It does not rain us on the fact that androgens are the main culprits, however we must observe the conditions in which they act. I do not think it is optimal to discard prolactin a priori, it still has links with the immune system and above all with cellular quiescence.
The thing that really seems strange to me at the outset is how it is possible that the hair follicles even after many years of baldness progression are still present, almost as if in standby, waiting for something to reactivate their paths, halfway between death and the resurrection, until obviously time runs its course. This view may seem "anthropomorphic" but I seriously think that nature does not preserve something that supposedly causes problems, does not stop the processes of heralded death, then baldness can really be something accidental on the same level as a tumor or an autoimmune disease.
Androgens in the upper part of the head are found in a very particular part of the tissue, in hypoxia.
We temporarily remove androgens from speech, in hypoxic conditions a transcription factor called HIF1α comes into play, an element that, in synthesis, allows cells to adapt to the absence of oxygen.
https://www.nature.com/articles/s41580-020-0227-y
en.wikipedia.org
“
HIF1α expression in
haematopoietic stem cells explains the quiescence nature of
stem cells for being metabolically maintaining at a low rate so as to preserve the potency of stem cells for long periods in a life cycle of an organism.
The HIF signaling cascade mediates the effects of hypoxia, the state of low oxygen concentration, on the cell. Hypoxia often keeps cells from
differentiating. However, hypoxia promotes the
formation of blood vessels, and is important for the formation of a
vascular system in
embryos and tumors. The hypoxia in
wounds also promotes the migration of
keratinocytes and the restoration of the
epithelium. It is therefore not surprising that HIF-1 modulation was identified as a promising treatment paradigm in wound healing”
At this point I ask myself: what if baldness was just a path of cellular “lethargy” induced in response to some conditions present on the top of the head? Given some conditions / pathways, HIF1α is prevented from doing its job, on the other hand HIF1α, necessarily present, although decreasing over time, ensures that a metabolic maintenance of the stem cells is preserved, at least as long as this is possible, after the follicles go on permanent standby until they die completely. Probably the reason why miniaturization can take a long time depends on this, even the fact that baldness does not immediately take place with puberty can be indicative.
Hypoxia-inducible factor 1 (HIF1) is a master transcription factor that induces the transcription of genes involved in the metabolism and behavior of stem cells. HIF1-mediated adaptation to hypoxia is required to maintain the pluripotency and survival ...
www.ncbi.nlm.nih.gov
https://pubmed.ncbi.nlm.nih.gov/33326985/
This explanation lacks the main protagonist of baldness: DHT. So what role does DHT play in relation to hypoxia and especially HIF1α?
From this research it seems that in conditions of hypoxia DHT inhibits the expression of HIF1α ..
https://pubmed.ncbi.nlm.nih.gov/21856910/
But the curious thing is that in the presence of few androgens (so we can assume that this happens in pre-adolescence) and in hypoxic conditions HIF-1α favors the expression of the androgen receptor, probably this is the moment in which the process begins.
https://www.sciencedirect.com/science/article/abs/pii/S0960076010003602
Here reference is made to general organisms, and this may coincide with the fact that all men (even those with a perfect hairline) have less hair on the top of the head, but based on some predispositions that only a few need to be investigated (however a majority) develop baldness before actual old age.
It is as if HIF1α decrees its own disappearance, which in cases of baldness occurs totally or in any case much faster than the others. This is where genetics come into play which is something I haven't addressed yet.
This may be the origin of the androgen paradox, which if we think about it is not so paradoxical if we take into account the different conditions in which the hair follicles are found. With adolescence, we usually develop hair in the areas most supplied with blood and oxygen: face, chest, etc. generally someone appears slightly balding, in conditions of predisposition in the scalp a sort of hypoxia could form without any advantage: neither vascularization occurs and given the increasing presence of androgens HIF1α (which would allow the natural metabolism of stem cells) is inhibited more and more.
Referring back to what pegasus2 said in the first answer to my comment, I re-launch my hypothesis by trying to expand: dht stimulates growth in hypoxic conditions, this is therefore valid in vitro at a general level; but in vivo, and precisely in the scalp destined for baldness, this growth is likely to have gone mad: dht continuously stimulates hair growth but at the same time inhibits the expression of HIF1 which is necessary in hypoxic conditions for stem cells continue to perform their functions - the cells probably do not feel hypoxic due to the inhibition of HIF1α and therefore continue to produce DHT to maintain the hair growth function as if they were in another area of the body - it is like building a building without a foundation: the cells cannot keep up and cannot carry out their metabolism, the hair cycles become faster and faster until you get hair so fine that it is imperceptible, all this is a vicious circle because if HF1 on the one hand protects (as long as it can) the hair follicles and ensures a minimum sustenance - the minimum to generate ever finer hair - on the other hand, the expression of AR increases and since he is inhibited by the dht he decrees his slow suicide: a sort of civil war.
