stirrhs (en) - Expression of androgen- and glucocorticoid-related genes during saccular and alveolar stages of mouse lung development - Comments

Great discussion! Have some

de-vrijerb — Thu, 26 Mar 2009 13:43:29 -0400

Great discussion!
Have some true transdisciplinary research anyone interested in sex differences (and studying it) should read: the book(!) is called 'Dr Tatiana's sex advice to all creation' written by Olivia Judson. Fun to read - but it also may change your views on which is the 'vulnerable' and which is the 'strong' sex... confusingly little to do with our social values!

Think about this:
If males are meant to hunt, fight and protect (when we still lived in caves with dinosaurs around) what is the use for the 'runt' or the 'defective' male? If he is not strong - perfectly healthy - he's just another mouth to feed and should not survive - he's potentially only detrimental to the tribe (and he should definitely not be allowed to procreate and mix his weak genes in the genepool!). That may explain a bit of the (initial) male disadvantage in life. For instance - men may have sepsis less frequently but when they do, it is more likely to be severe and they are more likely to die as the consequence of it than women are. It may all be the result of (a androgen effect on) differences in immune system, and higher levels of interleukins are measured in immune challenged males, both in adult life as well as in fetal life (ongoing work). This may be an indication of a 'fight' response so strong that you either come out well (ie. completely intact) or die - but no in between with disabilities.
Women can be quite usuful even if they are not entirely healthy - as long as they can still breed or take care of children - and also need a less strong immune system to be able to tolerate a pregnancy. So they benefit from not fighting too hard and maybe giving up a limb or so in the process.

Then finally, what we (cavewomen) did in our cultural model favouring male offspring is probably more related to the potential to spread our genes - a male can have an infinite number of offspring, while in a female it's limited - to 20 or so (wonder what the record is!) - so for a parent is is advantagous to have a boy - if he's successful (in getting as many girls pregnant as he can) your genes have spread!

I am sure this too is a very simplified version of why responses are really different, but it may be a start to modify your thought process: read the book, I am sure you'll find more!

Barbra

Thanks Eric! That was a

mcintyre — Fri, 06 Mar 2009 13:36:41 -0500

Thanks Eric! That was a very thoughtful discussion. Best of luck with your project and future endeavors! :)

Hi Martin, I really enjoy

boucher — Thu, 05 Mar 2009 19:33:58 -0500

Hi Martin,
I really enjoy reading your questions. I hope my answers will shed some light onto them.

Q: With regard to multiple versus single courses of antenatal glucocorticoids in fetuses at risk of preterm labour, are you aware of benefit studies accounting for fetal gender?
A: I’m not aware that there have been any studies showing differential outcome of single vs single courses of antenatal glucocorticoids in males or females. My understanding is that the principal interest for multiple courses comes in the fact that the efficiency of the single dose is limited to about 4 to 7 days after administration. This is a problem when labour is successfully arrested for more than 7 days, after the initial glucocorticoids treatment. The problem with multiple doses is that is increases the chances of neurodevelopmental damages or HPA axis reprogramming, compared to a single dose.

Q: Could it be that due to 'androgen disadvantage' male fetuses in fact would show lower rates of RDS if administered multiple glucocorticoid courses?
A: Male foetuses do show lower rates of RDS, even with single doses. The problem is that they show higher rates than treated females. This suggests that the sex difference is established before glucocorticoids action can take place. As such, even if they have “more catching up to do” then females, I do not think that multiple doses will result in equal rates of rates of RDS in males and females, females will still have lungs that are more mature than males.

Q: Gender differences have been described for chemo- and baroreceptor sensitivity. Since these systems are relevant for RDS, I wonder to what extent they may also contribute to its higher prevalence in males.
A: I’m not aware of any studies that have looked at this directly, but it certainly could be a contributing factor. It might be implicated in the higher rates of ventilation induced BPD in boys compared to girls. Very interesting idea, I’ll certainly look into it in more detail and introduce it to the discussion forum.

