Cell fusion in the pathogenesis of COVID-19

Dear Editor,Infectionw ithsevereacuterespirator ysy ndrome coronavirus2(SARS-CoV-2),whichcausescoronavirus disease 2019 (COVID-19),is initiated by the virus spike (S)glycoprotein binding to its cellular receptor such as angiotensin converting enzyme 2 (ACE2)[1,2].Subsequently,the virus may take two routes for its entry into the host cells,including an endocytic route that ends up in endosomal compartment,and a plasma membrane route on the cell surface.In both routes,fusion between the viral and plasma membrane was required to introduce the viral genome into the cytoplasm[3].Similarly,SARS-CoV-2 infection results in the expression of fusogenic S glycoprotein on the host cell membrane.

Growth Inhibiton of Human Breast Cancer Cell Line MDA-MB-231 by Rosiglitazone through Activation of PPARγ

OBJECTIVE To investigate the anti-proliferative effect of rosiglitazone and its relationship to peroxisome proliferator-activated receptor γ （PPARγ） in human breast cancer cell line MDA-MB-231 and evaluate the potential application value of rosiglitazone for breast cancer therapy. METHODS The cytostatic effect of rosiglitazone on MDA- MB-231 cells was measured by the MTT assay. Cell-cycle kinetics was assessed by flow cytometry. Apoptotic cells were determined by the TUNEL assay. MDA-MB-231 cells were treated with rosiglitazone or in combination with the PPARy antagonist GW9662 to investigate the effect of rosiglitazone on cell proliferation and its relationship to PPARγ. RESULTS The results showed that rosiglitazone could inhibit growth of MDA-MB-231 cells in a dose- and time-dependent manner with an IC50 value of 5.2 μmol/L at 24 h after the drug was added into the culture. Cell cycle analysis showed that the percentage of G0/G1 phase cells increased, S phase cells decreased, and cells were arrested in G1 phase with increasing concentrations of rosiglitazone. Detectable signs of apoptotic cell death caused by rosiglitazone occurred at a concentration of 100 μmol/L and the apoptotic rate was （18 ± 3）%. PPARγ selective antagonist GW9662 could partially reverse the inhibitory effect of rosiglitazone on proliferation of MDA-MB-231 cells. CONCLUSION It was concluded that rosiglitazone can inhibit growth of MDA-MB-231 cells via PPARy activation and a high concentration of rosiglitazone can also induce MDA-MB-231 cell apoptosis. These results suggest that PPARy represents a putative molecular target for chemopreventive therapy and rosiglitazone may be effective in the treatment of breast cancer.

Survival, Proliferation and Cell Cycle of Swine Fibroblast after Infection with Salmonella enterica

Food-borne salmonellosis continues to be a major health concern worldwide. Carry-contamination of Salmonella frequently occurs in meat production. We focused on cell dynamics of swine fibroblasts after infection with Salmonella enterica serovar Enteritidis and Typhimurium, because fibroblast can be a target cell for Salmonella latent infection. It was found that both S. Enteritidis and S. Typhimurium were able to adhere and invade to swine fibroblasts. The proliferations in fibroblasts were different between each serovar. S. Enteritidis reached to the maximum at 24 hr after infection while S. Typhimurium did not. In addition, the decrease in the G0/G1 phase cells and increase in G2/M phase cells on the fibroblast were observed by both Salmonella infection. Cell death including apoptosis in the cells was inhibited by the infection of Salmonella. These results suggest that nontyphoidal Salmonella can survive for the long term by modifying bacterial cell proliferation and preventing cell death of host cells.

Fresh human amniotic membrane effectively promotes the repair of injured common peroneal nerve

