published_or_final_version / abstract / toc / Physiology / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Adelaide, Dept. of Animal Science, 1997? / Includes bibliographical references (leaves 169-205).

Thesis (M.Sc. (Pharmacology)) -- Mahidol University, 1979.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 154-169). Also available via the Internet.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Also available online.

The mammalian testis is divided into two distinct compartments which carry out its principal functions. Spermatogenesis occurs within the seminiferous tubules and androgen biosynthesis primarily occurs in the interstitial space. Both these processes are entirely dependent upon the two major testicular somatic cell populations - the Sertoli and Leydig cells respectively. In human males, testicular spermatogenic and endocrine function declines during the ageing process. Of particular significance is the reported age-related decrease in Leydig cell androgen production as androgens have been suggested to play a crucial role in supporting lifelong general health in men, with low circulating testosterone linked to an increased risk of developing chronic age-related cardiometabolic diseases. However, the relationship between ageing, testicular function and disease is not fully understood, impeding the development of novel therapeutic strategies to treat age-related testicular dysfunction. In one set of studies undertaken herein, a series of novel mouse models of premature ageing were utilised to begin to dissect the process of age-related testicular degeneration. Firstly, a novel knockout-first conditional allele of a previously reported premature-ageing model driven by Cisd2 (CDGSH Iron Sulphur Domain 2) deficiency was validated and the testicular phenotype characterised and compared to that of naturally aged mice at 18-months of age. Histological analyses revealed premature testicular atrophy at 6-months of age in CISD2 deficient mice, consistent with observations of the naturally aged testis. Circulating testosterone was significantly lower in CISD2-deficient mice compared to wild-type controls at 6-months of age and the luteinising hormone/testosterone ratio was significantly elevated, indicative of compensated Leydig cell failure. mRNA expression of key genes involved in androgen production were also significantly reduced in the CISD2-deficient testis, pointing to Leydig cell dysfunction in this model of premature aging. Next, Cre/LoxP technology was used to delete Cisd2 from specific testicular cell populations to determine which cell types control/support Leydig cell function during the ageing process. Testosterone production was unaffected when Cisd2 was disrupted in either the Leydig cell population or Sertoli cell population. These observations suggest that disruption to the testicular microenvironment in which Leydig cells reside, rather than intrinsic Leydig cell ageing, may play a significant role in age-associated Leydig cell dysfunction. A second set of studies were carried out to investigate the role of leukemia inhibitory factor (LIF) signalling in the maintenance of testicular function. LIF is a pleiotropic cytokine belonging to the interleukin-6 family. In the rodent testis, LIF is expressed in fetal life and adulthood; the peritubular myoid cells thought to be the main site of production. Given their anatomical location within the testis, LIF produced by peritubular myoid cells may act on both intratubular and interstitial cells to influence spermatogenesis and steroidogenesis respectively. Indeed, LIFR is expressed in germ cells, Sertoli cells, Leydig cells as well as testicular macrophages suggesting that LIF may be a key paracrine regulator of testicular function. However, the precise role of LIF/LIFR signalling in the testis is largely unknown. As such, models of testicular cell-specific Lifr deletion were generated using Cre/LoxP technology. Analysis of these novel models of conditional LIFR ablation revealed that LIFR is dispensable in germ cells for normal spermatogenesis. However, LIFR ablation from Sertoli cells resulted in a progressive degenerative phenotype, characterised by abnormal germ cell loss, sperm stasis, seminiferous tubule distention and subsequent atrophy of the seminiferous tubules. In a final set of studies, a rat model of Leydig cell ablation-regeneration was used to determine the regenerative capacity of human adipose-derived perivascular stem cells (hAd-PSC) as a potential therapy for testicular dysfunction. Following ethane dimethanesulphonate (EDS) mediated Leydig cell ablation, primary hAd-PSCs, cultured with or without LH, IGF-1, PDGFBB, T3 and ITS supplement, were transplanted into the rat testis and Leydig cell regeneration was monitored via serial measurements of circulating luteinising hormone (LH) and testosterone. Overall, hAd- PSCs had no impact on the recovery of circulating testosterone levels. However, when pre-cultured with the cocktail of hormone/growth factor supplements, the LH spike induced by the removal of testosterone negative feedback was dampened, suggesting the transplanted cells may promote Leydig cell regeneration. Whether these cells differentiate into Leydig cells, or simply provide paracrine support to the regenerating Leydig cells remains to be determined. Although Ad-PSCs may enhance regeneration kinetics, the transplanted cells were undetectable in the testis 5 weeks post transplantation suggesting they may not survive in the context of long term xenogeneic transplantation.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

