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subscription at Brilliant.org/SciShow. [♪ INTRO] So when you hear the word
“leprosy”, your brain may or may not conjure up an accurate
picture of Hansen’s disease: a bacterial infection that causes
skin lesions and nerve damage. Though you might correctly recall the enormous social stigma that persists
against people who are infected. Either way, your mind probably
doesn’t come up with any advantages. Like why would it? Well, according to some
scientists, studying the bacteria that cause Hansen’s disease could provide
incredible benefits to liver research… all thanks to one funky little mammal. Hansen’s disease is an infectious
disease caused by a bacterium called Mycobacterium leprae, or ML for short. In humans, these bacteria infect Schwann
cells, which are cells that protect the peripheral nervous system; that is, the
parts outside your brain and spinal cord. Schwann cells provide insulation
for the long axons of nerve cells. Some of them form the myelin
sheath, which helps to transmit electrical impulses that
carry messages between nerve cells. When nerve cells are damaged
from an injury or infection, Schwann cells receive signals to
revert to a relatively immature state. That reversion is called de-differentiation. As cells mature, they tend to split off into more specialized states; they differentiate. When that specialization gets put in
reverse, that’s de-differentiation. The cells become less mature and less specialized. Under typical circumstances, these
de-differentiated Schwann cells help axons regenerate, and that allows the peripheral nervous system to
recover from illness or injury. And at the end of the nerve repair process, the Schwann cells grow back up
into their differentiated states. And when a person contracts Hansen’s disease, the ML bacteria use this system to their benefit. ML bacteria reprogram Schwann
cells not just into an immature, de-differentiated state, but even further
into something resembling a stem cell. Stem cells can differentiate into
lots of different types of cells, but that’s sort of all that they do. A Schwann cell that’s de-differentiated this far isn’t good at being a Schwann cell any more. The de-differentiation process in
cells infected with ML bacteria causes damage to axons by
breaking down the myelin sheath. Cells without the physical barrier of
myelin are much easier for the bacteria to invade, so this helps the
bacteria evade the immune system. The result is chaos for those nerves
that needed that regenerative system. Without nerves that have the
ability to heal themselves, nerve damage in people with Hansen’s
disease can lead to loss of feeling or sensation, muscle weakness,
and sometimes even blindness. Strangely enough, however, there is a
scenario where ML infection has the nearly the opposite effect, promoting regeneration
in a very different kind of tissue. Liver tissue. The liver tissue… of nine-banded armadillos. ML infects not just humans,
but also some armadillos, native to North and South America. A 2022 study from researchers
at the University of Edinburgh has shown that nine-banded armadillos
infected with the ML bacteria grow bigger livers that are healthy
and functional in all respects. And it’s kind of similar to what the
bacteria are doing in human nerve cells: borrowing the host’s regenerative
processes for their own ends. In armadillos that carry ML bacteria, the
bacteria increase the expression of genes that code for proteins that are
typically associated with growth, wound-healing, and increased
metabolic responses in the liver. Even more fascinating, these are very
similar to genes and proteins that are expressed in human liver cells during
fetal development and adult growth. This de-differentiation that ML causes in
armadillo livers is temporary, allowing the cells to proliferate and then re-differentiate
into healthy specialized liver cells. This is less damaging than the
de-differentiation that ML causes in human nerve cells, where their
reversion to a stem-cell like state trashes their ability to heal themselves
since they cannot re-differentiate. Which shows how very similar
effects at the cellular level can lead to wildly different effects in
different tissues and different organisms. Now, tissue regeneration is an active
area of study for a couple of reasons. In humans, we want to keep
organs healthy as people age, and we want to understand
how to heal damaged tissue without cells growing out of
control and becoming cancerous. Scientists can revert mature cells to a
more stem cell-like state in rodent models. But… those cells tend to become cancerous. Which makes that method no
good for healing damaged organs in humans without some serious further study. Well, guess what armadillos infected
with ML bacteria DON’T have? They don’t have liver cancer! The researchers did not find any masses, tumors, or other tissue abnormalities in
any of the infected armadillos. And the ML bacteria’s little reprogramming act has little effect on genes that
encourage tumor growth. This reprogramming is likely
beneficial to the bacteria themselves, because by causing cell proliferation
and increased liver size, the bacteria get a nicer,
more nutrient-packed habitat. The bacteria also protect themselves
by keeping the host healthy, so it’s in their interest to not cause
any real harm to the host’s liver. And this isn’t just, like, ok, well
very lucky for armadillos I guess, because the researchers in the study
think this makes armadillos a great way to study how liver tissue regenerates
and apply that knowledge to humans. Liver disease causes millions of
deaths around the world every year. The human liver is typically
able to heal itself when needed. But that can be impaired in cases
like liver failure or cirrhosis. The researchers are hopeful that using
armadillos as a model of liver regeneration could help us develop tools to
heal damaged livers in humans, or maybe even grow brand new livers
to order when a transplant is needed. Which is a pretty unexpected upside
to one of the most hated diseases in human history interacting with
one of my favorite little animals. I’d like to think that it could
even help break down some stigma against people living with Hansen’s. Sometimes, nature creates silver
linings in the oddest of places. Researchers can find solutions in strange places when they look at problems from new angles. Sometimes it’s a matter of understanding
the variables you’re working with. Sometimes you need to work
backwards to find a solution. And those are all skills that you can learn from fundamental pre-algebra courses at Brilliant.org. Brilliant is an online learning platform with courses in science, computer science, and math. With Brilliant’s help, you
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Thanks for watching! [♪ OUTRO]
