Biomedical subjects

Mei Chen

Publications and source records attributed to Mei Chen.

At least 19 recordsLinked to original sources

PubMed2026

MDV-like endogenous viral elements act as immune rheostats in Aedes cells by modulating defensin A-mediated responses to arboviruses.

Mosquito cell lines are essential tools for arbovirus research. Endogenous viral elements (EVEs) are prevalent in mosquito genomes, yet their functional effects on host immune responses remain unclear, potentially complicating experimental interpretations. In this study, we systematically characterized endogenous mosquito densovirus-like elements (EMLs) within the Aedes aegypti Aag2 cell line and found that these endogenous EMLs are transcriptionally active but translationally defective. The silencing of EML transcripts significantly diminished the replication of Zika virus (ZIKV), Japanese encephalitis virus (JEV), and chikungunya virus (CHIKV), while transiently increasing dengue virus 2 (DENV-2), thereby indicating a virus-dependent regulatory mechanism. Mechanistically, RNA sequencing after EML interference, alongside plasmid-based mimic expression, demonstrated that EML transcripts downregulate defensin A, an antimicrobial peptide produced by mosquitoes. Functional assays using synthetic defensin A showed that this peptide differentially regulates arboviral infection. Binding assays and structural modeling further supported its interaction with viral envelope proteins, while stage-restricted infection assays revealed distinct stages of action: defensin A enhanced adsorption of ZIKV, JEV, and CHIKV, but did not promote DENV-2 adsorption or entry, and instead reduced DENV-2 RNA accumulation at the post-entry replication stage. Our findings highlight a previously unrecognized role of densovirus-derived EVEs in mosquito innate immunity, extending their functional scope from the well-established PIWI-interacting RNA-mediated antiviral defense to the regulation of antimicrobial peptide-associated immune pathways. These findings emphasize the necessity of accounting for EVE activity when analyzing data derived from mosquito cell lines, and suggest that related EVE-mediated immune regulation may contribute to arbovirus dynamics in mosquitoes.IMPORTANCEMosquito-borne viruses such as dengue, Zika, Japanese encephalitis, and chikungunya continue to threaten human health worldwide. Laboratory studies often use Aedes aegypti cell lines to investigate how these viruses interact with their mosquito hosts. Here, we show that the genomes of these cells contain endogenous viral elements derived from mosquito densoviruses. Far from being inert fossils, these sequences are transcriptionally active and regulate mosquito immunity by suppressing the antimicrobial peptide defensin A. This immune modulation influences the replication of different arboviruses in opposite ways, enhancing some while restricting others. Our findings reveal that integrated viral elements can shape the outcome of arbovirus infection, with important implications for interpreting mosquito cell culture experiments and for evaluating endogenous viral element-mediated immune regulation in mosquito-virus interactions.

Aag2 cell↗

PubMed2025

A method for the detection and enrichment of endogenous cereblon substrates.

C-terminal cyclic imides are posttranslational modifications (PTMs) on proteins that are recognized and removed by the E3 ligase substrate adapter cereblon (CRBN). Despite the observation of these modifications across the proteome by mass spectrometry-based proteomics, an orthogonal and generalizable method to visualize the C-terminal cyclic imide would enhance detection, sensitivity, and throughput of endogenous CRBN substrate characterization. Here, we develop an antibody-like reagent, termed "cerebody," for visualizing and enriching C-terminal cyclic imide-modified proteins. We describe the engineering of CRBN derivatives to produce cerebody and use it to identify CRBN substrates by western blot and enrichment from whole-cell and tissue lysates. CRBN substrates identified by cerebody enrichment are mapped, validated, and further characterized for dependence on the C-terminal cyclic imide modification. These methods will accelerate the characterization of endogenous CRBN substrates and their regulation.

Humans↗

PubMed2007

Study of performance of a He-Ne laser having an annular gain zone.

A He-Ne laser with an annular gain zone is studied theoretically. It is demonstrated that the He-Ne medium in the annular discharge zone possesses enough gain to maintain laser oscillation. A multipass ring resonator, which is composed of two annular spherical mirrors, is described, and it is shown that the resonator is suitable for extracting optical energy from the He-Ne medium in the annular gain zone. Considering the availability of population inversion in the traveling-wave cavity and the influence of the crossover of the folded light beam in the resonator on the output power, a calculation formula for the output power of the laser with the multipass ring resonator is given. Calculating results prove that a 1 W output of the He-Ne laser can be obtained by a 1 m length annular discharge zone.

Journal Article↗

PubMed2006

Characterization of the protective T-cell response generated in CD4-deficient mice by a live attenuated Mycobacterium tuberculosis vaccine.

