Cryptorchidism disrupts the earliest transitions of male germ cells and compromises long-term fertility potential. Here I summarize our basic and clinical investigations into (i) germ-celland Sertoli-cell changes in experimental and human cryptorchidism, (ii) molecular candidates involved in the differentiation process from gonocytes to spermatogonia, (iii) the timing benefit of early orchiopexy, and (iv) endocrine modifiers, including androgen signaling and neonatal thyroid status. Across rat models and pediatric cohorts, we observe delayed gonocyte resettlement to the basement membrane, reduced undifferentiated type-A spermatogonia, Sertoli-cell junctional disorganization (Claudin-11/blood-testis barrier (BTB), and transcriptional shifts implicating histone demethylation (KDM5A), FOXO1 regulation by miR-135a, and tight junction remodeling. In bilateral cryptorchidism, lower inhibin-B–to-FSH ratios track with depressed germ-cell counts at biopsy; combining AMH, inhibin B, and FSH yields strong ROC performance for predicting poor germ-cell indices, supporting pre-operative endocrine triage.
La cryptorchidie perturbe les premières transitions des cellules germinales mâles et compromet le potentiel de fertilité à long terme. Cette synthèse présente nos travaux fondamentaux et cliniques portant sur : (i) les altérations des cellules germinales et de Sertoli dans la cryptorchidie expérimentale et humaine ; (ii) les candidats moléculaires impliqués dans la différenciation gonocyte → spermatogonie ; (iii) le bénéfice temporel d’une orchidopexie précoce ; et (iv) les modulateurs endocriniens, incluant la signalisation androgénique et le statut thyroïdien néonatal.
Dans les modèles murins et les cohortes pédiatriques, nous observons un retard du repositionnement des gonocytes vers la membrane basale, une diminution des spermatogonies A indifférenciées, une désorganisation jonctionnelle des cellules de Sertoli (Claudin-11/barrière hématotesticulaire), et des remaniements transcriptionnels impliquant la déméthylation histonique (KDM5A), la régulation de FOXO1 par miR-135a et le remodelage des jonctions serrées. En cryptorchidie bilatérale, le ratio inhibine B/FSH reflète la pauvreté germinale à la biopsie, et l’association AMH–inhibine B–FSH améliore la prédiction des faibles indices germinaux.
Cryptorchidism is among the most common congenital anomalies in boys and is a leading risk factor for subfertility and testicular cancer later in life. Neonatal, transient hypothyroidism increases undifferentiated spermatogonia in rats and associates with higher
germ-cell counts in boys with a history of congenital hypothyroidism, suggesting a modulatory role for thyroid hormone in early spermatogonial differentiation. Collectively, these data argue that cryptorchidism perturbs germ-cell fate decisions and Sertoli barrier maturation during a narrow postnatal window—defects that are partly mitigated by timely orchiopexy and potentially readable by minimally invasive hormone panels. [1–3] The two-phase model of testicular descent—an insulin-like 3 (INSL3)-dominated transabdominal phase and an androgen-dependent inguinoscrotal phase—provides a useful framework for mechanistic thinking, and both phases can be perturbed by environmental anti-androgens in experimental systems [2–4]. Beyond mechanical malposition and thermal stress, our work focuses on germ-cell biology during the first postnatal months (“mini-puberty”) and prepuberty, when gonocytes should migrate to the basement membrane, reprogram into undifferentiated spermatogonia (including UTF1+ and GFRA1+ subsets), and establish the spermatogonial stem-cell (SSC) pool that seeds lifelong spermatogenesis [1–3,5]. We summarize evidence from our laboratory and university hospital in Nagoya, integrating transcriptomic screens, animal models, and pediatric biopsy-linked endocrine phenotypes.
In flutamide-exposed rats, we performed orchiopexy at 4–7 weeks and assessed testis architecture at 10 weeks, comparing with non-operated cryptorchid controls [1].
We applied IHC for UTF1 (gonocyte/undifferentiated spermatogonia marker), DDx4/MVH (germ-cell cytoplasmic marker), and GFRA1 (undifferentiated type-A spermatogonia/SSC compartment) with time-course quantification at postnatal day (PND) 9 and beyond [1,5,12]. Microarray profiling at PND9 contrasted descended vs undescended testes; separate microRNA arrays surveyed regulatory small RNAs [1,13,14].
