Bioengineering the hair follicle
Scientists believe they may have found a new way to reverse baldness
and treat conditions like premature balding and alopecia, which
is a partial or complete loss of hair that may result from radiation
therapy to the head, chemotherapy, skin disease or drug therapy.
Hair grows from follicles and new follicle cells are born from
stem cells that exist in a small bulge on the side of the hair
follicle. The innate ability of the hair follicle to regenerate
has led researchers and scientists to the conclusion that there
is a possibility of producing new hair follicles through tissue
engineering and stem cell technology.
Stem cells
No other area of scientific study has spawned as much intrigue,
excitement and controversy than stem cells. In-depth research
on stem cells has given humans advancing knowledge about how an
organism develops from a single cell and how healthy cells replace
damaged cells in adult organisms. This spectrum of futuristic
science is also showing scientists and researchers the path to
develop regenerative or reparative medicine or cell-based therapies
to treat diseases.
In their endeavor to seek answers to fundamental questions in
relation to long-term renewal of stem cells, scientists all over
the world are successfully growing these cells in the laboratory
and in turn using them for various tissue engineering and cellular
therapies including baldness.
So, what exactly are stem cells? Stem cells differ from other
kinds of cells in the body and irrespective of their source, have
three general properties: they are capable of dividing and renewing
themselves for long periods; they are unspecialized; and they
can choose to become one of the many different types of cells
present in the body based on signals from their environments.
Hair Follicle stem cells
Investigations and research by scientists in the field of stem
cell therapy have proven that creation of new hair follicles through
tissue engineering is possible. The investigators have identified
the critical molecules that act under genetic instruction to direct
the genes directly involved in hair follicle regeneration. In
research with mice, investigations revealed that tweaking of the
genes could produce furry mice or bald mice. This scientific breakthrough
has enabled the possibility of development of extra hair follicles
or impairment of the development of hair follicles in humans as
well.
How do hair follicles regenerate?
The hair follicle is a tiny organ with the inherent power of
being able to regenerate itself. At the base of the follicle is
the hair bulb, where wildly growing matrix cells become hair in
a series of intriguing steps. A little farther up the follicle
is the mysterious feature called the bulge, where the follicle
stem cells are ensconced. When stem cells receive the right set
of chemical signals, these self-renewing cells divide. One half
of the follicle stem cell splits into new cells that continue
to split and develop. The other half becomes a new stem cell,
and stays in place for future regeneration.
Hair Follicle Bioengineering Hurdles
The ideology behind bioengineering hair follicles is to harvest
healthy follicle stem cells. The challenge, however, lies not
in harvesting the cells, but in duplicating them. Unfortunately,
during the multiplication process the cells shed the genetic code
that directs them to turn into hair follicles.
Scientists have been working step by step towards cracking the
molecular orchestration code. Instead of transplanting them right
away, researchers have learned how to make the stem cells or seeds
multiply successfully by identifying the signaling molecules that
are responsible for development of epithelial buds, the precursor
to hair follicle formation. The new follicle stem cells that are
grown in laboratory cultures are attached then to tiny skin-cell
scaffolds and implanted into bald areas of the scalp.
The technical hurdle that scientists and researchers are confronted
with is defining the process of how these chemical signals act,
how they initiate the migration of stem cells and progenitor cells
to areas where they are required, and how these cells are ultimately
differentiated into the specialized cells of the layers of the
hair follicle.
The reason the solution has been so elusive is also the fact
that laboratory animal studies do not always translate into humans.
Most folliculoneogenesis studies have so far been successfully
conducted on animals, and only after a clinical study can scientists
say with conviction that bioengineering of the hair follicle is
achievable.
It has long been known that hair follicle development begins
in the very early embryo. In the fetus, there is an exchange of
molecular “signals” between the epidermal or outer
layer and underlying mesenchymal layers of cells that causes the
formation of a “bud” in the epidermal layer. The fact
that under normal circumstances, new hair follicles do not develop
in an adult makes the process of bioengineering new hair follicles
even more challenging.
Getting to the core of the matter
The overall goal is the indisputable revelation that cultured
human cells can induce new follicle formation and hair growth
in human skin. Ultimately the hope is that the research can be
used successfully to cure such conditions as premature balding
and alopecia and offer solutions for hair loss due to chemotherapy,
rather than from the cosmetic angle.
It is a well-established fact that adult hair follicles do not
grow and produce hair continuously but undergo intermittent phases
of regression before resuming a new growing phase. This entire
process is termed the follicle growth cycle. It is imperative
that the principal cell types in the follicle retain powerful
interactive signaling properties to maintain and control this
composite series of events. Scientists have been triumphant in
isolating dermal cells from the base of rodent follicles and shown
that small collections of these cells can induce new hair follicles
when combined with the epidermis.
There are two possible scenarios for using dermal inductive cells
to generate new follicles in bald scalps. Research has demonstrated
that the dermal cells from the base of the hair follicle, the
dermal papilla cells are the key to the formation of hair follicles
and to control hair growth in mature follicles. Dermal inductive
cells are a group of specialized cells at the base of the hair
follicle that give rise to the hair follicle at birth and supply
the materials necessary for hair growth during the life of the
person.
One approach to hair follicle cell based therapy would involve
removing a small number of hair follicles, isolating inductive
cells from them, and multiplying those cells while maintaining
their ability to regenerate new hair follicles. The other approach
actually entails forming hair follicles in vitro (biological phenomena
that are made to occur outside the living body), and then transplanting
the newly generated follicles back to the scalp.
In fact, Kurt S Stenn and Dr. George Cotsarelis have raised the
question that since the competence to form follicles is not exclusive
to bulge cells, there is a possibility that even other types of
stem cells could be coerced into forming hair follicles by proper
inductive cells.
Conclusion
No one can predict how soon dermatologists and pharmaceutical
companies will be able to make use of the discoveries emerging
from basic research into hair follicle development and cycling.
However, by working on cell types that “know” how
to form a hair follicle, researchers and scientists have made
remarkable progress and provided inspiration for future therapeutic
application.
Bioengineering the hair follicle references
- Stenn KS, Cotsarelis G.
Bioengineering the hair follicle: fringe benefits of stem cell
technology. Curr Opin Biotechnol. 2005 Oct;16(5):493-7. PMID:
16098737
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