So what did we learn?!
After Luka became stable from the acute liver failure, he did every test under the sun to try and understand what caused the liver to fail. The doctors were at a loss. We would have been in a diagnostic desert without Gene sequencing. So what did we learn?
THIS missense mutation causes degraded function in an assembly factor of the organellular proton pump, which enables a wide range of biological pathways. Ultimately, it results in defective protein synthesis, degradation, and the subsequent waste elimination.
PROTON PUMP
Proton pumps are an integral membrane protein located on the membranes in just about every cell of the body, but can have different roles depending on membrane location.
This particular protein is called a vacuolar ATPase, and are ATP-dependent proton pumps, found on the golgi and lysosome, whose functions include the acidification of intracellular compartments and the extrusion of protons through the cell cytoplasmic membrane. Lysosomes, endosomes, and a variety of other intracellular organelles are acidified by this assembly of unique proton pumps.
Proper pH environment within organelles is necessary for proper protein transport in support of a wide range of cellular processes.
WHAT DOES THAT MEAN?
Cellular acidity affects metabolism, protein synthesis, membrane transport, muscle function (as examples) through a variety of characterized biological pathways.
The Golgi apparatus, Lysosomes and Endoplasmic Reticulum maintain a specific organellular pH to create, modify, and degrade vital proteins.
Ok, so the pump is faulty, now what?
Life requires energy. The universal, biological fuel is a molecule called ATP, or Adenosine Triphosphate. This ATP6AP2 mutation belongs to a subset of V-ATPase defects linked to lysosomal storage disorders, congenital disorders of glycosylation, as well as neurological disorders.
Within this disease - there are multiple things happening at once that this pump is responsible for, that it can’t quite do properly.
Problem one: is during a process called glycosylation. Glycosylated proteins (glycoproteins) are proteins that have carbohydrate groups (or sugars) attached to each other to form a polypeptide chain that form in the golgi apparatus. These proteins travel through the golgi and endoplasmic reticulum as they carry out their protein synthesis.
In order for protein synthesis to take place, the process by which amino acids are linearly arranged into proteins through the involvement of ribosomal RNA, transfer RNA, messenger RNA, and various enzymes, the pH levels at the Golgi and Endoplasmic reticulum must be precisely maintained.
The last part of the process of glycosylation is adding a sialic acid component. (A fancy word for the last sugar on the sugar chain!) Sialyltransferases are enzymes that attach the sialic acids. With this disease, because the pH levels can’t quite be maintained, the sialyltransferases without the proper energy, get tired, or lazy, and can’t attached all the sugars on the chain.
Not fully glycosylated proteins can result in muscle weakness, low tone, potential muscle atrophy, a compromised immune system, and unhealthy brain function.
Problem One: Glycosylation
Problem Two: Protein Waste Removal
Autophagy is the body’s way of cleaning out old or damaged cells and regenerating new/healthier cells. A carrier structure called the autophagosome gathers up old waste and improperly made proteins by engulfing it like pac man, and takes it to the lysosome. It then fuses itself to the lysosome and pushes the junk into the lysosome to get degraded and recycled. A healthy lysosome regulates this process of autophagy in a feedback pathway loop, that breaks down waste into manageable components, providing building blocks for metabolism.
And how are these functions executed? You guessed it, they are reliant on a properly acidified environment, which is enabled by a functioning proton pump on the lysosomal membrane to generate the exact proton concentration within the lysosome.
Deficiencies in lysosomal pH disrupt autophagy and create a buildup of under-degraded waste. Within this disease, the buildup has created cirrhosis of the liver, brain developmental issues. It has also been linked to age-related diseases such as Parkinson’s, Alzheimer’s, Dementia, and Huntington’s disease.
The more junk that’s not able to be cleared, the more it will build up in the body and cause harm.
To achieve the ciritcal pH, lysosomes must have functional proton pumps to generate the exact proton concentration within the lysosome.
Glycosylation and synthesis at the Golgi, and lysosomal elimination and autophagy are critical pathways that are drastically impacted by mutations of the V-ATPase proteis.
OUR AIM:
To create a novel therapeutic that will address both glycosylation and autophagy issues.