Claudin-11 distribution (BTB component) was evaluated by confocal microscopy and ultrastructure by electron microscopy; junctional integrity was scored per tubule cross-section [1,6,15].
In a single-center pediatric series of orchiopexy (N=323; biopsies analyzed in N=146), we quantified germ-cell number per tubule cross-section (G/T; DDx4 based), testicular volume, and recorded laterality/position. Pre-operative serum inhibin B, AMH, LH, FSH were analyzed; ratios (e.g., inhibin B:FSH) and receiver–operating characteristic (ROC) analyses were used to predict low G/T [1,16].
To model neonatal hypothyroidism, dams received propylthiouracil in drinking water for 7 days postpartum; male offspring testes were examined for GFRA1+ and DDx4+ cells. In our human series, we compared germ-cell indices in cryptorchid boys with vs without a history of congenital hypothyroidism [1,17].
When orchiopexy was performed at 4–7 weeks in the rat model, testes harvested at 10 weeks displayed improved tubule caliber and reduced histological damage compared with uncorrected cryptorchid testes; the benefit diminished as age at correction increased, underscoring a narrow therapeutic window [1,18].
When orchiopexy was performed at 4–7 weeks in the rat model, testes harvested at 10 weeks displayed improved tubule caliber and reduced histological damage compared with uncorrected cryptorchid testes; the benefit diminished as age at correction increased, underscoring a narrow therapeutic window [1,18].
At PND9, undescended testes contained more centrally located gonocytes and fewer peripherally positioned type-A spermatogonia than controls, consistent with delayed migration/resettlement to the basement membrane (UTF1+ quantification) [1,5,12]. This spatial lag implies SSC pool under-establishment, a likely substrate for later quantitative germ-cell loss.
Microarray at PND9 identified upregulation of Kdm5a (H3K4 demethylase) in undescended testes; IHC localized KDM5A to germ cells [1]. Given KDM5A’s role in removing H3K4 methylation (an activation-associated mark), over-activity could blunt transcriptional programs needed for SSC differentiation, converging with independent evidence that histone modifications gate SSC fate [7,13]. MicroRNA analysis showed downregulation of miR-135a in undescended testes, and functional assays supported miR-135a targeting of FOXO1; nuclear FOXO1-positive SSCs were reduced in cryptorchid testes [1,8]. Since FOXO1 is pivotal for SSC maintenance and stress responses, impaired miR-135a–FOXO1 tuning offers a plausible axis for early germ-cell vulnerability [8,14].
Claudin-11 staining, normally forming continuous linear belts at puberty, appeared discontinuous/patchy in cryptorchid testes up to 4 weeks; the proportion of tubules with abnormal claudin-11 distribution was significantly higher than in controls. Ultrastructural analysis corroborated BTB disarray, and apoptosis was increased, consistent with the notion that premature BTB failure deprives developing germ cells of niche protection [1,6,15].
Subtractive cDNA analysis comparing biopsies from hydrocele vs cryptorchid boys identified 18 up-regulated and 16 down-regulated genes in cryptorchid testes; qPCR confirmed increased TPT1, EEF1A1, and NuMA1 gene, each expressed in germ cells across spermatogenesis [1,19]. Morphometry showed reduced G/T in bilateral vs unilateral cryptorchidism.
In the pediatric cohort, bilateral cryptorchidism showed significantly lower inhibin B:FSH ratios and lower G/T than unilateral cases. In bilateral cases <24 months, composite endocrine indices (inhibin B:FSH, AMH:FSH, and FSH) predicted low G/T with high accuracy (AUC >0.9), enabling cutoffs to triage boys at highest risk for germ-cell loss before surgery [1]. These observations mirror broader literature linking inhibin B (Sertoli output) and FSH (pituitary input) with Sertoli/germ-cell status in early life [3,16].