published_or_final_version / abstract / Anatomy / Master / Master of Philosophy

<p>Rezultati prikazani u ovom radu opisuju efekte in vivo primene atrazina (2-hloro-4-<br />etilamino-6-izopropilamino-s-triazin) na ex vivo steroidogenezu u Leydig-ovim ćelijama<br />peripubertalnih pacova (tretiranih sa 50 mg/kg i 200 mg/kg telesne mase od 23. do 50.<br />dana starosti). Dobijeni rezultati jasno ukazuju da 28-dnevna in vivo primena atrazina<br />snažno inhibira testikularnu steroidogenezu, smanjujući ekspresiju gena za steroidogene<br />enzime i druge regulatorne proteine uključene u kontrolu testikularne steroidogeneze u<br />Leydig-ovim ćelijama peripubertalnih pacova. Rezultati in vivo primene atrazina<br />pokazuju da atrazin snažno inhibira ekspresiju gena za luteinizirajući hormon receptor<br />(LHR), skevendžer receptor-B1 (SR-B1), steroidogeni faktor-1 (SF-1), steroidogeni<br />akutni regulatorni protein (StAR), translokator protein (TSPO), fosfodiesterazu 4B,<br />3&beta;&minus;hidroksisteroid dehidrogenazu (&Eta;SD), CYP17A1 i 17&beta;HSD. Rezultati u okviru ovih<br />istraživanja pokazuju da primena atrazina tokom prepubertalnog perioda razvoja mužjaka<br />pacova dovodi do dozno-zavisnog smanjenja nivoa cAMP i snažne inhibicije androgeneze<br />u prisustvu hCG. Obzirom na blokadu ekspresije LHR, prvog elementa u aktivaciji<br />cAMP-signalnog puta, moglo bi se predpostaviti da je to uzrok blokade androgeneze kod<br />atrazinom-tretiranih životinja. Takođe, rezultati ukazuju na inhibiciju supstrat-stimulisane<br />produkcije androgena paralelno sa redukcijom ekspresije steroidogenih enzima CYP17A1<br />i 17&beta;HSD. U drugom delu ove doktorske disertacije, ispitivan je efekat direktne in vitro<br />primene različitih doza atrazina (1 nM, 1 &mu;M, 20 &mu;M, 50 &mu;M) na ekspresiju i aktivnost<br />steroidogenih enzima u kulturi preči&scaron;ćenih Leydig-ovih ćelija testisa peripubertalnih<br />pacova, pri čemu je zabeleženo stimulatorno dejstvo pomenutog herbicida. Naime,<br />zabeleženo je povećanje bazalne i hCG-stimulisane produkcije testosterona praćeno<br />povećanim nivoom cAMP u medijumu tretiranih ćelija. Pri ispitivanju ekspresije gena za<br />steroidogene enzime i regulatorne proteine, zabeleženo je povećanje ekspresije gena za<br />SF-1, StAR, CYP17A1 i 17&beta;HSD u hCG-stimulisanim uslovima. Takođe, povećana je i<br />produkcija testosterona nakon dodavanja progesterona i androstendiona kao supstrata,<br />kod Leydig-ovih ćelija tretiranih sa atrazinom. Da bi poku&scaron;ali da objasnimo za&scaron;to postoje<br />razlike u efektu atrazina u zavisnosti od načina primene, postavili smo jednokratni in vivo<br />eksperiment sa atrazinom (tretman sa 50 mg/kg i 200 mg/kg telesne mase, životinje<br />tretirane 50. dana starosti). Rezultati ovih eksperimenata ukazali su na up-regulaciju<br />testikularne steroidogeneze, kao i na povećan nivo cAMP kod životinja tretiranih sa<br />atrazinom Stoga, nivo cAMP se pojavljuje kao karika koja povezuje sva tri kori&scaron;ćena<br />eksperimentalna pristupa. Međutim, ostaje otvoreno pitanje na koji način atrazin utiče na<br />modulaciju nivoa cAMP i to pitanje predstavlja motiv za dalja istraživanja. Sumarno,<br />dobijeni rezultati ukazuju da 24-časovni tretman atrazinom izaziva povećanje, a<br />prolongirani tretman snažno smanjenje steroidogenog kapaciteta Leydig-ovih ćelija<br />peripubertalnih pacova.