It was suggested by Doan et al. 2004, that 'estradiol secreted during late gestation is necessary for respiratory adjustment to pregnancy and is required for adequate development of respiratory and metabolic control in the offspring'.
Joseph et al., 2000, wrote that ‘GENDER-RELATED DIFFERENCES in the physiological responses to hypoxia have been reported by several studies that demonstrated a better capacity of women and female rats to adapt to hypoxia.'
Q: As such, should one consider early postnatal administration of estradiol and/or progesterone to male neonates?
A: Very interesting idea! Estradiol has indeed been shown to accelerate lung development. I’ve found a couple of very promising papers that explored this line of treatment. For exemple, in a baboon model of BPD, McCummin et al 2009 found that post-natal Estradiol treatment upregulated nitric oxide synthase, resulting in “favorable cardiovascular impact, enhanced pulmonary function, and lowered requirements for ventilatory support”. Of course, the benefit of such a treatment should be weighed against the obvious possible detrimental sexual development effects. I’m also sure that females would equally benefit from this avenue.

Again, thanks for the very thought-provoking insights!

Eric

Hi, Thanks for your

boucher — Thu, 05 Mar 2009 18:14:45 -0500

Hi,

Thanks for your additional input Martin.

Eric

Hi Alex, To answer your

boucher — Thu, 05 Mar 2009 18:12:00 -0500

Hi Alex,
To answer your question, as to when the male vulnerability changes genders, I do not think it really ever does, at least biologically. For example, men (in general, not only preemies) are more prone to a lot of diseases common to both sexes than women (ex.: cardiovascular, certain types of cancers, ect.), boys starts puberty later in life than girls and men have shorter life expectancy than women. Psychosocial factors such as increased risk taking, diet, increased alcohol abuse and decreased help-seeking certainly increases those discrepancies, but many biological factors impact males more negatively than females(ex.: testosterone levels, x-linked diseases). That being said, they are certainly many examples where females are at a biological disadvantage (ex.: hormone sensitive cancers, reproductive health, etc) or socially negatively biased. A more complete answer would then be that the gender vulnerability changes with psychosocial and biological context of the individual.

Your example concerning alcohol abuse struck my interest, as I found that the answer was a lot more complex then I first anticipated. I first thought that the higher sensitivity of women to alcohol was mainly explained by the fact that they are in general smaller than men, or by a difference in habit. After a quick literature search, I’ve also found that women might be innately more sensitive to the effects of alcohol than men (ex.: partly reviewed in Hommer 2004, Alcohol Research & Health vol 7, No 2 pages 181-185.). Thanks for the question, excellent example of sex and gender based research!

If there’s indeed a sex-bias in favour of treating male preemies more aggressively than females, this could be paradoxically participates in the poorer outcomes seen in males, as some of the more aggressive treatments in premature infants care, can have negative long-lasting consequences (Ex.: respiratory, neurodevelopmental, etc). This is a perfect example of a psychosocial factor directly influencing biological outcomes and underscores the importance of the transdisciplinary approach.

Thanks,

Eric

Hi Eric, Interesting

mcintyre — Thu, 05 Mar 2009 11:42:02 -0500

Hi Eric,

Interesting thoughts re: gender differences - thanks! In my line of work where we see patients as grown adults it is very difficult to tease apart biological vs. psychosocial causes of gender differences. I guess I am struck by how easy it is to identify testosterone as the main contributor to the gender differences that you study.

I guess I find it striking that male infants are more at risk than female infants, generally speaking, as we find that men to have more robust systems as adults. I'm thinking about things like substance use here - women tend to be more sensitive to the effects of alcohol than men, for example. Also I think that it is very interesting to see a male vulnerability in utero just given our somewhat outdated yet still prevalent notions of gender roles of males as strong providers and women was passive nurturers. I know it's a long way off from your research, but not being an expert in your area, I do find the male disadvantage to be striking compared to how we generally view men vs. women. When does this vulnerability change genders? Or does it really?

I think this links up with your question about sex-bias concerning the length or aggressiveness of the treatments pursued for male vs. female infants. I'm assuming the advantage is for males in that case. I'm thinking specifically about Dr. Nisker's presentation at the transdisciplinarity conference in Montreal where he talked about parents wanting to be able to select for male children in utero. Isn't it interesting that there is a preference for males for social reasons but for purely viability reasons, females may be the better choice?

