Both receptors were immunolocalized in late stage germ cells but not in mature spermatozoa, although mRNAs for both receptors were also present in mature spermatozoa. Rxfp1 but not Rxfp2 was detected in cultured Sertoli cells. Strong immunostaining for Rxfp1 and Rxfp2 was seen in muscular and epithelial layers of the vas deferens and in arteriolar walls. Relaxin did not affect contractility and cyclic AMP production of the vas deferens, but increased the levels of mRNA for metalloproteinase-7.

CONCLUSION

Rxfp1 and Rxfp2 are widely and similarly distributed throughout the male reproductive tract. Our results suggest that Rxfp1 on spermatids and Sertoli cells may be important in spermatogenesis. Relaxin in the vas deferens does not affect contractility, but may affect vascular compliance and collagen and matrix remodeling.

Design, synthesis and pharmacological evaluation of cyclic mimetics of the insulin-like peptide 3 (INSL3) B-chain

Insulin-like peptide 3 (INSL3) is a peptide hormone belonging to the relaxin-insulin superfamily of peptides that plays important roles in testes descent, oocyte maturation and the control of male germ cell apoptosis. These actions are mediated via a specific G-protein coupled receptor, LGR8. Previous structure-activity studies have shown that the key binding site of INSL3 is situated within its B-chain. Recent studies in our laboratory have led to the identification of a cyclic peptide mimetic 2 of the INSL3 B-chain, which we have shown to compete with the binding of [33P]-relaxin to LGR8 expressed in HEK293T cells, and to inhibit cAMP-mediated signaling in these cells, i.e. it is an antagonist of INSL3. In order to further define the structure-activity relationships of cyclic analogues of the INSL3 B-chain, we used a structure-based approach to design a series of cyclic, disulfide-constrained INSL3 B-chain mimetics. To do this, we first created a model of the 3D structure of INSL3 using the crystal structure of human relaxin as a template. This model of INSL3 was then used as a template to design a series of disulfide-constrained mimetics of the INSL3 B-chain. The peptides were synthesized by solid-phase peptide synthesis using pseudoproline dipeptides to improve the synthesis outcome. Of the seven prepared INSL3 B-chain mimetics, three compounds were found to have partial displacement activity, while four were able to completely displace [33P]-relaxin from LGR8, including compounds that were markedly shorter than compound 2. The best of these, mimetic 6, showed significantly greater affinity for LGR8 than compound 2, but still displayed around 1000-fold less affinity for LGR8 than native INSL3. Analysis of selected mimetics for their alpha-helical content using circular dichroism (CD) spectroscopy revealed that, generally, the mimetics showed less than expected helicity. The inability of the compounds to display true native INSL3 structure is likely contributing to their reduced receptor binding affinity. We are currently examining alternative INSL3 B-chain mimetics that might better present key receptor binding residues in the native INSL3-like conformation.

T222P mutation of the insulin-like 3 hormone receptor LGR8 is associated with testicular maldescent and hinders receptor expression on the cell surface membrane

Insulin-like 3 (INSL3) hormone plays a crucial role in testicular descent during embryonic development. Genetic ablation of Insl3 or its G protein-coupled receptor (GPCR) Lgr8 causes cryptorchidism in mice. Previously, we identified a nonfunctional T222P mutation of LGR8 in several human patients with testicular maldescent. Using a large population of patients and healthy controls from Italy, we have demonstrated that T222P LGR8 mutation is present only in affected patients (19 T222P/+ of 598 vs. 0/450, P < 0.0001). We have also identified a novel allele of LGR8 (R223K) found in one patient with retractile testes. Both mutations are located in the leucine-rich repeats (LRRs) of GPCR ectodomain. The expression analysis of T222P mutant receptor transfected into 293T cells revealed that the mutation severely compromised GPCR cell membrane expression. The substitution of Thr(222) with the neutral Ser or Ala, or the R223K mutation, did not alter receptor cell membrane expression or ligand-induced cAMP increase. Additional mutations, affecting first leucine in a signature LxxLxLxxN/CxL stretch of LRR (L283F), or the amino acid residues, forming the disulfide bond or coordinating calcium ion in the LDLa module (C71Y and D70Y), also rendered proteins with reduced cell surface expression. The structural alterations of both LRRs and LDLa of the ligand-binding part of LGR8 cause the inability of receptor to express on the cell surface membrane and might be responsible for the abnormal testicular phenotype in patients.

Changes in serum insulin-like factor 3 during normal male puberty

CONTEXT

Insulin-like factor 3 (INSL3) is produced by the Leydig cells, and in adults, its secretion is dependent on the state of differentiation of these cells, which, in turn, is dependent on LH. However, the secretion and regulation of INSL3 during puberty is unknown.

OBJECTIVE

Our objective was to evaluate INSL3 concentrations during normal male puberty and the relation of INSL3 to LH, FSH, and testosterone.

DESIGN AND SETTING

We conducted a cross-sectional study from January to December 2005 at academic clinics.

PATIENTS

Participating in the study were 75 healthy male subjects aged 9.5-17.5 yr, homogeneously distributed into five pubertal groups of 15 according to Tanner stages.

MAIN OUTCOME MEASURES

We assessed mean testicular volume and LH, FSH, testosterone, and INSL3 concentrations in relation to age and pubertal stage.

RESULTS

We observed an increase of INSL3 and LH levels from Tanner stage 2 to 4, and an increase of FSH from stage 2 to 3. Testosterone levels increased from stage 3 to 4. No differences were seen for all measured hormones between stages 4 and 5. The increase in INSL3 seemed therefore to anticipate the increase in testosterone. However, INSL3 plasma concentrations at pubertal stages 4 and 5 are about one fourth of adult levels, whereas FSH, LH, and testosterone reached adult levels by stage 4. Positive significant correlations were found between INSL3 and LH for all pubertal stages.

CONCLUSIONS

This study provides information on the physiological dynamics of INSL3, showing that the serum concentrations of this hormone increased progressively throughout puberty under the differentiating action of LH on Leydig cells. INSL3 is therefore confirmed to represent a marker of Leydig cell differentiation and function. However, a prolonged exposure to LH seems to be necessary to reach INSL3 concentrations of adults. A possible use of INSL3 in puberty disorders is promising.