The Sunshine Vitamin, and its uses in IDDM

Vitamin D, or calcitriol in its active form, is an important vitamin for pancreatic actions because it is a prohormone. A prohormone enhances the effects of a primary hormone. Vitamin D enhances the primary hormone, pancreatic polypeptide, which is secreted by PP cells, or pancreatic progenitor cells. When this hormone is enhanced, beta cells are able secrete a large amount of insulin, which is a positive result for diabetic patients. However, if there is a lack of Vitamin D, then the pancreatic polypeptide hormone cannot be expressed as strongly, so insulin levels drop. We will now look at a deeper level to see how this works.

Molecules of calcitriol attach themselves to their specialized receptors, the Vitamin D Receptor, or VDR. VDR is a surface protein, or a protein that lies on the outside of a cell, that can only be generated if Vitamin D (image below) is present to bind to it. Let's see how VDR is actually made.

When a calcitriol molecule binds to VDR on the surface of a PP cell, a signal is sent to the nucleus of the cell to make copies of the section of DNA that codes (a.k.a exon- a segment of DNA that codes for a protein) for VDR. This copy of DNA, known as mRNA, then travels to the ribosome in small pieces. These pieces are called codons, and are brought over to the ribosome by tRNA, or "transfer RNA" and each one codes for an amino acid. Amino acids are the building blocks of proteins. There are 20 known common amino acids, which can be combined in different patterns and numbers to make the hundreds of thousands of proteins used by a cell. The ribosome is an organelle inside the cell that connects all of these amino acids from the codon to form a long string known as a protein. While it seems like a long process, cells can make thousands of proteins in an extremely short time.

Once VDR is created, like all proteins, it will travel to the golgi apparatus, which you can think of as a post office, because it sorts all the different proteins by their functions, and then ships them out to where they are supposed to go. The VDR protein is sent to the PP cell surface in order to allow the calcitriol to bind to it. Once this happens, a signal is sent back to the nucleus to make more VDR as well as to secrete more pancreatic polypeptide, which well be sent to the beta cell. Surface receptors on the beta cell will react with the pancreatic polypeptide and stimulate insulin production.

If Vitamin D levels drop, VDR cannot be created, and PP cells will not be able to make their polypeptide hormone, and insulin levels decrease. That is why Vitamin D is so important to beta cells, and this treatment is quickly being further researched, since it holds many possibilities for a cure.