Thanks again for your great presentation and thoughtful remarks. I've appreciate thinking about this.

Alex.

Hello Eric and thank you for

frasch — Thu, 05 Mar 2009 00:18:45 -0500

Hello Eric and thank you for sharing your work!

With regard to multiple versus single courses of antenatal glucocorticoids in fetuses at risk of preterm labour, are you aware of benefit studies accounting for fetal gender?
Could it be that due to 'androgen disadvantage' male fetuses in fact would show lower rates of RDS if administered multiple glucocorticoid courses?

Gender differences have been described for chemo- and baroreceptor sensitivity. Since these systems are relevant for RDS, I wonder to what extent they may also contribute to its higher prevalence in males.

I found this study on the effects of testosterone on IUGR and gender-dependent postnatal catch-up growth interesting:
PMID: 14576190

Hope you find some of this useful.

All the best,
Martin

Hi Heather and Eric, just to

frasch — Wed, 04 Mar 2009 20:35:11 -0500

Hi Heather and Eric,

just to add in and address your question more generally: fetal sheep was the model in which 1969 Liggins described effects of antenatal glucocorticoids on lung maturation. Ever since it has served on multiple levels: for studies of cardiovascular and endocrine control as well for studies of fetal brain development under various acute and chronic hypoxic/asphyxic/IUGR conditions with and w/o glucocorticoids. Also, issue of multiple versus one time course of glucocorticoids was addressed with regard to their effects on fetal brain (briefly: rather unfavourable) and on lung maturation suggesting no added benefit from multiple courses.
Fetal sheep brain has white matter and stage of development similar to the human fetal brain in late gestation. This makes it a very good model of various aforementioned pathophysiologies. Rodents do not really have white matter. Preterm neonates are at risk of white matter injury probably due to immmature oligodendrocytes and this cannot be modeled in rodents. Also with respect to the ratio of fetal and maternal weights at birth as well as growth dynamics in utero (long gestational period) ovine fetus is a very good approximation of humans.

Martin

Hi Heather, Foetal lambs are

boucher — Wed, 04 Mar 2009 18:02:18 -0500

Hi Heather,

Foetal lambs are used to study the effect of antenatal glucocorticoids treatment (doses, multiple vs unique, etc), but their use is now mainly restricted as surgical models for diaphragmatic hernia, which causes lung hypoplasia and surfactant deficiency and on inflammation-linked lung maturation. It was also in the sheep (lamb) that most of the studies on tracheal occlusion were first initiated. Tracheal occlusion is one of the proposed treatments to accelerate lung maturation in diaphragmatic hernia patients (almost only used as an experimental model), but is also used to study the impact of mechanical stretching on lung maturation. The advantages of the sheep in this context are size (because of the surgeries) and the time-scale that are closer to that of human lung and foetal maturation. I’ve looked at a couple of papers and most of the times the strain was not mentioned (probably because strains of lambs are less defined than other models such as mouse, rat, rabbit or guinea pig).

Thanks again for your comments.

Eric

Thanks Eric, After reading

Allaway — Wed, 04 Mar 2009 10:33:55 -0500

Thanks Eric,

After reading your answers to my questions I re-read your presentation and was better able to understand the outcomes. Thank you for your quick response and detailed answers.

I know that different domestic species are used as models for different reasons. Bovine and equine are used as ovarian dynamic models and porcine are used in disease and tissue transplant experimentation. I was wondering what makes sheep a good model for human fetal development? I have read some papers on ovarian dynamics in sheep which show that some breeds regularly have twins due to a static phase of one dominant follicle as the next dominant follicle begins to grow so I was wondering is it all breeds or just a couple that work as models?