Suture and autologous nerve transplantation are the primary therapeutic measures for completely severed nerves. However, imbalances in the microenvironment and adhesion of surrounding tissues can affect the quality of nerve regeneration and repair. Previous studies have shown that human amniotic membrane can promote the healing of a variety of tissues. In this study, the right common peroneal nerve underwent a 5-mm transection in rats. Epineural nerve repair was performed using 10/0 non-absorbable surgical suture. The repair site was wrapped with a two-layer amniotic membrane with α-cyanoacrylate rapid medical adhesive after suture. Hindlimb motor function was assessed using footprint analysis. Conduction velocity of the common peroneal nerve was calculated by neural electrical stimulation. The retrograde axoplasmic transport of the common peroneal nerve was observed using fast blue BB salt retrograde fluorescent staining. Hematoxylin- eosin staining was used to detect the pathological changes of the common peroneal nerve sputum. The mRNA expression of axon regeneration-related neurotrophic factors and inhibitors was measured using real-time polymerase chain reaction. The results showed that the amniotic membrane significantly improved the function of the injured nerve;the toe spread function rapidly recovered, the nerve conduction velocity was restored, and the number of fast blue BB salt particles were increased in the spinal cord. The amniotic membrane also increased the recovery rate of the tibialis anterior muscle and improved the tissue structure of the muscle. Meanwhile, mRNA expression of nerve growth factor, growth associated protein-43, collapsin response mediator protein-2, and brain-derived neurotrophic factor recovered to near-normal levels, while Lingo-1 mRNA expression decreased significantly in spinal cord tissues. mRNA expression of glial-derived neurotrophic factor did not change significantly. Changes in mRNA levels were more significant in amniotic-membrane-wrapping-treated rats compared with model and nerve sutured rats. These results demonstrate that fresh amniotic membrane wrapping can promote the functional recovery of sutured common peroneal nerve via regulation of expression levels of neurotrophic factors and inhibitors associated with axonal regeneration. The study was approved by the Committee on Animal Research and Ethics at the Affiliate Hospital of Zunyi Medical University, China (approval No. 112) on December 1, 2017.

Transfer of Lysozyme Gene into indica Parents of Hybrid Rice by Backcrossing

A lysozyme gene resistant to rice blast was transferred from the donor transgenic japonica rice Zhonghua 9 （D2-1-2） into a sterile line Pei＇ai 64S（PA 64S） and restorer line 9311 of the two-line hybrid rice Liangyoupeijiu, and the restorer line Minghui 63 （MH 63） of three-line hybrid rice Shanyou 63 by successive backcrossing. The PCR analysis confirmed that foreign lysozyme gene was segregated at ratio of 1 ： 1 in backcross generations of B39311, B3MH63 and B2PA64S, and at ratio of 3 ： 1 in selfed generations of B2F2 9311, B2F2 MH63 and B1F2 PA64S, indicating that the foreign gene was stably inherited over successive generations as a dominant single copy gene. The resistance against rice blast in backcross or selfed generations and corresponding testcross combinations were investigated in 2003 and 2004. The results showed that the resistance of the transgenic rice to blast had a greater improvement than that of the corresponding recurrent parents or the corresponding check hybrid combinations. The resistance of the advanced backcross and selfed generations to rice blast is much stronger than that of the early generations. The study confirmed that transferring the lysozyme gene into hybrid parents by backcrossing was a simple and effective approach to develop new hybrid rice resistant to rice blast.

Extracellular vesicles derived from mesenchymal stem cells:the wine in Hebe's hands to treat skin aging

Owing to its constant exposure to the external environment and various stimuli,skin ranks among the organs most vulnerable to manifestations of aging.Preventing and delaying skin aging has become one of the prominent research subjects in recent years.Mesenchymal stem celis(MsCs)are multipotent stem cells derived from mesoderm with high self-renewal ability and multilineage differentiation potential.MSC-derived extracellular vesicles(MSC-EVs)are nanoscale biological vesicles that facilitate intercellular communication and regulate biological behavior.Recent studies have shown that MSC-EVs have potential applications in anti-aging therapy due to their anti-inflammatory,anti-oxidative stress,and wound healing promoting abilities.This review presents the latest progress of MSC-EVs in delaying skin aging.It mainly includes the MSC-EVs promoting the proliferation and migration of keratinocytes and fibroblasts,reducing the expression of matrix metalloproteinases,resisting oxidative stress,and regulating inflammation.We then briefly discuss the recently discovered treatment methods of MSc-EVs in the field of skin anti-aging.Moreover,the advantages and limitations of EV-based treatments are also presented.

