All this month we are using our blog and social media to highlight a new chapter in CIRM’s life, thanks to the voters approving Proposition 14. We are looking back at what we have done since we were created in 2004, and also looking forward to the future. Today we focus on groundbreaking CIRM funded research related to COVID-19 that was recently published.
It’s been almost a year since the world started hearing about SARS-CoV-2, the virus that causes COVID-19. In our minds, the pandemic has felt like an eternity, but scientists are still discovering new things about how the virus works and if genetics might play a role in the severity of the virus. One population study found that people who have ApoE4, a gene type that has been found to increase the risk of developing Alzheimer’s, had higher rates of severe COVID-19 and hospitalizations.
It is this interesting observation that led to important findings of a study funded by two CIRM awards ($7.4M grant and $250K grant) and conducted by Dr. Yanhong Shi at City of Hope and co-led by Dr. Vaithilingaraja Arumugaswami, a member of the UCLA Broad Stem Cell Research Center. The team found that the same gene that increases the risk for Alzheimer’s disease can increase the susceptibility and severity of COVID-19.
At the beginning of the study, the team was interested in the connection between SARS-CoV-2 and its effect on the brain. Due to the fact that patients typically lose their sense of taste and smell, the team theorized that there was an underlying neurological effect of the virus.
The team first created neurons and astrocytes. Neurons are cells that function as the basic working unit of the brain and astrocytes provide support to them. The neurons and astrocytes were generated from induced pluripotent stem cells (iPSCs), which are a kind of stem cell that can become virtually any type of cell and can be created by “reprogramming” the skin cells of patients. The newly created neurons and astrocytes were then infected with SARS-CoV-2 and it was found that they were susceptible to infection.
Next, the team used iPSCs to create brain organoids, which are 3D models that mimic certain features of the human brain. They were able to create two different organoid models: one that contained astrocytes and one without them. They infected both brain organoid types with the virus and discovered that those with astrocytes boosted SARS-CoV-2 infection in the brain model.
The team then decided to further study the effects of ApoE4 on susceptibility to SARS-CoV-2. They did this by generating neurons from iPSCs “reprogrammed” from the cells of an Alzheimer’s patient. Because the iPSCs were derived from an Alzheimer’s patient, they contained ApoE4. Using gene editing, the team modified some of the ApoE4 iPSCs created so that they contained ApoE3, which is a gene type considered neutral. The ApoE3 and ApoE4 iPSCs were then used to generate neurons and astrocytes.
The results were astounding. The ApoE4 neurons and astrocytes both showed a higher susceptibility to SARS-CoV-2 infection in comparison to the ApoE3 neurons and astrocytes. Moreover, while the virus caused damage to both ApoE3 and ApoE4 neurons, it appeared to have a slightly more severe effect on ApoE4 neurons and a much more severe effect on ApoE4 astrocytes compared to ApoE3 neurons and astrocytes.
“Our study provides a causal link between the Alzheimer’s disease risk factor ApoE4 and COVID-19 and explains why some (e.g. ApoE4 carriers) but not all COVID-19 patients exhibit neurological manifestations” says Dr. Shi. “Understanding how risk factors for neurodegenerative diseases impact COVID-19 susceptibility and severity will help us to better cope with COVID-19 and its potential long-term effects in different patient populations.”
In the last part of the study, the researchers tested to see if the antiviral drug remdesivir inhibits virus infection in neurons and astrocytes. They discovered that the drug was able to successfully reduce the viral level in astrocytes and prevent cell death. For neurons, it was able to rescue them from steadily losing their function and even dying.
The team says that the next steps to build on their findings is to continue studying the effects of the virus and better understand the role of ApoE4 in the brains of people who have COVID-19. Many people that developed COVID-19 have recovered, but long-term neurological effects such as severe headaches are still being seen months after.
“COVID-19 is a complex disease, and we are beginning to understand the risk factors involved in the manifestation of the severe form of the disease” says Dr. Arumugaswami. “Our cell-based study provides possible explanation to why individuals with Alzheimer’s’ disease are at increased risk of developing COVID-19.”
The full results to this study were published in Cell Stem Cell.