Heather

Hi Alex, Thanks for your

boucher — Tue, 03 Mar 2009 21:46:44 -0500

Hi Alex,
Thanks for your questions.
1)
Q :Why does it seem to be the case that male fetuses are more at risk than female fetuses? Not being an expert in your field, I have noticed this trend among a few of the STIRRHS presentations to date. Is this vulnerability thought to be linked solely to testosterone levels or to a combination of factors? I find it curious as in my line of work, which focuses more on psychosocial stressors and HIV transmission, we often perceive women to be more at risk. Any thoughts you have would be greatly appreciated.
A : The male disadvantage (at least for lungs and RDS) is pretty much only linked to higher testosterone levels. Androgens have been shown to delay the surge of surfactant (a complex lipid and protein secretion necessary to normal lung function that act by lowering the surface tension of the alveoli, which in turn prevent their collapse). This has been demonstrated in a number of animal models. What remains unclear is how the punctual increase in the levels of testosterone associated with testicular differentiation, which occurs several weeks (days in mouse) before surfactant production, causes the delay in lung maturation. Also, at the same gestational age, some male fetuses fair far better than females (opposite to the statistics). This suggests that there must be other biological factors at work here... My project studies lung maturation, but prematurely born boys are also behind girls for other system as well, that also contribute to their poorer general outcome. As for a psychosocial factor, I’m not aware that extreme premature males have any disadvantages at the onset, other than they usually have a poorer diagnostic. The graduate student responsible for the psychosocial section of the discussion forum did point out that infants born prematurely show more cognitive and social problems at almost all the ages studied, and that boy were more affected by those problems than girls. Whether this male disadvantage is specifically due to the poorer outcome of premature boys, reflects the higher prevalence of those problems in boys in the general population or results from a specific psychosocial male disadvantage is still unclear in the literature and was the subject of debate during the multidisciplinary phase of our forum. What do you think? Another question that was raised during the forum was the existence of a sex-bias (positive or negative) concerning the length or aggressiveness of the treatments that the parents are willing to put their offspring trough. Do you think that this exists? Do you think it could be responsible for a male disadvantage in mortality or morbidity?
I think you figured it out already, but the forum did give me insight into my project. There are A LOT of places where are STILL in the process of formulating a consensus opinion. That’s probably what I find both the most challenging and what I get out the most of.
Eric

Hi Heather, Thanks your

boucher — Tue, 03 Mar 2009 20:14:37 -0500

Hi Heather,
Thanks your questions and your comments. I agree that I have to be very cautious when transferring towards the clinic. Results in mice, rat or rabbit should indeed be seen as preliminary to lager studies or studies done in sheep (preferred in lung developement compared to pork) or in human.

1. Q :What are the characteristics of the Balb/C mouse strain? Which of the characteristics was important in your choice to use the strain as your model animal?
A : The Balb/C strain was chosen for two main reason. First, it is a inbred strain which as the advantage of high genetic homogeneity. This greatly reduces inter-litter and inter-individual variability. Second, it was in this strain that the sex-difference in the surfactant surge was the most extensively studied (papers by Nielsen in the late 80’s to mid 90’s). Since my project is the logical progression of those results, we decided to continue using this strain.

2. Q: You said "The increased number of sample and genetic homogeneity allows us to look for a possible sexual dimorphism of androgen or glucocorticoid regulation by the developing lung". How did you increase the sample number and the genetic homogeneity?
A: Thank you for pointing that out. Re-reading it, I also find the phrasing a bit confusing...
I was talking about an increased number of samples compared to what I would have been able to collect if I was working with human samples. As you surely realize those samples are extremely hard to come by, even with a protocol that has been approved by an ethics committee. The use of a mouse model also allows us to collect lung representing a higher number of days (intermediates between development stages) and to study terminal lung development in its entirety. That would have been impossible in human or other models such as rabbit or sheep. As I have explained in my response to your first question the Balb/C is an inbreed strain with high genetic homogeneity, especially compared to a human population.

3. Q: Why did you choose the five housekeeping genes you did for studying normalization? Do they have any significance in lung maturation?
A: The five housekeeping genes chosen for normalization do not have any significance in lung maturation. In fact we chose them exactly because they are not implicated in lung maturation. They were chosen because they because they have been shown to be stably expressed in a variety of tissues and under many conditions, which makes them good normalization gene candidates. Also, they represent different levels of expression (low copy number to high copy number). Without going into details, in QPCR, genes that are expressed at a low level are more susceptible to biases than genes expressed at high levels. Since some of our studied genes are expressed at low levels (ex.:17b-HSD2), we needed to included housekeeping genes that also are expressed at low levels in the calculation of our normalization factor.