Hematopoietic aging:Cellular,molecular,and related mechanisms

Aging is accompanied by significant inhibition of hematopoietic and immune system function and disruption of bone marrow structure.Aging-related alterations in the inflammatory response,immunity,and stem cell niches are at the root of hematopoietic aging.Understanding the molecular mechanisms underlying hematopoietic and bone marrow aging can aid the clinical treatment of aging-related diseases.In particular,it is unknown how the niche reprograms hematopoietic stem cells(HSCs)in an age-dependent manner to maintain normal hematopoiesis in elderly individuals.Recently,specific inhibitors and blood exchange methods have been shown to reshape the hematopoietic niche and reverse hematopoietic aging.Here,we present the latest scientific discoveries related to hematopoietic aging and hematopoietic system rejuvenation,discuss the relationships between hematopoietic niche aging and HSC aging,and describe related studies on stem cell-mediated regulation of hematopoietic aging,aiming to provide new ideas for further study.

A human-specific insertion promotes cell proliferation and migration by enhancing TBC1D8B expression

Human-specific insertions play important roles in human phenotypes and diseases.Here we reported a 446-bp insertion(Insert-446)in intron 11 of the TBC1D8B gene,located on chromosome X,and traced its origin to a portion of intron 6 of the EBF1 gene on chromosome 5.Interestingly,Insert-446 was present in the human Neanderthal and Denisovans genomes,and was fixed in humans after human-chimpanzee divergence.We have demonstrated that Insert-446 acts as an enhancer through binding transcript factors that promotes a higher expression of human TBC1D8B gene as compared with orthologs in macaques.In addition,over-expression TBC1D8B promoted cell proliferation and migration through“a dual finger”catalytic mechanism(Arg538 and Gln573)in the TBC domain in vitro and knockdown of TBC1D8B attenuated tumorigenesis in vivo.Knockout of Insert-446 prevented cell proliferation and migration in cancer and normal cells.Our results reveal that the human-specific Insert-446 promotes cell proliferation and migration by upregulating the expression of TBC1D8B gene.These findings provide a significant insight into the effects of human-specific insertions on evolution.

Biomimetic cell-adhesive ligand-functionalized peptide composite hydrogels maintain stemness of human amniotic mesenchymal stem cells

In vivo,stem cells reside in a three-dimensional(3D)extracellular microenvironment in which complicated biophysical and biochemical factors regulate their behaviors.Biomimicking of the stem cellmatrix interactions is an ideal approach for controlling the stem cell fate.This study investigates the effects of the incorporation of cell-adhesive ligands in 3D self-assembling peptide hydrogels to modulate stem cell survival,proliferation,maintenance of stemness,and osteogenic differentiation.The results show that the composite hydrogels were non-cytotoxic and effective for maintaining human amniotic mesenchymal stem cell(hAMSC)survival,proliferation and phenotypic characterization.The expression levels of pluripotent markers were also upregulated in the composite hydrogels.Under inductive media conditions,mineral deposition and mRNA expression levels of osteogenic genes of hAMSCs were enhanced.The increasing expression of integrin aand b-subunits for hAMSCs indicates that the ligandintegrin interactions may modulate the cell fate for hAMSCs in composite hydrogels.

Identification and validation of heterotypic cell-in-cell structure as an adverse prognostic predictor for young patients of resectable pancreatic ductal adenocarcinoma

Dear Editor,Pancreatic ductal adenocarcinoma(PDAC)has a poor prognosis,with an overall 5-year survival rate of less than 10%.Between 20 and 30%of PDAC cases are resectable at diagnosis;however,patients’post-operative survival periods vary widely,irrespective of active therapeutic interventions.1 Therefore,extensive efforts have been made to identify biomarkers that may identify patients with an improved prognosis.Although profound local immune suppression had been implicated in PDAC progression and poor patient survival,a prognostic marker that can directly and functionally read immune evasion in situ is not yet available.

N501Y mutation imparts cross-species transmission of SARS-CoV-2 to mice by enhancing receptor binding

Dear Editor,According to the World Health Organization(WHO),as of March 8,2021,the pandemic caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)had infected more than 116 million patients with coronavirus disease 2019(COVID-19)(https://covid19.who.int).The high infectivity of SARS-CoV-2 is largely attributable to the unique sequence composition of its spike(S)glycoprotein.

