Corrigendum: ACE2 knockout hinders SARS-CoV-2 propagation in iPS cell-derived airway and alveolar epithelial cells.

[This corrects the article DOI: 10.3389/fcell.2023.1290876.].

ACE2 knockout hinders SARS-CoV-2 propagation in iPS cell-derived airway and alveolar epithelial cells.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, continues to spread around the world with serious cases and deaths. It has also been suggested that different genetic variants in the human genome affect both the susceptibility to infection and severity of disease in COVID-19 patients. Angiotensin-converting enzyme 2 (ACE2) has been identified as a cell surface receptor for SARS-CoV and SARS-CoV-2 entry into cells. The construction of an experimental model system using human iPS cells would enable further studies of the association between viral characteristics and genetic variants. Airway and alveolar epithelial cells are cell types of the lung that express high levels of ACE2 and are suitable for in vitro infection experiments. Here, we show that human iPS cell-derived airway and alveolar epithelial cells are highly susceptible to viral infection of SARS-CoV-2. Using gene knockout with CRISPR-Cas9 in human iPS cells we demonstrate that ACE2 plays an essential role in the airway and alveolar epithelial cell entry of SARS-CoV-2 in vitro. Replication of SARS-CoV-2 was strongly suppressed in ACE2 knockout (KO) lung cells. Our model system based on human iPS cell-derived lung cells may be applied to understand the molecular biology regulating viral respiratory infection leading to potential therapeutic developments for COVID-19 and the prevention of future pandemics.

Restoration of Dystrophin Protein Expression by Exon Skipping Utilizing CRISPR-Cas9 in Myoblasts Derived from DMD Patient iPS Cells.

Duchenne muscular dystrophy (DMD) is a congenital X-linked disease caused by mutations in the gene encoding the dystrophin protein, which is required for myofiber integrity. Exon skipping therapy is an emerging strategy for restoring the open reading frame of the dystrophin gene to produce functional protein in DMD patients by skipping single or multiple exons. Although antisense oligonucleotides are able to target pre-mRNA for exon skipping, their half-lives are short and any therapeutic benefit is transient. In contrast, genome editing by DNA nucleases, such as the CRISPR-Cas9 system, could offer permanent correction by targeting genomic DNA. Our laboratory previously reported that disrupting the splicing acceptor site in exon 45 by plasmid delivery of the CRISPR-Cas9 system in iPS cells, derived from a DMD patient lacking exon 44, successfully restored dystrophin protein expression in differentiated myoblasts. Herein, we describe an optimized methodology to prepare myoblasts differentiated from iPS cells by mRNA transfection of the CRISPR-Cas9 system to skip exon 45 in myoblasts, and evaluate the restored dystrophin by RT-PCR and Western blotting.

Site-specific randomization of the endogenous genome by a regulatable CRISPR-Cas9 piggyBac system in human cells.

Randomized mutagenesis at an endogenous chromosomal locus is a promising approach for protein engineering, functional assessment of regulatory elements, and modeling genetic variations. In mammalian cells, however, it is challenging to perform site-specific single-nucleotide substitution with single-stranded oligodeoxynucleotide (ssODN) donor templates due to insufficient homologous recombination and the infeasibility of positive selection. Here, we developed a DNA transposon based CRISPR-Cas9 regulated transcription and nuclear shuttling (CRONUS) system that enables the stable transduction of CRISPR-Cas9/sgRNA in broad cell types, but avoids undesired genome cleavage in the absence two chemical inducing molecules. Highly efficient single nucleotide alterations induced randomization of desired codons (up to 4 codons) at a defined genomic locus in various human cell lines, including human iPS cells. Thus, CRONUS provides a novel platform for modeling diseases and genetic variations.

Differential expression of VGLUT1 or VGLUT2 in the trigeminothalamic or trigeminocerebellar projection neurons in the rat.

The vesicular glutamate transporters, VGLUT1 and VGLUT2, reportedly display complementary distribution in the rat brain. However, co-expression of them in single neurons has been reported in some brain areas. We previously found co-expression of VGLUT1 and VGLUT2 mRNAs in a number of single neurons in the principal sensory trigeminal nucleus (Vp) of the adult rat; the majority of these neurons sent their axons to the thalamic regions around the posteromedial ventral nucleus (VPM) and the posterior nuclei (Po). It is well known that trigeminothalamic (T-T) projection fibers arise not only from the Vp but also from the spinal trigeminal nucleus (Vsp), and that trigeminocerebellar (T-C) projection fibers take their origins from both of the Vp and Vsp. Thus, in the present study, we examined the expression of VGLUT1 and VGLUT2 in Vp and Vsp neurons that sent their axons to the VPM/Po regions or the cortical regions of the cerebellum. For this purpose, we combined fluorescence in situ hybridization (FISH) histochemistry with retrograde tract-tracing; immunofluorescence histochemistry was also combined with anterograde tract-tracing. The results indicate that glutamatergic Vsp neurons sending their axons to the cerebellar cortical regions mainly express VGLUT1, whereas glutamatergic Vsp neurons sending their axons to the thalamic regions express VGLUT2. The present data, in combination with those of our previous study, indicate that glutamatergic Vp neurons projecting to the cerebellar cortical regions express mainly VGLUT1, whereas the majority of glutamatergic Vp neurons projecting to the thalamus co-express VGLUT1 and VGLUT2.

Activation of the mammalian cells by using light-sensitive ion channels.

With advances in molecular biology and gene cloning techniques, it is now possible to selectively stimulate living cells of interest by using an external light source. This is done by transfecting the cells of interest with a plasmid carrying the channelrhodopsin (ChR2) gene. By stimulating these transfected cells with laser, the light-sensitive ion channels ChR2 are opened, followed by an influx of cation resulting in cell activation. This combination of optical and genetic technique is known in the literature as optogenetics. It is particularly useful in the functional studies of excitable cells, such as neurons, muscle and endocrine cells, to mimic the stimulation from action potentials to trigger the release neurotransmitters and hormones. Here, we describe the methods needed to make selected mammalian cells (PC12) respond to light excitation.