4. Q: Other than lower basal corticosterone levels, what is associated with the stress hyporesponsive period?
A:The principal characteristic of the SHRP is the hyporesponsiveness in response to stress in regard to corticosterone and ACTH production. The SHRP is also characterise by high expression of CRH in the hypothalamus (paraventricular nucleus) and a steady increase of GR in the Expression levels of GR in the hippocampus until the end of the period.

Q:Is there a similar period observed in extreme premature infants?
A: Excellent question! As far as I know, there is no SHRP in human, at least human babies born at term have fully functioning HPA axis. Developement of the HPA axis is still the subject of investigation, but I will go back and check the literature to see if a similar period exists during the same lung development stages. I’ll try to get back at you before Thursday.

Hi Eric, Thanks for your

mcintyre — Tue, 03 Mar 2009 17:08:35 -0500

Hi Eric,

Thanks for your nice summary. I just have some bigger picture questions and thoughts about your research.

1) Why does it seem to be the case that male fetuses are more at risk than female fetuses? Not being an expert in your field, I have noticed this trend among a few of the STIRRHS presentations to date. Is this vulnerability thought to be linked solely to testosterone levels or to a combination of factors? I find it curious as in my line of work, which focuses more on psychosocial stressors and HIV transmission, we often perceive women to be more at risk. Any thoughts you have would be greatly appreciated.

2) How has your participation in the interdisciplinary discussion forum (on the impact of infants' sex at the limit of viability) shaped your approach to your work. Have you gained various insight into your own project or found places where you disagree with others?

All the best with your research!
Alex.

Factors such as gestational

boucher — Tue, 03 Mar 2009 15:46:48 -0500

Factors such as gestational age, birth weight and foetal sex are good predictors for the health outcome of extreme premature infants, but individuals tend to respond differently to antenatal and postnatal treatments, presumably because of difference in lung maturation. As such, a cocktail of markers (ex.: high 3aHSD, low 17b-HSD2 and high AR levels) evaluating the level of maturity of different aspect of the lung would be useful in order to “tailor” treatments to each infant, in order to minimize negative sequellea. The stages of developement in my study (saccular to alveolar) are the stages at which extreme premature infants receive treatment. Learning more about androgen and glucocorticoid action and metabolism in the murine lung at those stage, could provide insight on the potentially different timing of the glucocorticoid treatment premature infants according to their sex. The difficulty in the application of mouse data to a clinical setup lies with the availability of the material. With the exception of the L/S ratio and PG content in the amniotic fluid, most of the remaining biological markers of lung maturation developed in animal models (i.e.: rat, mouse, lamb) requires lung tissue, which cannot be obtained from extreme premature infants. As such, most of the information learned in animal models of lung development is fundamental in nature and often cannot be applied directly to the bedside of extreme premature infants, but provide insight.

Hi Eric, Thank you for your

Allaway — Tue, 03 Mar 2009 11:30:57 -0500

Hi Eric,

Thank you for your presentation. I just had a couple questions regarding your project.

1. What are the characteristics of the Balb/C mouse strain? Which of the characteristics was important in your choice to use the strain as your model animal?

2. You said "The increased number of sample and genetic homogeneity allows us to look for a possible sexual dimorphism of androgen or glucocorticoid regulation by the developing lung". How did you increase the sample number and the genetic homogeneity?

3. Why did you choose the five house keeping genes you did for studying normalization? Do they have any significance in lung maturation?

4. Other than lower basal corticosterone levels, what is associated with the stress hyporesponsive period? Is there a similar period observed in extreme premature infants?

To comment on the first question you posed to the group I do not necessarily believe the difference in environment completely invalidates the use of your mouse model. However, I do believe that during the knowledge transfer to novel treatments for the prevention of RDS you must be very cautious. The information gathered from the mouse model may allow you to focus the next study using larger animals whose lung development is complete in utero at term (ie porcine) and have shown to be a more reliable model for human development and disease.

Heather

Expression of androgen- and glucocorticoid-related genes during saccular and alveolar stages of mouse lung development

boucher — Sun, 01 Mar 2009 17:16:55 -0500

TITLE: Expression of androgen- and glucocorticoids-related genes during saccular and alveolar stages of mouse lung development
-1-RÉSUMÉ