Andrology and Infertility Research
Our translational research program combines investigation into the basic science rationale (i.e. genetics, molecular biology) behind disease processes with an understanding of the clinical issues faced by patients and providers.
Although it has been known for more than a century that boys with undescended testes (UDT) are at risk for low sperm counts and infertility, the reason for this has never been fully understood. The average age at which young boys undergo surgery to correct this problem is about 6 to 12 months, yet the age when one may reliably assess semen quality is 18 years.
We have undertaken a major research effort to follow boys from birth through 18 years to learn more about the long-term problems of infertility and testicular cancer. Over the past two decades, we have enrolled 140 patients who have agreed to periodic semen analysis as well as genetic testing (described below).
Using modern molecular techniques, scientists are able to amplify key segments of human DNA and determine their sequence. We are currently searching for single base-pair alterations that correlate with infertility in the population of patients with consistently low sperm counts.
Another novel approach to the study of infertility in these patients involves the use of microarray methods to search for changes in gene expression within the sperm of patients with cryptorchidism. Using this approach, it has been possible to identify decreases in the expression of the tpx-1 gene that correlate highly with low sperm counts. These surprising findings would not have come to light without the power of modern microarray methods, which allow for the simultaneous detection of shifts in the expression of more than 20,000 genes at one time.
Three areas of cryptorchidism research are currently active, each of which overlap with the others:
- A follow-up clinical database of patients with a history of surgically corrected cryptorchidism. Current evaluation is correlating anatomic information and bilateral testis histology with follow-up semen analysis, testis ultrasound and hormonal data.
- Molecular research aimed at the genes associated with the etiology of cryptorchidism and the long-term possibility of infertility. Several rodent models have identified UDT in knockout models of HOXA10, HOXA11, HOX13, CGRP, INSL3 and great genes. Homeobox genes play a key role in the morphogenesis of segmental body structures along the primary anterior-posterior body axis including the genitourinary system. Human genomic analysis of HOXA9 did not reveal mutations unique to UDT patients. A previously unreported highly-polymorphic region in exon2 was identified in both control and UDT patients. Sequence alterations of HOXA10 were found in 30/45 UDT patients and single nucleotide polymorphisms (SNP) are present in both the control and UDT populations. The HOXD13 homozygous variant A60A is more common in bilateral UDT and an abnormal adult sperm concentration. Thirty-nine UDT patients underwent simultaneous CGRP, INSL3, and HOXD13 analysis; 22 patients with recessive alleles in SNPs of any of the three genes were identified; 21 percent of the UDT patients have two genes with recessive alleles.
- Molecular research (microarray of RNA) from the sperm of cryptorchid men to identify novel genes associated with poor seminal parameters. Microarray results on 10 control patients (mean age 28.5 years) and 12 cryptorchid males (mean age 18.3 years; 8 unilateral, 4 bilateral). Motile sperm were isolated by Percoll centrifugation, the total RNA extracted and verified using sperm-specific RT-PCR. Biotin-labeled amplified RNA was hybridized to Affymetrix Human Genome Focus Arrays. Mean sperm density was significantly decreased between control, unilateral and bilateral cryptorchid samples (110 vs. 80 vs. 16 million/cc, p=0.05). From the microarray expression data, we identified 43 genes differentially expressed between the two groups. Of these, 38 genes were significantly under-expressed in the cryptorchid samples including many transcriptional factors (cul3, prm1, hspcd35). Among the 38 was a testis-specific cell-adhesion gene (tpx-1) involved in germ cell maturation and sperm tail formation. An apoptotic gene (TNF-alpha induced protein 3) was highly over-expressed (p=0.001) in the cryptorchid samples suggesting a role for apoptosis as a cause for poor sperm densities.
Gene expression profiles offer unprecedented insight into the diverse alterations that occur in cryptorchidism. The observed changes in spermatozoal expression of transcriptional and apoptotic genes may result in poor seminal parameters found in boys with a history of cryptorchidism.
