Regulating Mechanisms of Gonadal and Pituitary Tumorigenesis in Mice Producing Human Chorionic Gonadotropin

Human chorionic gonadotropin (hCG) and luteinizing hormone (LH) are structurally and functionally similar glycoprotein hormones acting through the same luteinizing hormone chorionic gonadotropin receptor (LHCGR). The functions of LH in reproduction and hCG in pregnancy are well known. Recently, the expression of LHCGR has been found in many nongonadal tissues and cancers, and this has raised the question of whether LH/hCG could affect the function or tumorigenesis of these nongonadal tissues. We have also previously generated an hCG expressing mouse model presenting nongonadal phenotypes. Using this model it is possible to improve our understanding of nongonadal action of highly elevated LH/hCG. In the current study, we analyzed the effect of moderately and highly elevated hCG levels on male reproductive development and function. The main finding was the appearance of fetal Leydig cell (FLC) adenomas in prepubertal males. However, the development and differentiation of FLCs were not significantly affected. We also show that the function of hCG is different in FLCs and in adult Leydig cells (ALC), because in the latter cells hCG was not able to induce tumorigenesis. In FLCs, LHCGR is not desensitized or downregulated upon ligand binding. In this study, we found that the testicular expression of two G protein-coupled receptor kinases responsible for receptor desensitization or downregulation is increased in adult testis. Results suggest that the lack of LHCGR desensitization or downregulation in FLCs protect testosterone (Te) synthesis, but also predispose FLCs for LH/hCG induced adenomas. However, all the hCG induced nongonadal changes observed in male mice were possible to explain by the elevated Te level found in these males. Our findings indicate that the direct nongonadal effects of elevated LH/hCG in males are not pathophysiologically significant. In female mice, we showed that an elevated hCG level was able to induce gonadal tumorigenesis. hCG also induced the formation of pituitary adenomas (PA), but the mechanism was indirect. Furthermore, we found two new potential risk factors and a novel hormonally induced mechanism for PAs. Increased progesterone (P) levels in the presence of physiological estradiol (E2) levels induced the formation of PAs in female mice. E2 and P induced the expression and nuclear localization of a known cell-cycle regulator, cyclin D1. A calorie restricted diet was also able to prevent the formation of PAs, suggesting that obesity is able to promote the formation of PAs. Hormone replacement therapy after gonadectomy and hormone antagonist therapy showed that the nongonadal phenotypes observed in hCG expressing female mice were due to ovarian hyperstimulation. A slight adrenal phenotype was evident even after gonadectomy in hCG expressing females, but E2 and P replacement was able to induce a similar phenotype in WT females without elevated LH/hCG action. In conclusion, we showed that the direct effects of elevated hCG/LH action are limited only to the gonads of both sexes. The nongonadal phenotypes observed in hCG expressing mice were due to the indirect, gonadal hormone mediated effects of elevated hCG. Therefore, the gonads are the only physiologically significant direct targets of LHCGR signalling.

Behavioral Responses in Mice Selectively Bred for High and Low Levels of Open-Field Thigmotaxis

In animal psychology, the open-field (OF) test is a traditional method for studying different aspects of rodent behavior, with thigmotaxis (i.e., wallseeking behavior) being one of the best validated OF parameters employed to measure emotionality. The main purpose of the present study was to investigate the selection response in mice selectively bred for high and low levels of OF thigmotaxis (the HOFT and LOFT lines, respectively). The mice (N = 2048) were selected for 23 generations, resulting in bidirectional phenotypic divergence between the two lines; that is, the HOFT mice were more thigmotactic (i.e., more emotional) than the LOFT mice across the different generations. The origin of the line difference in thigmotaxis was further investigated by using the crossfostering paradigm, with the results suggesting that the divergence between the two lines was primarily innate in origin and not influenced by differing maternal behavior. The stability of the selection trait was examined by testing the animals at different ages as well as in varying conditions. The results indicated that the line difference in thigmotaxis was not affected by age at the time of testing, and it also persisted in the different OF testing situations as well as during pregnancy and lactation. The examination of a possible coselection of other characteristics revealed that the more thigmotactic HOFT mice lived longer than the less thigmotactic LOFT mice. In addition, the HOFT mice tended to rear and explore less than the LOFT mice, supporting the general assumption that emotionality and exploration are inversely related. The two lines did not generally differ in ambulation and defecation, that is, in the traditional OF indexes of emotionality, conforming to the suggestion that emotionality is a multidimensional construct. The effects of sex on different OF parameters were also assessed, with the results suggesting that among the HOFT and LOFT lines, the female mice were more emotional than the male mice. The examination of the temporal changes in the HOFT and LOFT lines’ OF behavior revealed some contradictory findings that also partially conflicted with general assumptions. Although this study did not show prominent differences in maternal responsiveness between the HOFT and LOFT mothers, the results suggested that the line divergence in emotionality was more pronounced in the presence of a pup after parturition than during pregnancy. The present study clearly demonstrates that OF thigmotaxis is a strong characteristic for producing two diverging lines of mice. The difference in thigmotaxis between the selectively bred HOFT and LOFT mice seemed to be a stable and robust feature of these animals, and it appeared to stem from a genetic background.

