This is a very interesting question. Although mice don't get very old, they still age and the question in stem cell biology frequently asked is: do stem cells age as well and loose their ability to work properly. Most stem cell niches seem to keep a constant number of stem cells and the HFSC compartment seems to be no exception. But does it become less potent?

"Reduced expression of stem cell markers" can mean several thing depending on how the reduced expression was determined. If you purified the cells (when it also depends on which markers you used and how you gated, basically what did you declare to be a HFSC) and compared young and old, then how much was it reduced? If you used in situ techniques and you saw it with your bare eye, then the reduction must be pretty dramatic but would still require some form of normalization to quantify the reduction. If you used whole skin or purified hair follicles, then how much did the non-stem cells contribute.

I assume you talk about purified populations. Then it depends how much of these markers you need to maintain their properties as stem cell factors. Many of the markers may be nothing more than markers and not relevant for the maintenance of the stem cells. Is the total stem cell marker package reduced, just selected markers? Is this a mouse thing or does this also occur in humans?

Another factor when using purified populations: how do you know how many hair follicles were in telogen? What stage and age was used for "young" and for "old".

Your finding is very interesting but hard to interpret without knowing how you came to the conclusion that the markers were reduced and what the function of these markers is. FOr Sox9 this is kind of known (I assume you meant Sox9 and not Sox2)for the others I don't think we have a clue. But in total your finding may indicate  a deterioration of stemness or at least how well it is preserved with age?

How is this in hematopoietic stem cells or crypt stem cells in mice with aging?

Exactly; markers may imply just an association and not necessarily cause-effect (sort of)  relationship.

Dear Dr.Thomas Andl.

Thank you for you detailed comment. The way we have investigated into the expression change in stem cell marker is usually F-IHC of the frozen section and quantify the intensity of the sub-bulge and bulge areas. In the case of HFSCs, the hair cycle is totally different between mice and human. Recently it has been published from  "Cell" which focuses on heterogeneous expression of c-Myc (c-Myc+/-) in mice leads to the disease-free longer longevity.  

Best Regards.

Go

I wanted to mention an incidental, probably relevant, fact. In our place, we have the belief, that hair grows more rapidly in the old age (may be it is a sort of lamp becoming more aflame before extinguishinh itself). This is true, and I dont know if it is a peculiarity of the tropics. I know, my (I am 60+ now) hair grows more rapidly than it did when I was young. Of course it is less dense due to sme permanent loss. Also, my earlobes have have hair which it did not, in the past. So is it possible that whatever hairfollicles remain grow faster in humans or rather the HSFC lose their stemness, and lose their characteristic of slow turnover, in old age?

Thank you for precious comment, Dr.Narayanan Bhattathiri.

In the case of mice, hair cycle is composed of anagen, catagen, telogen, and 1 cycle takes 1 month, so that in our lab we often remove hair in the telogen phase to reset and induce the proliferative anagen phase.

In contrast, the cycle of human hair is different depending on the location; i.e. on the head skin where anagen persists until the aging hair loss or the  trunk where almost always telogen persists.

The analysis of human samples, aged skin with hair loss tends to down-regulate the expression level of 17th (XVII) typed collagen, localized in the cellular membrane of HFSCs, but not in ECM. Some of researchers overemphasized the function of XVII-typed collagen in that the reduction of this membrane protein is mainly responsible for the loss of other HFSC markers and loss of stemenss. However, I doubt this theopry until the molecular machinery is revealed.

My knowledge of hair cell biology is not deep; only those we study for radiotherapy and chemotherapy. Even there we take it as a fact that hairloss occurs with both and there is not much one can do about it. But, I think your work opens up new areas for resarch in this context.

With fractionated radiotherapy, if the dose is sufficient, hair loss occurs in the treated area and this is almost always permanent, ? denoting that all HFSCells are dead. This is understandable since radiation induces damage to the proliferating compartment and there is recruitment from the stem cell compartment (the 4Rs of Raditherapy), and finally once all of them become proliferative, they all die out.

With Chemotherapy, which has systemic effect, hairloss is generalised. But what is interesting is most of the patients have regrowth of hair 3-6 months after treatment; more interestingly, the new hair is almost always more beautiful, in our patients.

Previously, I have never thought of why this should be so. But your discussions make me ask that question. Can it be because in some follicles (are their old hairs and young hairs in the same person?) all the stem cells die out or is it because old or 'weak' stemcells get killed?  Or are the surviving stem cells those that have 'passed a test of fire'? Has any one studied the HFSC pattern before during and after radio/chemotherapy? I think none knows even how to do research in this area.

This appears a very exciting and a very necessary area for your research, has a high potential for clinical application. By chance if you can find the mechanism and develop a cure (one that will not affect the anticancer effects), then your future is assured.

That is an interesting comment by Dr. Bhattathiri. I did not know that hair basically is killed off after radiotherapy. But one has to admit that the radiation is probably "extreme" locally compared to the chemotherapeutic concentration. And at least %FU does not show any hair growth effects at "normal" doses while others lead to complete hair loss.