The global epidemic of tuberculosis, fuelled by acquired immune-deficiency syndrome, necessitates the development of a safe and effective vaccine. We have constructed a DeltaRD1DeltapanCD mutant of Mycobacterium tuberculosis (mc(2)6030) that undergoes limited replication and is severely attenuated in immunocompromised mice, yet induces significant protection against tuberculosis in wild-type mice and even in mice that completely lack CD4(+) T cells as a result of targeted disruption of their CD4 genes (CD4(-/-) mice). Ex vivo studies of T cells from mc(2)6030-immunized mice showed that these immune cells responded to protein antigens of M. tuberculosis in a major histocompatibility complex (MHC) class II-restricted manner. Antibody depletion experiments showed that antituberculosis protective responses in the lung were not diminished by removal of CD8(+), T-cell receptor gammadelta (TCR-gammadelta(+)) and NK1.1(+) T cells from vaccinated CD4(-/-) mice before challenge, implying that the observed recall and immune effector functions resulting from vaccination of CD4(-/-) mice with mc(2)6030 were attributable to a population of CD4(-) CD8(-) (double-negative) TCR-alphabeta(+), TCR-gammadelta(-), NK1.1(-) T cells. Transfer of highly enriched double-negative TCR-alphabeta(+) T cells from mc(2)6030-immunized CD4(-/-) mice into naive CD4(-/-) mice resulted in significant protection against an aerosol tuberculosis challenge. Enriched pulmonary double-negative T cells transcribed significantly more interferon-gamma and interleukin-2 mRNA than double-negative T cells from naive mice after a tuberculous challenge. These results confirmed previous findings on the potential for a subset of MHC class II-restricted T cells to develop and function without expression of CD4 and suggest novel vaccination strategies to assist in the control of tuberculosis in human immunodeficiency virus-infected humans who have chronic depletion of their CD4(+) T cells.

Adoptive Transfer↗

PubMed2006

Neuroprotection by endogenous and exogenous PACAP following stroke.

We investigated the effects of PACAP treatment, and endogenous PACAP deficiency, on infarct volume, neurological function, and the cerebrocortical transcriptional response in a mouse model of stroke, middle cerebral artery occlusion (MCAO). PACAP-38 administered i.v. or i.c.v. 1 h after MCAO significantly reduced infarct volume, and ameliorated functional motor deficits measured 24 h later in wild-type mice. Infarct volumes and neurological deficits (walking faults) were both greater in PACAP-deficient than in wild-type mice, but treatment with PACAP reduced lesion volume and neurological deficits in PACAP-deficient mice to the same level of improvement as in wild-type mice. A 35,546-clone mouse cDNA microarray was used to investigate cortical transcriptional changes associated with cerebral ischemia in wild-type and PACAP-deficient mice, and with PACAP treatment after MCAO in wild-type mice. 229 known (named) transcripts were increased (228) or decreased (1) in abundance at least 50% following cerebral ischemia in wild-type mice. 49 transcripts were significantly up-regulated only at 1 h post-MCAO (acute response transcripts), 142 were up-regulated only at 24 h post-MCAO (delayed response transcripts) and 37 transcripts were up-regulated at both times (sustained response transcripts). More than half of these are transcripts not previously reported to be altered in ischemia. A larger percentage of genes up-regulated at 24 hr than at 1 hr required endogenous PACAP, suggesting a more prominent role for PACAP in later response to injury than in the initial response. This is consistent with a neuroprotective role for PACAP in late response to injury, i.e., even when administered 1 hr or more after MCAO. Putative injury effector transcripts regulated by PACAP include beta-actin, midline 2, and metallothionein 1. Potential neuroprotective transcripts include several demonstrated to be PACAP-regulated in other contexts. Prominent among these were transcripts encoding the PACAP-regulated gene Ier3, and the neuropeptides enkephalin, substance P (tachykinin 1), and neurotensin.

Animals↗

PubMed2006

Mycobacterium tuberculosis DeltaRD1 DeltapanCD: a safe and limited replicating mutant strain that protects immunocompetent and immunocompromised mice against experimental tuberculosis.

The global epidemic of tuberculosis (TB), fueled by the growing HIV pandemic, warrants the development of a safe and effective vaccine against TB. We report the construction and characterization of an unlinked double deletion mutant of Mycobacterium tuberculosis H37Rv that deletes both the primary attenuating mutation of BCG (DeltaRD1) and two genes required for the synthesis of pantothenate (DeltapanCD). The M. tuberculosis DeltaRD1 DeltapanCD (mc(2)6030) mutant undergoes limited replication in mice, and yet is both significantly safer than BCG in immunocompromised mice and also safe in guinea pigs. Additionally, the mc(2)6030 strain does not reactivate in a mouse chemo-immunosuppression model. Importantly, long-lived protective immune responses following immunization with the mc(2)6030 strain prolong the survival of wild type mice, and CD4-deficient mice against an aerosol challenge with virulent M. tuberculosis. Given its overall safety and effectiveness, the mc(2)6030 live attenuated strain should be considered as a human vaccine candidate for protecting both healthy and HIV-infected individuals against TB.

