Hair loss is also related to it? Research has found that healthy cells can devour their companions' "corpses" to make hair follicles healthier
2024-08-27
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▎Edited by WuXi AppTec Content Team At this moment, some cells in our body will die due to aging and damage. If these dead cells are not removed in time, they will occupy the space of new cells and cause inflammation.Macrophagesare the cell types that are best at doing this, and they can resolve dying cells through phagocytosis.Although macrophages are found throughout the body, there are some exceptions, such asMacrophages are rarely seen in hair follicles.The hair follicles themselves are rapidly growing cells that undergo decline and regeneration. Faced with a large number of aging and dead cells, what mechanism can make up for the lack of macrophages?Recently, a paper in Nature magazine revealed the mystery.Many healthy stem cells also have the ability to engulf nearby dead cells, and their work capacity is no less than that of macrophages.Especially in hair follicles, the phagocytic function of healthy stem cells is very important for the homeostasis of the local environment. If only macrophages are relied upon for clearance, it will cause inflammatory damage and even affect the health of hair follicles in the long term, leading to problems such as hair loss and baldness.We can see hair falling out from tables, pillows, floor drains, etc. almost every day. This is because hair follicles go through a specific cycle, includingGrowth phase, catagen phase, and telogen phaseDuring the regression phase, hair follicles rapidly degenerate and gradually develop from the base of the hair follicles to the area where hair follicle stem cells (HFSCs) gather, during which a large number of cells die. If these dead cells are not removed in time, they will trigger local autoimmune reactions and inflammation, destroying the microenvironment of HFSCs and affecting the subsequent hair follicle cycle.To confirm the specific behavior of HFSCs in hair follicles, the authors observed mouse hair follicles at different stages of the hair cycle and unexpectedly found thatNot only are there fewer macrophages in the hair follicles during the catagen phase, but they also appear very late.Macrophages arrive four days after the hair follicle cells die.There are also potential clearance mechanisms that help deal with dying cells.The authors followed the hair follicles step by step and carefully observed the areas where HFSCs gathered, and found a phenomenon that was completely different from previous cognition. In the past, it was believed that when hair follicles were damaged, HFSCs would not be affected, but the new study found that this was not the case.Some HFSCs will also die during the regression period, and the nearby active HFSCs will choose to devour their dead neighbors., one HFSC can engulf up to 6 neighboring cells.▲Healthy HFSCs can engulf surrounding dead cells(Image source: Reference [1])According to the time sequence, in the early stage of hair follicle regression, the number of HFSCs involved in phagocytosis is equal to that of apoptotic cells, while in the late stage of regression, the number of HFSCs involved in phagocytosis has reached twice that of apoptotic cells. The authors found many apoptotic bodies inside these HFSCs, which may obtain molecules such as proteins, lipids and nucleic acids from dead cells.The accumulated resources can help HFSC start a new growth cycle later, which is crucial for hair regeneration.。In addition, healthy HFSCs do not perform phagocytic tasks at random. Before initiating phagocytic behavior, two receptors need to be activated, one calledRXRα, which detects some signals secreted by dying cells, such as lysophosphatidylcholine (LPC). When the authors blocked the production of LPC in apoptotic cells, HFSCs were unable to activate genes required for phagocytosis, including genes related to lysosomal function.RARγ, which senses retinoic acid secreted by healthy cells and mediates the response of RXRα.Only when both receptors are activated at the same time will the clearance and phagocytosis work begin, thus avoiding accidental attacks on other healthy cells.▲After the RXRα receptor is destroyed, HFSC will not engulf dead cells(Image source: Reference [1], credit: Robin Chemers Neustein Laboratory of Mammalian Cell Biology and Development at The Rockefeller University)The authors pointed out that if the phagocytic function of healthy HFSCs is destroyed and macrophages are completely responsible for the clearance work in hair follicles, the healthy hair follicle tissue of mice will be accompanied by persistent inflammation and tissue damage. In addition, excessive dead cell fragments will temporarily stimulate the proliferation of HFSCs, but this will also quickly deplete the cell pool of HFSCs. This forms a double blow to the healthy cycle of hair follicles.This may occur in some people with certain gene mutations (such as impaired RXRα).This can cause them to experience premature aging of hair follicles, hair loss or baldness.These findings may also help to better understand the working mechanism of hair follicles in the future and bring new strategies for treating hair loss.
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