Building a Disease Model

You need a map to know where you are, and where you’re going. That’s what Dr. Lewis has been charting for SIOD since 2017, discovering more detail about the disease pathway each year.

“We had to come up with models that we could create to further understand the disease—and quickly so that we could move toward developing new therapies for SIOD,” says Dr. Lewis.

To better study the mechanisms of SIOD and exactly how it affects the body, the Lewis Lab has pursued using induced pluripotent stem cells, or iPSCs, to model how the lack of SMARCAL1 protein in patients with SIOD leads to dysfunction of the immune system, the blood vessels supplying the brain, and the kidney cells involved in producing urine.

These experiments started with generating iPSCs from a blood sample from Jessica Davenport. As a carrier for SIOD, Jessica has one copy of the SMARCAL1 gene that encodes a normal protein and one copy of the gene that encodes the SMARCAL1 protein with a single amino acid change that eliminates the function of the protein.

Using a CRISPR genetic editing technique developed by the Stanford lab of Matthew Porteus, MD, PhD, her cells were converted to iPSCs in which both copies of the SMARCAL1 gene were normal or in which both copies had the same amino acid mutation. A portion of the corrected iPSCs were further modified so they could be safely eliminated with a harmless drug. Together, these models allowed the lab to study what happens when SMARCAL1 function is lost—either permanently or in a controlled, on-demand way—in iPSCs or in specialized cells made from them, including blood vessel lining cells (endothelial cells), immune cells, and kidney cells. Cells from these organs were selected because the lack of SMARCAL1 protein in SIOD patients harms their function. In addition, iPSCs generated from Paizlee were edited so that the copy of the SMARCAL1 gene she inherited from Jessica was corrected to have normal amino acid sequence. These create iPSCs that have only one abnormal copy of the SMARCAL1 gene and should have normal cell function similar to that of Jessica and Kyle and other heterozygous carriers of SIOD.

Studies using these cell lines have clearly shown that the missing SMARCAL1 protein leads to an accumulation of DNA damage at the ends of the chromosomes. These ends, which are called telomeres, are important in many cell types because they allow the cells to divide and maintain their normal function.

Now the Lewis Lab is trying to determine exactly how SMARCAL1 deficiency leads to telomere damage. Regardless of the precise mechanism, Dr. Lewis believes this telomere damage in endothelial cells is likely the reason why patients with SIOD develop serious neurological problems, including hemiplegic migraine headaches, temporary loss of blood flow to the brain, and strokes. The lab is using human umbilical vein endothelial cells—which are commercially available and come from the umbilical vein of the placenta after birth—and endothelial cells from the aorta tissue of adults who have undergone cardiac surgery to confirm that the same telomere damage occurs when both copies of SMARCAL1 are knocked out using another form of CRISPR gene editing.

The lab is also now seeking to grow endothelial colony-forming cells (ECFCs) directly from the blood of patients with SIOD. This is potentially a very important research approach, as it may validate the idea that endothelial cells from patients with SIOD have evidence of telomere damage in the endothelial cell precursors of the blood. Being able to isolate these cells may also lay the groundwork for genetically correcting them using CRISPR for infusion into the patients as therapy for the diseased blood vessels.

Dr. Lewis’ research is laying the groundwork for developing new therapies that may help limit severe headaches and reduce the risk of stroke in not only those with SIOD but anyone who is at risk for strokes, such as older individuals with atherosclerosis, or hardening of the arteries.

These studies also indicate how a mouse model of SIOD could be devised that might, for the first time, model the major features of SIOD in humans. With your support, the Lewis Lab is forging ahead with devising this mouse model to enable both drug discovery and testing in vivo for the blood vessel complications of SIOD. This model may be useful not only for SIOD, but also for evaluating other promising therapies to prevent strokes related to aging and atherosclerosis.