Some recent publications from this work include:
- Patel RP, Kolon TF, Huff DS, Carr MC, Zderic SA, Canning DA, and Snyder HM 3rd. Testicular microlithiasis and antisperm antibodies following testicular biopsy in boys with cryptorchidism. J Urol. 2005 Nov;174(5):2008-10; discussion 2010. Read the abstract»
- Patel RP, Kolon TF, Huff DS, Carr MC, Zderic SA, Canning DA, Snyder HM 3rd. Cryptorchid testis histopathology in myelomeningocele patients. J Pediatr Urol. 2008 Dec;4(6):434-7. Epub 2008 Jul 21. Read the abstract»
- Nguyen MT, Delaney DP, and Kolon TF. Gene expression alterations in cryptorchid males using spermatozoal microarray analysis. Fertil Steril. 2009 Jul;92(1):182-7. Epub 2008 Aug 8. Read the abstract»
Varicocele is an abnormal enlargement of the veins in the scrotum draining the testicles. A urology patient database at The Children's Hospital of Philadelphia tracks the varicocele size, symptoms and testicular volumes over time with follow-up semen analyses as young adults.
Our research has found:
- The pubertal and adolescent testes may undergo asynchronous growth spurts. Sustained significant poor growth of the left testis associated with a varicocele is less common than was previously expected. In those cases of sustained poor growth, a microscopic subinguinal varicocele repair yields excellent (>95 percent) success rates. (see Kolon TF, Clement MR, Cartwright L, et al. Transient asynchronous testicular growth in adolescent males with a varicocele. J Urol. 2008 Sep;180(3):1111-4; discussion 1114-5. Epub 2008 Jul 18).
- Patients with a varicocele are significantly taller than age-matched controls. Although our examination of the body mass index did not show any significant difference compared to controls. Subsequent studies have corroborated our height findings in addition to the theory that increased BMI is protective of varicocele presence. (See Delaney DP, Carr MC, Kolon TF, Snyder HM 3rd, Zderic SA. The physical characteristics of young males with varicocele. BJU Int. 2004 Sep;94(4):624-6).
- We also correlated differential and total testicular volumes with semen analyses obtained once patients had reached 18 years of age. The mean sum of the total testicular volumes (right and left) taken at the last ultrasound differed substantially for those patients with a total sperm count less than 40 million (35.1 ± 10.9 cc) versus those with a count above 40 million (43.5 ± 9.9 cc) (p= 0.02). From these data we concluded that:
- Differential testicular volumes change during adolescence in a population of boys followed by observation.
- Differential testicular volume is not predictive of future total sperm count.
- The diminished bilateral testicular volume observed in those patients with the worst semen parameters supports a possible underlying endocrinopathy.
Germ cell preservation
The Urology Division is part of a multispecialty collaboration between clinicians and basic scientists to achieve a goal of identifying and expanding spermatogonial stem cells (SSCs) from testicular tissue in at-risk patients. We offer testicular cryopreservation to prepubertal boys who are at risk for infertility from cancer therapy and explore the laboratory science required for both in vitro expansion of SSC and methods for freezing testicular tissue for future use.
- Pure populations of prepubertal human spermatogonia and mouse gonocytes were generated from testis biopsies. Stem cell potential of human germ cells was demonstrated by transplantation to mouse testes, following which the cells migrated to the basement membrane of the seminiferous tubule and were maintained similar to SSCs.
- Expression of genes previously identified as SSC and spermatogonial-specific markers (e.g., zinc-finger and BTB-domain containing 16, ZBTB16) was greatly elevated in both human spermatogonia and mouse gonocytes compared to somatic cells. Several novel genes were expressed at significantly higher levels in germ cells of both species. Genes known to be essential for mouse SSC self-renewal were more highly expressed in both prepubertal human spermatogonia and mouse gonocytes than in somatic cells. Human cells transplanted to recipient mouse seminiferous tubules previously treated with cadmium were found in small groups in colonies and with greater percentage than somatic cells.