March Week 1/2

1. A Scalable Suspension Platform for Generating High-Density Cultures of Universal Red Blood Cells from Human Induced Pluripotent Stem Cells (Sivalingam et al., 2020; Stem Cell Reports)

The goal of this paper is to describe a method to produce large quantities of stem cell-derived red blood cells (RBCs) for the purposes of transfusion medicine and also to solve the imminent global issue of a shortage of suitable donated blood. In particular, this group focuses on generating O-negative (O-neg) blood cells which makes sense since it is a universal donor blood type.

Previously, the group has already described a method to scale up the massive growth of pluripotent stem cells by culturing human induced pluripotent stem cells (iPSCs) on laminin-521 (LN-521)-coated microcarriers, which are small micro-sized beads with special surfaces to support cell attachment. So by using these microcarriers, they grew O-neg iPSCs and differentiated the cells into the hematopoietic mesoderm lineage under constant agitation (shaking). After the cells were directed to the hematopoietic mesoderm lineage, they were further expanded at the erythroblast expansion stage. Erythroblasts are precursors to erythrocytes/ RBCs. Using their method, they were able increase cell numbers to up to a 100-fold, producing up to 70 million cells in a 125ml spinner flask. In addition, they were able to use a 500ml spinner flask to produce about 100 million RBCs.

Next, they went on to compare the transcriptome profile of mass-produced RBCs to adult peripheral blood cells (blood cells isolated from crude blood). They showed that the mass-produced cells express genes involved in heme biosynthesis, erythropoiesis, cytoskeleton , similar to adult RBCs.Lastly, the authors confirmed that the mass-produced RBCs express alpha, beta and gamma globins while adult RBCs only express alpha and beta globins (adult hemoglobin) suggesting that the mass-produced RBCs may not be as mature as adult RBCs. To circumvent this, the adults showed that maturation of the stem cell-derived RBCs can be promoted by co-culturing mouse stromal cells. Mouse stromal cells were able to prompt higher rates of enucleation (erythroblast release their nucleus when maturing to erythrocytes) and reduced apoptosis (cell death). The authors also mentioned that enucleated RBCs could easily be enriched and purified by simply passing cells through non-woven fabric filters or leukocyte reduction filters.

In summary, the authors have developed an effective way of mass-producing stem cell-derived RBCs that closely resembles adult RBCs. They also introduced methods to increase maturity of the cells and to purify mature RBCs from less mature ones. The next steps will definitely be adapt this method to industrial-scale production and to determine if the RBCs will be transfusable in animal models.

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2. Structure and binding properties of Pangolin-CoV spike glycoprotein inform the evolution of SARS-CoV-2 (Wrobel et al., 2021; Nature Communications)

This interesting paper from a group at the Francis Crick Institute, U.K. looked to understand the evolutionary origin of the SARS-CoV-2 virus. There is obviously a lot of interest in understanding how this virus came to be.

There were several published-studies from last year suggesting that a type of virus called sarbecoviruses infecting Malayan pangolins resembles SARS-CoV-2, therefore, the authors hypothesized that the Malayan pangolins play a role in the emergence of the SARS-CoV-2 virus.

The authors first synthesized two Pangolin-CoV spike (S) proteins (based on known and published genetic sequences) and show that both proteins have strong affinity to human ACE2 (receptor of coronavirus S protein) but weaker binding to pangolin ACE2 and even weaker binding to bat ACE2. Also the binding affinity to human ACE2 is comparable to the binding affinity of SARS-CoV-2 to human ACE2 suggesting that the Pangolin-CoV can infect human cells very readily.

The authors also resolved the structure of the Pangolin-CoV S protein using cryo-EM and found that it is structurally similar to SARS-CoV-2 and that it adopts a fully-closed conformation (v.s. open conformation that is associated with facilitation of receptor binding). But all in all, they found that the sequence of the receptor-binding domain (ACE2 binding) of SARS-CoV-2 is similar to Pangolin-CoV but the non receptor-binding domain component of Pangolin-CoV such as the N-terminal domain is more similar to bat viruses. Therefore, the authors conclude that the existence of RBD of viruses that have high affinity to human ACE2, in the relevant zoonotic background, may account for the emergence of SARS-CoV-2, possible via a recombination of bat viruses.

3. Genome-wide association analyses of post-traumatic stress disorder and its symptom subdomains in the Million Veteran Program (Stein et al., 2021; Nature Genetics)

This paper looks at the genome-wide association analyses of PTSD amongst American verterans of European (EUR) and African (AFR) ancestry. In the EUR samples, they found three distinct genomic risk loci:

• Chr11:28707675, rs10767744, proximity mapped to METTL15

• Chr7:70219946, rs137999048, proximity mapped to AUTS2

• Chr7:1855531, rs7680, proximity mapped to MAD1L1

In the AFR samples, they identified two distinct risk loci:

• Chr3:1259951, rs4684090, intronic to CNTN6

• Chr20:6724577, rs112149412, near BMP2

They also found that some SNPs are associated with different phenotypes of PTSD such as re-experiencing, avoidance and hyperarousal and all symptoms (total). They also assessed the genetic correlations to other health-related traits and find strong positive associations with major depression, neuroticism and related symptoms but negative associations with education attainment and cognitive performance.

Lastly, the authors were able to implicate the cortical and subcortical regions of the brain and predict new drug targets for the treatment of PTSD.