In the transient neonatal hypothyroid rat model,PND7 and PND20 males males had higher counts of DDx4+ germ cells and GFRA1+ undifferentiated spermatogonia than controls, implying that reduced neonatal thyroid hormone favors SSC-state retention or delayed differentiation [1,9]. In boys with cryptorchidism, a history of congenital hypothyroidism associated with higher germ-cell numbers at biopsy, paralleling the animal data [1]. These preliminary findings suggest that thyroid hormone participates in in the differentiation process from gonocytes to spermatogonia. [17]
In SRY-negative 46,XX testicular DSD, we identified upregulation of ROCK1 in XX testis biopsy material [20] and, in a series of four cases, recurrent copy-number gain upstream of SOX3 on chromosome X; given structural similarity between SOX3 and SRY, these data support an SRY-independent SOX3 pathway for human testis determination in a subset of cases [1,10]. SOX3 duplications have been reported by others in SRY-negative 46,XX testicular DSD [10,21].
In embryoid-body systems directing mouse pluripotent cells toward germ-cell–like lineages, higher glucose media increased MVH/DDx4-positive germ-cell-like cells; subtraction cloning identified Txnip, RuvBl2, Pttg, and and other candidates enriched under high glucose, with expression confirmed in fetal through adult germ cells [1]. Although mechanistic dissection remains pending, the data point to metabolic gating of germ-cell fate acquisition [22].
Our integrated datasets converge on a simple narrative: cryptorchidism perturbs two coupled developmental programs during a restricted postnatal window—(i) germ-cell lineage timing (basement-membrane resettlement and SSC establishment) and (ii) Sertoli-cell barrier maturation. Fetal anti-androgen exposure reproduces both positional failure and early testicular immaturity; early orchiopexy partially rescues the niche, strengthening the case for prompt surgery [1–4,11,12,15,18].
Germ-cell timing defects. The accumulation of centrally located gonocytes at PND9 in undescended testes implies a failure to complete the migration and differentiation sequence that should yield UTF1+/GFRA1+ SSCs at the periphery. Chromatin remodeling (KDM5A upregulation; decreased H3K4 methylation) and FOXO1 dysregulation via reduced miR-135a provide mechanistic footholds that could slow exit from a progenitor state or impair SSC maintenance [1,7,8]. These axes align with mounting evidence that histone and transcription-factor circuits set SSC competence and stress resilience [13,14].
Sertoli barrier and microenvironment. BTB formation is a hallmark of pubertal Sertoli maturation; disorganized claudin-11 belts and ultrastructural BTB defects in cryptorchid testes match reports that BTB integrity is crucial to germ-cell survival and progression [1,6]. A compromised BTB likely amplifies thermal and oxidative stress sensitivity and facilitates apoptosis, compounding primary germ-cell timing defects [15].
Clinical translation. Our endocrine–histology correlations suggest that low inhibin B:FSH (and related AMH indices) can flag bilateral cryptorchid boys at high risk of germ-cell depletion before orchiopexy. Such panels could prioritize earlier intervention and inform parental counseling. The strong ROC values in bilateral cases underscore the value of combining Sertoli-derived (inhibin B, AMH) and pituitary (FSH) readouts [1,16].
Endocrine modulators beyond androgens. The neonatal hypothyroidism data in rats and the signal in boys with congenital hypothyroidism are provocative: thyroid hormone appears to influence the tempo of SSC emergence vs maintenance. While the directionality (more GFRA1+ cells) could be protective or reflect delayed differentiation, either scenario has implications for the timing of repair and adjuvant therapies [1,9,17].
Limitations and next steps. Many results are single-center and require replication across populations. Microarray signals (KDM5A/miR-135a) need causal testing in vivo (gain-/loss-of-function in SSCs) and integration with single-cell multi-omics across cryptorchid and control testes. BTB alterations should be mapped against functional paracellular permeability assays. Endocrine cutoffs demand external validation and age-adjusted nomograms.
Early-stage spermatogenesis in cryptorchidism is derailed by delayed gonocyte migration/differentiation and immature Sertoli-cell barrier assembly, processes that are transcriptionally and epigenetically tunable and endocrinologically readable. Early orchiopexy improves architecture, and composite Sertoli/pituitary hormone panels can help identify boys at greatest risk of germ-cell loss. The interplay of androgen, thyroid, and chromatin-regulatory pathways defines an actionable window for preserving the SSC pool and lifelong fertility potential. [1–4,6–9]
I thank Prof. Yutaro Hayashi (past President, Japanese Society of Pediatric Urology) and Prof. Yoshiyuki Kojimafor mentorship; the Nagoya City University pediatric urology team for surgical and research support; and collaborating pathologists and laboratory staff for histology and molecular analyses. [1]
