In 2006, Professor Shinya Yamanaka's lab discovered that mature cells taken from an adult animal can be genetically reprogrammed into immature cells, also known as pluripotent stem cells. Pluripotent stem cells are embryonic cells, which can (as their name suggests) develop into any cell type in the adult body. Yamanaka was awarded the Nobel Prize in Physiology/Medicine
in 2012 for his work on reprogramming adult cells into pluripotent stem cells. In our lab, we make use of advancements made from this phenomenal discovery, to create human brain cells in two steps from minimally invasive skin biopsies, containing living cells donated to research.
We do this to study a heritable form of neurodegenerative disease, caused by a genetic mutation. All cells in our bodies harbour the same genetic code, so once we make brain cells, we can study the effect that any mutation has on brain cells. It is hugely beneficial to be able to study the effects of a genetic mutation on living human brain cells in a controlled microsystem in the lab. For us, the hope is to learn vital information about the complex disease process, so that we can design specific and safe therapies for people with this heritable disease. Some of the questions we try to answer are:
- Why are certain brain cells affected so specifically, when other cells in the body and brain are relatively spared, despite that they all harbour the same mutation?
- How come this particular mutation only causes major problems later in life when it is present from birth?
- Are brain cells made from different individual donors with the same mutation different with regard to their cellular disease markers?
- What mechanisms control the toxic effects of the mutation and how can we ameliorate or remove this toxicity?
This is how I spend a significant proportion of my time.
The brain cells like body temperature, so they live in in 37°C incubators. Though there is some harmless rust, the incubators are free of microorganisms. The cells are housed in clear plates where they adhere to the bottom and sit submerged in a pink-tinted nutrient solution. It has this colour because it contains a pH sensitive dye, which shows us the degree of cellular metabolism that has occurred since the solution was last replenished, as more metabolic byproducts = higher acidity in the solution.
Before we make brain cells, we need (induced) pluripotent stem cells, which have been re-engineered from human donor skin cells. Individuals with the mutation we study are asked in the neurology clinic if they consent to participating in research by donating a harmless biopsy of their skin. If they accept, some of their living skin cells are sent to the lab and made to express pluripotency genes, shaping them into pluripotent cells.
At this stage they need to be fed every day and closely monitored, as they divide quickly and dislike to be squeezed due to lack of space. We can grow more of them at this stage by lifting them from the plate and re-plating them in more plates, giving them more room to grow. They can also be frozen (cryopreserved) in liquid nitrogen at about -190°C for later resurrection and use. The process of making neurons (a type of brain cell) from the pluripotent cells takes about 3-4 weeks and mimics embryonic nervous system development, though it's more like a fast-forwarded shortcut.
At the end of this process, they're very young neurons, which still divide and need lots of care. For our experiments, we tend to make them exit this division cycle to mature them. Even the young, immature neurons self-organise into beautiful organic networks. The photo below is a light microscope image of mature neurons made by me. The small, dark and almost triangular puncta are their cell bodies, and the "branches" are their axons and dendrites, collectively known as neurites. It's through these that neurons connect and propagate electrical signals, called action potentials, which modulate the network electrochemically causing both short and long term changes. Neurons are inherently programmed to follow this morphological development, even when living in a lab dish without other supporting types of brain cells!