The virological impacts of SARS-CoV-2 D614G mutation

The coronavirus diseases 2019(COVID-19)caused by the infection of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)emerged in December 2019 has caused more than 140 million infections worldwide by the end of April 2021.As an enveloped single-stranded positive-sense RNA virus,SARS-CoV-2 underwent constant evolution that produced novel variants carrying mutation conferring fitness advantages.The current prevalent D614G variant,with glycine substituted for aspartic acid at position 614 in the spike glycoprotein,is one of such variants that became the main circulating strain worldwide in a short period of time.Over the past year,intensive studies from all over the world had defined the epidemiological characteristics of this highly contagious variant and revealed the underlying mechanisms.This review aims at presenting an overall picture of the impacts of D614G mutation on virus transmission,elucidating the underlying mechanisms of D614G in virus pathogenicity,and providing insights into the development of effective therapeutics.

Molecular mechanisms underlying cell-in-cell formation:core machineries and beyond

Although cell-in-cell structures(CICs),with one or more cells present inside another cell,had been identified for a century,it was not until recent years that scientists started to uncover their pivotal roles in multiple biological processes,primarily via mediating the death of internalized cells.Meanwhile,considerable progresses were made on deciphering the mechanisms underlying their formation based on different models.Entosis was one of the best investigated CIC models,where cell internalization was coordinately driven by adherens junction and contractile ac-tomyosin,the two spatially polarized and complementary core elements that were coupled by mechanical ring,a recently identified core element.Meanwhile,an expanding group of factors were found capable of regulating CIC formation by targeting these core elements.The elucidation of the molecular machinery controlling CIC formation enables synthetic engineering of cells used for clinical and research purposes。

Chemical approach to generating long-term self-renewing pMN progenitors from human embryonic stem cells

Spinal cord impairment involving motor neuron degeneration and demyelination can cause lifelong disabilities,but effective clinical interventions for restoring neurological functions have yet to be developed.In early spinal cord development,neural progenitors of the motor neuron(pMN)domain,defined by the expression of oligodendrocyte transcription factor 2(OLIG2),in the ventral spinal cord first generate motor neurons and then switch the fate to produce myelin-forming oligodendrocytes.Given their differentiation potential,pMN progenitors could be a valuable cell source for cell therapy in relevant neurological conditions such as spinal cord injury.However,fast generation and expansion of pMN progenitors in vitro while conserving their differentiation potential has so far been technically challenging.In this study,based on chemical screening,we have developed a new recipe for efficient induction of pMN progenitors from human embryonic stem cells.More importantly,these OLIG2+pMN progenitors can be stably maintained for multiple passages without losing their ability to produce spinal motor neurons and oligodendrocytes rapidly.Our results suggest that these self-renewing pMN progenitors could potentially be useful as a renewable source of cell transplants for spinal cord injury and demyelinating disorders.

AIM-CICs: an automatic identification method for cell-in-cell structures based on convolutional neural network

Whereas biochemical markers are available for most types of cell death, current studies on non-autonomous cell death by entosis rely strictly on the identification of cell-in-cell structures (CICs), a unique morphological readout that can only be quantified manually at present. Moreover, the manual CIC quantification is generally over-simplified as CIC counts, which represents a major hurdle against profound mechanistic investigations. In this study, we take advantage of artificial intelligence technology to develop an automatic identification method for CICs (AIM-CICs), which performs comprehensive CIC analysis in an automated and efficient way. The AIM-CICs, developed on the algorithm of convolutional neural network, can not only differentiate between CICs and non-CICs (the area under the receiver operating characteristic curve (AUC) > 0.99), but also accurately categorize CICs into five subclasses based on CIC stages and cell number involved (AUC > 0.97 for all subclasses). The application of AIM-CICs would systemically fuel research on CIC-mediated cell death, such as high-throughput screening.

Structure basis for the unique specificity of medaka enteropeptidase light chain

Dear Editor, Enteropeptidase （enterokinase, EC 3.4.21.9） is a serine protease, which shows a specific cleavage of its substrates at the C-terminal of the recognition site （Asp）4Lys （Zheng et al., 2009）. Because of the unique specificity, enteropep- tidase could be used as a tool for the production of recom- binant fusion proteins. Especially the recombinant enteropeptidase light chain （EPL）, which contains a catalytic domain, is of large interest to be applied in biopharmaceu- tical industry （Lu et al., 1997）.