The Dht also inhibits the wnt path.
Before getting to prolactin, however, I would like to open a parenthesis that intrigued me a lot between hypoxia, glucose absorption and insulin resistance. In the condition of hypoxia the tissues tend to balance the lack of oxygen with more ways, as well as through the transcription factor that I have mentioned several times, the tissues tend to vascularize but above all to cause the cells to absorb more glucose.
Well in baldness we have established that the first phenomenon does not exist or that it is so scarce as to be irrelevant (I don't know if this has ever been investigated through methods that did not involve minoxidil) but what intrigued me is precisely the absorption of glucose :
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4144211/
Premature baldness has a fairly strong correlation with the metabolic syndrome of insulin resistance, which could be due to the cases of premature baldness that are increasingly present today. The Western diet is now characterized by the extreme use of sugars. Asians are getting there but until recently their diet was very varied and not excluding much more relevant genetic factors it is possible that the few cases of baldness are due precisely to a healthier diet (from this point of view) maintained in the over time.
This makes me increasingly think that hypoxia in the scalp of balding people is much more serious than the physiological one, there are mechanisms that prevent physiological adaptations
so we come to prolactin
https://www.sciencedirect.com/science/article/abs/pii/S0304394099009684
This study (unfortunately on rats) seemed interesting to me especially in the final.
This perhaps explains why it is important to inhibit prolactin before the aromatase in the scalp is definitively over, so when we still have some hair
Estrogen and prolactin play important role in mammary carcinogenesis. The present study was undertaken to evaluate the effect of prolactin and estrogen cross-talk on HIF-1 α level and expression of some HIF-1 α- dependent signaling proteins. Since up-regulation of prolidase activity inhibits...
pubmed.ncbi.nlm.nih.gov
In the presence of Estradiol, prolactin inhibits HIF1α, therefore removing the prolactin increases HIF1α and the possibility that the cells maintain their metabolism. This may be related to the path of apoptosis that prolactin activates and at the same time may explain why in some cases it helps hair growth and in others it decreases it. Following my reasoning, there should be an element in the inhibition of prolactin that determines one of these four possibilities or perhaps combinations:
- The scalp comes out of the hypoxic condition in such a way that the dht acts as with all other body hair or at least reduces its negative effects
- Increase of aromatase up to genuine levels that ensure proper cell proliferation (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3672802/)
- For a series of mechanisms that I should investigate in the future, the inhibition of prolactin slows down / clears the process of cell madness in hair growth, creating a sort of respite (this could be linked to BMP4)
- End of the apoptosis process
Here I feel like self-criticism: I have not found studies on prolactin related to hypoxia, the only ones are these that concern women, and even if the factors, proteins and compounds are universal, it is possible that there are misunderstandings.
I also need to ascertain whether there is still a significant amount of estradiol in the bald scalp that could explain the second prolactin study.
For now I feel like HMI alone will probably not work because there will be other paths to correct first, my hope is of course that it works as well as it did with those monkeys.
Even the fact that it worked on monkeys should not be negatively accepted, it is true that monkeys could be like mice in this area, but it is still an empirical confirmation not just, all the possible links that prolactin remain to be found has with the process of baldness.
Hormone therapy is successful because it eliminates androgens from the equation in a certain sense, silences most of the negative effects, estrogens are directly connected with aromatase and in addition to favoring it, they protect it from the effects of androgens, all this in fact me seems connected, you just need to better understand the "backup" and interaction paths with some structural characteristics of the environment (only this in my view can explain the pattern of baldness and possibly the different level of severity of it)
The majority of postmenopausal breast cancers are estrogen-dependent. Tumor-derived factors, such as prostaglandin E[2 ] (PGE[2] ), stimulate CREB1 binding to cAMP response elements (CREs) on aromatase promoter II (PII), leading to the increased expression ...
www.ncbi.nlm.nih.gov
I think that if you stop the hormonal therapy, you go back to the starting state even if it is slowed down.
I have linked studies that do not necessarily have to do with baldness and the scalp, however they seem to me to be good starting points for understanding how the mechanisms work. There must be something in the environment determined at the start or by the follicle cells themselves at a certain point in their path, it is natural that the paths are influenced by the environment in which they occur, by factors such as: the presence of some metabolites, the concentration, the mechanisms of passage between membranes, etc. etc. Let me know what you think.