Host metabolism dysregulation and cell tropism identification in human airway and alveolar organoids upon SARS-CoV-2 infection

The coronavirus disease 2019(COVID-19)pandemic is caused by infection with the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which is spread primary via respiratory droplets and infects the lungs.Currently widely used cell lines and animals are unable to accurately mimic human physiological conditions because of the abnormal status of cell lines(transformed or cancer cells)and species differences between animals and humans.Organoids are stem cell-derived selforganized three-dimensional culture in vitro and model the physiological conditions of natural organs.Here we showed that SARS-CoV-2 infected and extensively replicated in human embryonic stem cells(hESCs)-derived lung organoids,including airway and alveolar organoids which covered the complete infection and spread route for SARS-CoV-2 within lungs.The infected ceils were ciliated,club,and alveolar type 2(AT2)cells,which were sequentially located from the proximal to the distal airway and terminal alveoli,respectively.Additionally,RNA-seq revealed early cell response to virus infection including an unexpected downregulation of the metabolic processes,especially lipid metabolism,in addition to the well-known upregulation of immune response.Further,Remdesivir and a human neutralizing antibody potently inhibited SARS-CoV-2 replication in lung organoids.Therefore,human lung organoids can serve as a pathophysiological model to investigate the underlying mechanism of SARS-CoV-2 infection and to discover and test therapeutic drugs for COVID-19.

Single-cell analysis reveals bronchoalveolar epithelial dysfunction in COVID-19 patients

Dear Editor,In 2019,a zoonotic coronavirus named severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)was identified as the causative agent of Coronavirus Disease 2019(COVID-19).As of 8 June 2020,the World Health Organization(WHO)has reported 6,912,751 globally confirmed cases with 400,469 deaths.Although generally causes mild disease,SARS-CoV-2 infection can result in serious outcomes,including acute lung injury(ALI)and acute respiratory distress syndrome(ARDS),the leading cause of mortality in patients with comorbidities.Recent autopsy studies of COVID-19 patients revealed mononuclear infiltration and excessive production of mucus in the infected lung,especially in the damaged small airways and alveoli(Bian and Team,2020;Liu et al.,2020).

EMT and MET as paradigms for cell fate switching

Cell fate determination is a major unsolved problem in cell and developmental biology.The discovery of reprogramming by pluri-potent factors offers a rational system to investigate the molecular mechanisms associated with cell fate decisions.The idea that reprogramming of fibroblasts starts with a mesenchymal-epithelial transition(MET)suggests that the process is perhaps a reversal of epithelial to mesenchymal transition(EMT)found frequently during early embryogenesis.As such,we believe that investigations into MET-EMT may yield detailed molecular insights into cell fate decisions,not only for the switching between epithelial and mesenchymal cells,but also other cell types.

Global Profiling of the Lysine Crotonylome in Different Pluripotent States

Pluripotent stem cells(PSCs)can be expanded in vitro in different culture conditions,resulting in a spectrum of cell states with distinct properties.Understanding how PSCs transition from one state to another,ultimately leading to lineage-specific differentiation,is important for developmental biology and regenerative medicine.Although there is significant information regarding gene expression changes controlling these transitions,less is known about post-translational modifications of proteins.Protein crotonylation is a newly discovered post-translational modification where lysine residues are modified with a crotonyl group.Here,we employed affinity purification of crotonylated(LC–MS/MS)to systematically profile protein crotonylation in mouse PSCs in different states including ground,metastable,and primed states,as well as metastable PSCs undergoing early pluripotency exit.We successfully identified 3628 high-confidence crotonylated sites in 1426 proteins.These crotonylated proteins are enriched for factors involved in functions/processes related to pluripotency such as RNA biogenesis,central carbon metabolism,and proteasome function.Moreover,we found that increasing the cellular levels of crotonyl-coenzyme A(crotonyl-CoA)through crotonic acid treatment promotes proteasome activity in metastable PSCs and delays their differentiation,consistent with previous observations showing that enhanced proteasome activity helps to sustain pluripotency.Our atlas of protein crotonylation will be valuable for further studies of pluripotency regulation and may also provide insights into the role of metabolism in other cell fate transitions.

Reprogramming somatic cells to cells with neuronal characteristics by defined medium both in vitro and in vivo

Background:Currently,direct conversion from somatic cells to neurons requires virus-mediated delivery of at least one transcriptional factor or a combination of several small-molecule compounds.Delivery of transcriptional factors may affect genome stability,while small-molecule compounds may require more evaluations when applied in vivo.Thus,a defined medium with only conventional growth factors or additives for cell culture is desirable for inducing neuronal trans-differentiation.Results:Here,we report that a defined medium(5C)consisting of basic fibroblast growth factor(bFGF),N2 supplement,leukemia inhibitory factor,vitamin C(Vc),andβ-mercaptoethanol(βMe)induces the direct conversion of somatic cells to cells with neuronal characteristics.Application of 5C medium converted mouse embryonic fibroblasts(MEFs)into TuJ+neuronal-like cells,which were capable of survival after being transplanted into the mouse brain.The same 5C medium could convert primary rat astrocytes into neuronal-like cells with mature electrophysiology characteristics in vitro and facilitated the recovery of brain injury,possibly by inducing similar conversions,when infused into the mouse brain in vivo.Crucially,5C medium could also induce neuronal characteristics in several human cell types.Conclusions:In summary,this 5C medium not only provides a means to derive cells with neuronal characteristics without viral transfection in vitro but might also be useful to produce neurons in vivo for neurodegenerative disease treatment.

Generating a reporter mouse line marking medium spiny neurons in the developing striatum driven by Arpp21 cis-regulatory elements

The striatum, as the primary input nucleus in the basal ganglion,plays an important role in neural circuits crucial for the control of critical motivation, motor planning and procedural learning(Kreitzer and Malenka, 2008). Most cells in the striatum are GABAergic, including a large population (90%-95%) of medium spiny neurons (MSNs) and a small population of interneurons.