Why does the new hair after chemo look better? I assume because it's all new while the hair on our scalp has mixed age. some is newer some is pretty old (was the cycle about 2 years in human scalp hair, 2 years of anagen?). So after chemo, all hair is basically the same age and brand new.

Has anyone ever checked what happened to the hair follicles in irradiated areas. Are they gone, became cysts, sit there in telogen? 

Dr. Yoshida, there is Myc in mouse or human hair follicles? Myc antibodies are notoriously bad. I think the paper you mention does not show a single Myc stain and therefore it is very hard to evaluate for which cells Myc might be important. There is a decent moue monoclonal from Santa Cruz Bio that works okay in human samples and gives similar results as 9E10.

As I mentioned, most of these HFSC markers are just markers, may or may not be relevant in the human condition (nice example is CD34, which is a human hematopoietic stem cell marker but not a mouse HSC marker. I hope I got this right; or check the "markers" for mouse colon crypt stem cells: there are hardly any data on their usefulness in human colon, are there?).

Dr. Narayanan Bhattathiri and Thomas Andl 

Thank you for the kind comments!

As compared with chemo, radiation Tx does not seem to affect the hair loss in the clinical settings, probably due to the threshold of dose of radiation for tissue stem cells to be damaged is much lower in HSCs than in HFSCs. After all, the critical side effect of radiation Tx is the pancytopenia. Furthermore, the susceptibility to IR seems to be heterogeneous depending on each hair follicle, thus IR exposure makes heterogeneous pattern; old hair shaft (with high threshold) and young shaft (with low IR threshold and again enter the hair cycle) and moreover no longer hair shaft is produced (exhaustion of HFSCs).

Dr, Andl,

As a graduate student, I have used Santa Cruz antibodies in the case of c-Myc and beta-catenin. The clone No, is 9E10 if I remember correctly. However, the researchers who insists on the up-regulation of c-Myc in HFSCs after 10Gy IR does not seem to be localized in the nucleus and they do not seem to use 9E10.

Micro-sized cysts surely appear after IR, but I have not yet identified the biological significance. Given that some of the cyst wall cells are positive for keratin1, "pseudo-differentiation" might be induced. 

Finally, but most importantly, I do not agree more with your last comment about the impact of stem cell markers. Unless the relationship between molecular machinery or signal transduction has been revealed, they are just markers; no more no less! We have to use "functional" HFSC markers in the same way I have done research as a graduate course on the cancer stem cell markers, CD44 and EpCAM.  

Sincerely

Go 

Dear Dr. Andl and Go,

I never thought that there was so much need-to-know information on hair follicles. I would suggest that you write up these and present it at a Oncology conference; I am sure that most Oncologists are unaware of this important and relevant area.

Pancytopenia is never a problem with radiotherapy, unless you give whole body radiation, the indication for which is rare now a days. Also, the effect of Radiotherapy is local; i.e., if you irradiate the chest, there won’t be any hair loss in the scalp. The type of radiation is important; with MV beams, the dose buildup is below hair follicle and hair loss in treated field may be minimal, but exit areas may get good dose. Also the dose affects. When CNS prophylaxis radiation is given, the hair loss is mild since only 20Gy or so is used. But, Dear Go, with doses above 50 Gy or so, there will be permanent hairloss in the treated area, but only there; and there wont be any pancytopenia.

I had done some studies on serial scrape smears from oral cancera, evaluated multi/micro/binucleation and found significant relation with tumour control. These are related to repopulation attempts by the cells, and how fast these appear indicate how soon and fast cells start dividing.

When we try to pul out our hair, it is painful; but with RT and Ct hairloss, the hair fall is painless. It may be that in these circumstances, hair can be pulled out, prior to their falling, with out any pain. I had long back thought of studying the hair follicle cytology using such hair follicles, but could not proceed due to other commitments.

This, I think is an area, where human studies can be done ethically, since most aptients would allow this because hair loss is imminent anyway. May be you can do all sorts of marker studies using these, and there are many many patients undergoing CT/RT. Dear Sirs, why not think of such a study?

One thing I forgot to add. The difference between Radiation and Chemo is that the effect of chemo, be it in hair follicle cells or others, will be influenced by the amount of drug the cells take up; may be somel HFScs do not get sufficient dose for damage, where as in the case of Radiation, since it is penetrative, the cell cant do anything about taking it up; it is automatically exposed if inside the treatment area. Another difference is that effect of radiation is much more cumulative than most drugs.

What I have written about the effects is from my own experience. I had more than thirty years of clinical practice and treated more than 15000 new cancers at least, before taking up my present vocation. Hair loss with RT is usually permanent

Thank you for your comment!

As you mentioned in details, side effect is different depending on the type of radiation Tx. The mechanism of the hair loss between human and mice might not be the same. IR-induced DNA damage response induces the dormant status of HFSCs???  

Hair loss due to chemotherapy or radiation seems to be different from aging-associated hair gray and loss. Senescent stem cells no longer exhibit cell division with up-regulation of cyclin kinase inhibitors such as p16, p19, and p21. Further, some of my data suggests the possibility that aged or radiation-damaged HFSCs show ectopic differentiation in the sub-bulge and bulge niche, move upwards in collective cell manner and discarded.