JNK regulation of neurogenesis, neuroplasticity and anxiety-related behaviors in mice

I vår moderna värld har förekomsten av ångeststörningar drastiskt ökat, vilket påverkar välfärden i våra samhällen. Eftersom de molekylära mekanismerna bakom ångest är relativt okända, är möjligheterna till behandling av ångeststörningar begränsade. I och med utvecklingen av genetiska manipuleringmetoder och avbildningstekniker har strukturella förändringar associerade med ångeststörningar kunnat konstateras. Neuroanatomiska studier har påvisat störningar i dendritarkitektur, dendrittaggar och i neurogenesen hos vuxna individer. Särskilt neurogenesen i hippocampus anses viktig i detta sammanhang. Neurogenes i hippocampus har föreslagits spela en viktig roll i ångeststörningarnas patofysiologi och för hur vissa antidepressiva läkemedel förmedlar sin effekt. Under senare år har MAP-kinaser (MAPK) föreslagits vara involverade både i uppkomsten av affektiva störningar och i neurogenes i hippocampus. JNK är en grupp kinaser inom MAPK-familjen som aktiveras av olika externa stressfaktorer. I normala celler är aktiviteten hos JNK låg. Cell-stress ökar aktiviteten hos JNK vilket leder till bl.a. apoptos. JNK kinaser anses vara potentiella terapeutiska mål för behandling av neurodegenerativa sjukdomar men deras potential som mål för behandling av affektiva sjukdomar har tillsvidare inte utretts. Den här avhandlingen behandlar betydelsen av JNK för ångestrelaterat beteende hos möss. Med hjälp av Jnk1-knockout möss och farmakologisk inhibering av JNK-signalering, demonstreras att JNK reglerar neurogenes i hippocampus, vilket i sin tur ligger bakom mössens ångestrelaterade beteende. Jnk1-knockout möss var mindre ängsliga och uppvisade ökad neurogenes i hippcampus jämfört med kontrollmöss. Inhibering av JNK-signalering i hjärnan hos möss gjorde dem också mindre ängsliga och ökade neurogenesen i hippocampus på samma sätt som vissa antidepressiva läkemedel. Inhibering av JNK-aktivitet ledde inte bara till ökad neurogenes i hippocampus, utan främjade också mognandet av nybildade nervceller hos vuxna möss. Resultaten visar också att dendritarkitekturen och fördelningen av dendrittaggar hos CA3 neuroner i hippocampus är förändrad hos Jnk1-knockout möss. Genom screening av substratmolekyler för JNK hittades två JNKeffektormolekyler, MARCKSL1 (ett aktin-associerat protein) och MAP2 (ett mikrotubulus-associerat protein), som reglerade neuronernas sttruktur. Det här tyder på att JNK-signalering kan kontrollera ångeststörningsrelaterade förändringar hor dendriter och dendrittaggar. Sammanfattningsvis ger resultaten som presenteras i avhandlingen en ökad insikt i molekylära mekanismer som kan leda till ångeststörningsrelaterade förändringar i neurogenes och dendritstruktur. Därtill föreslås att JNKsignalbanan har potential som terapeutiskt mål för behandling av ångeststörningar.