</p> / <p> In the present study, we investigated the effects of oral dosing of atrazine (2-chloro-4-<br /> ethylamino-6-isopropylamino-s-triazine) to peripubertal male rats (50 mg/kg and 200<br /> mg/kg body weight daily from postnatal day 23 to 50) on ex vivo Leydig cell<br /> steroidogenesis. Leydig cells from treated rats were characterised by significant decline in<br /> mRNA transcripts of several genes responsible for steroidogenesis: luteinizing hormone<br /> receptor (LHR), scavenger receptor-B1, steroidogenic acute regulatory protein (StAR),<br /> translocator protein, steroidogenic factor-1 (SF-1), phosphodiesterase 4B,<br /> 3&beta;&minus;hydroxysteroid dehydrogenase (&Eta;SD), CYP17A1 and 17&beta;HSD. In the presence of<br /> human chorion gonadotropin, the dose-dependent decrease in extra cellular cAMP level<br /> and accordingly strong inhibition of androgenesis were obtained. The transcription of<br /> LHR gene in Leydig cells of atrazine-treated rats was down-regulated in a dose-dependent<br /> manner, which could be the reason for reduction in cAMP level and expression of cAMPdependent<br /> genes. The results also indicated inhibition of substrate-stimulated androgen<br /> production in parallel with reduced expression of steroidogenih enzymes CYP17A1 and<br /> 17&beta;HSD. In the second part of this study we examined direct 24 h in vitro effect of<br /> different doses of atrazine (1 nM, 1 &mu;M, 20 &mu;M, 50 &mu;M) on expression and activity of<br /> steroidogenic enzymes in purified Leydig cells obtained from peripubertal rats. Obtained<br /> results indicated that 24 h-incubation of peripubertal Leydig cells in the presence of<br /> atrazine increased steroidogenic capacity of that cells. Increased basal and hCGstimulated<br /> testosterone production were accompanied by increasing levels of cAMP in the<br /> medium of treated cells. Also, in comparison to controls, gene expression revealed<br /> increased expression of SF-1, StAR, CYP17A1 and 17&beta;-HSD. When Leydig cells were<br /> challenged with progesterone and &Delta;4&ndash;androstenedione, testosterone production was<br /> increased in atrazine chalenged Leydig cells. To address these two opposite effects of<br /> atrazine we performed 24 h in vivo experiment in which peripubertal male rats (on<br /> postnatal day 50) were exposed to single atrazine treatment (50 mg/kg- and 200 mg/kgbody<br /> weight by gavage), and 24 h later, Leydig cells were isolated and testosterone levels<br /> in medium determined in basal and in hCG-stimulated conditions after 2 h-incubation<br /> period. Obtained results indicated that single in vivo exposure to atrazine was also<br /> accompanied 24 h later by up-regulation of Leydig cell androgenesis and increased cAMP<br /> level. According to the results obtained in this study, it seems that modulation of cAMP<br /> levels appear as a link that connects all three experimental approaches. However, the<br /> question of how atrazine affects the modulation of cAMP levels remains open, and<br /> present a motive for further research. In concluson, obtained results indicated that 24 h<br /> treatment with atrazine caused an increase, while prolonged treatment strongly reduce<br /> steroidogenic capacity of peripubertal Leydig cells.</p>

Includes bibliographical references (leaves 169-205). / xvii, 205, [33] leaves, [10] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Suggests that the testicular macrophage exhibits characteristics similar to that of a suppressor macrophage phenotype. The inhibition of lymphocyte proliferation by the testicular macrophage, its unique cytokine profile, high basal production of GM-CSF and prostaglandins, and the refractoriness to LPS all suggests a role that contributes to the immune privilege that is afforded the testis. However, these aspects of testicular macrophage immuno-biology also support a role in local cell-cell communication and regulation of the normal physiology of the testis, and macrophages may be directly involved in Leydig cell steriogenesis. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Science, 1997?