The hair-raising reason for goosebumps
The same cell types that cause goosebumps are responsible for controlling
hair growth

Date:
July 20, 2020
Source:
Harvard University
Summary:
Researchers have discovered that the cells that cause goosebumps
are also important for regulating the stem cells that regenerate
hair. In the skin, the muscle that contracts to create goosebumps
is necessary to bridge the sympathetic nerve's connection to hair
follicle stem cells.

The sympathetic nerve reacts to cold by contracting the muscle
and causing goosebumps in the short term, and by driving stem cell
activation and new hair growth over the long term.



FULL STORY ==========================================================================
If you've ever wondered why we get goosebumps, you're in good company
-- so did Charles Darwin, who mused about them in his writings on
evolution. Goosebumps might protect animals with thick fur from the
cold, but we humans don't seem to benefit from the reaction much --
so why has it been preserved during evolution all this time?

==========================================================================
In a new study, Harvard University scientists have discovered the reason:
the cell types that cause goosebumps are also important for regulating
the stem cells that regenerate the hair follicle and hair. Underneath
the skin, the muscle that contracts to create goosebumps is necessary
to bridge the sympathetic nerve's connection to hair follicle stem
cells. The sympathetic nerve reacts to cold by contracting the muscle
and causing goosebumps in the short term, and by driving hair follicle
stem cell activation and new hair growth over the long term.

Published in the journal Cell, these findings in mice give researchers
a better understanding of how different cell types interact to link stem
cell activity with changes in the outside environment.

"We have always been interested in understanding how stem cell behaviors
are regulated by external stimuli. The skin is a fascinating system: it
has multiple stem cells surrounded by diverse cell types, and is located
at the interface between our body and the outside world. Therefore,
its stem cells could potentially respond to a diverse array of stimuli
-- from the niche, the whole body, or even the outside environment,"
said Ya-Chieh Hsu, the Alvin and Esta Star Associate Professor of Stem
Cell and Regenerative Biology, who led the study in collaboration with Professor Sung-Jan Lin of National Taiwan University. "In this study, we identify an interesting dual-component niche that not only regulates the
stem cells under steady state, but also modulates stem cell behaviors
according to temperature changes outside." A system for regulating
hair growth Many organs are made of three types of tissue: epithelium, mesenchyme, and nerve. In the skin, these three lineages are organized
in a special arrangement. The sympathetic nerve, part of our nervous
system that controls body homeostasis and our responses to external
stimuli, connects with a tiny smooth muscle in the mesenchyme. This
smooth muscle in turn connects to hair follicle stem cells, a type of epithelial stem cell critical for regenerating the hair follicle as well
as repairing wounds.



==========================================================================
The connection between the sympathetic nerve and the muscle has been
well known, since they are the cellular basis behind goosebumps: the
cold triggers sympathetic neurons to send a nerve signal, and the muscle
reacts by contracting and causing the hair to stand on end. However,
when examining the skin under extremely high resolution using electron microscopy, the researchers found that the sympathetic nerve not only associated with the muscle, but also formed a direct connection to the
hair follicle stem cells. In fact, the nerve fibers wrapped around the
hair follicle stem cells like a ribbon.

"We could really see at an ultrastructure level how the nerve and the
stem cell interact. Neurons tend to regulate excitable cells, like other neurons or muscle with synapses. But we were surprised to find that
they form similar synapse-like structures with an epithelial stem cell,
which is not a very typical target for neurons," Hsu said.

Next, the researchers confirmed that the nerve indeed targeted the
stem cells.

The sympathetic nervous system is normally activated at a constant low
level to maintain body homeostasis, and the researchers found that this
low level of nerve activity maintained the stem cells in a poised state
ready for regeneration. Under prolonged cold, the nerve was activated at
a much higher level and more neurotransmitters were released, causing
the stem cells to activate quickly, regenerate the hair follicle, and
grow new hair.

The researchers also investigated what maintained the nerve connections
to the hair follicle stem cells. When they removed the muscle connected
to the hair follicle, the sympathetic nerve retracted and the nerve
connection to the hair follicle stem cells was lost, showing that the
muscle was a necessary structural support to bridge the sympathetic
nerve to the hair follicle.

How the system develops In addition to studying the hair follicle in
its fully formed state, the researchers investigated how the system
initially develops -- how the muscle and nerve reach the hair follicle
in the first place.



==========================================================================
"We discovered that the signal comes from the developing hair follicle
itself.

It secretes a protein that regulates the formation of the smooth
muscle, which then attracts the sympathetic nerve. Then in the adult,
the interaction turns around, with the nerve and muscle together
regulating the hair follicle stem cells to regenerate the new hair
follicle. It's closing the whole circle -- the developing hair follicle
is establishing its own niche," said Yulia Shwartz, a postdoctoral fellow
in the Hsu lab. She was a co-first author of the study, along with Meryem Gonzalez-Celeiro, a graduate student in the Hsu Lab, and Chih-Lung Chen,
a postdoctoral fellow in the Lin lab.

Responding to the environment With these experiments, the researchers identified a two-component system that regulates hair follicle stem
cells. The nerve is the signaling component that activates the stem
cells through neurotransmitters, while the muscle is the structural
component that allows the nerve fibers to directly connect with hair
follicle stem cells.

"You can regulate hair follicle stem cells in so many different
ways, and they are wonderful models to study tissue regeneration,"
Shwartz said. "This particular reaction is helpful for coupling tissue regeneration with changes in the outside world, such as temperature. It's
a two-layer response: goosebumps are a quick way to provide some sort of
relief in the short term. But when the cold lasts, this becomes a nice mechanism for the stem cells to know it's maybe time to regenerate new
hair coat." In the future, the researchers will further explore how
the external environment might influence the stem cells in the skin,
both under homeostasis and in repair situations such as wound healing.

"We live in a constantly changing environment. Since the skin is always
in contact with the outside world, it gives us a chance to study what mechanisms stem cells in our body use to integrate tissue production
with changing demands, which is essential for organisms to thrive in
this dynamic world," Hsu said.


========================================================================== Story Source: Materials provided by Harvard_University. Original written
by Jessica Lau.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yulia Shwartz, Meryem Gonzalez-Celeiro, Chih-Lung Chen, H. Amalia
Pasolli, Shu-Hsien Sheu, Sabrina Mai-Yi Fan, Farnaz Shamsi, Steven
Assaad, Edrick Tai-Yu Lin, Bing Zhang, Pai-Chi Tsai, Megan He,
Yu-Hua Tseng, Sung-Jan Lin, Ya-Chieh Hsu. Cell Types Promoting
Goosebumps Form a Niche to Regulate Hair Follicle Stem Cells. Cell,
2020; DOI: 10.1016/ j.cell.2020.06.031 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200720112325.htm

--- up 5 days, 1 hour, 54 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)