Animals↗

PubMed2006

Transforming growth factor-alpha: a major human serum factor that promotes human keratinocyte migration.

In unwounded skin, human keratinocytes (HKs) are in contact with a plasma filtrate. In an acute wound, HKs come in contact with serum for the first time. Because human serum (HS), but not plasma, promotes HK migration, we speculated that a major HK pro-motility factor in vivo comes from serum. In this study, we compared all of the published growth factors (GFs), reported to promote HK migration, with HS. No single GF could duplicate the HK pro-motility activity in HS. Among these GFs, transforming growth factor-alpha [corrected] showed the highest HK pro-motility activity, reaching approximately 80% of the activity in HS. The order of potency was: TGFalpha > insulin > EGF > heparin binding (HB)-EGF > IGF-1 > basic fibroblast growth factor >IL-8 > HGF > IL-1 > KGF>TGFbeta. Interestingly, the combination of TGFalpha and insulin could duplicate the HK pro-motility activity in HS, although only the TGFalpha, but not insulin, levels increase in serum over plasma. Addition of neutralizing antibodies against TGFalpha to serum or depletion of TGFalpha from serum by immunoprecipitation significantly abolished its HK pro-motility activity. Plasma with added TGFalpha stimulated HK migration that reached more than 80% of the serum stimulation. Since insulin levels are identical between plasma and serum, we propose that TGFalpha is the physiologic HK pro-motility factor in HS.

Cell Movement↗

PubMed2006

Neutrophil-derived leukotriene B4 is required for inflammatory arthritis.

Neutrophils serve as a vanguard of the acute innate immune response to invading pathogens. Neutrophils are also abundant at sites of autoimmune inflammation, such as the rheumatoid joint, although their pathophysiologic role is incompletely defined and relevant effector functions remain obscure. Using genetic and pharmacologic approaches in the K/BxN serum transfer model of arthritis, we find that autoantibody-driven erosive synovitis is critically reliant on the generation of leukotrienes, and more specifically on leukotriene B4 (LTB4), for disease induction as well as perpetuation. Pursuing the cellular source for this mediator, we find via reconstitution experiments that mast cells are a dispensable source of leukotrienes, whereas arthritis susceptibility can be restored to leukotriene-deficient mice by intravenous administration of wild-type neutrophils. These experiments demonstrate a nonredundant role for LTB4 in inflammatory arthritis and define a neutrophil mediator involved in orchestrating the synovial eruption.

Animals↗

PubMed2006

A "traffic control" role for TGFbeta3: orchestrating dermal and epidermal cell motility during wound healing.

Cell migration is a rate-limiting event in skin wound healing. In unwounded skin, cells are nourished by plasma. When skin is wounded, resident cells encounter serum for the first time. As the wound heals, the cells experience a transition of serum back to plasma. In this study, we report that human serum selectively promotes epidermal cell migration and halts dermal cell migration. In contrast, human plasma promotes dermal but not epidermal cell migration. The on-and-off switch is operated by transforming growth factor (TGF) beta3 levels, which are undetectable in plasma and high in serum, and by TGFbeta receptor (TbetaR) type II levels, which are low in epidermal cells and high in dermal cells. Depletion of TGFbeta3 from serum converts serum to a plasmalike reagent. The addition of TGFbeta3 to plasma converts it to a serumlike reagent. Down-regulation of TbetaRII in dermal cells or up-regulation of TbetaRII in epidermal cells reverses their migratory responses to serum and plasma, respectively. Therefore, the naturally occurring plasma-->serum-->plasma transition during wound healing orchestrates the orderly migration of dermal and epidermal cells.

Activin Receptors, Type I↗

PubMed2006

Comparison of the veracity of real-time perfusion, harmonic angio, and ultraharmonic mocardial contrast imaging modes in evaluation of acute myocardial infarction area.

BACKGROUND: Innovative advancements in ultrasound instrumentation present a number of imaging modalities for myocardial contrast echocardiography (MCE) in ischemic syndromes. How well they compare to each other in diagnostic accuracy in the detection of acute myocardial infarction is unclear. The purpose of this study was to assess the relative accuracy of 3 different imaging modes of MCE, low mechanical index (MI) real-time perfusion imaging (RTPI), triggered harmonic angio mode (HA), and ultraharmonic imaging mode (UH) in the detection of acute experimental myocardial infarction within the time frame suitable for potential reperfusion. METHODS: MCE was performed in 10 open-chest dogs using RTPI, triggered HA and triggered UH modes at baseline and one hour after occlusion of left anterior descending coronary artery. Presence or absence of perfusion defects, and the perfusion defect size when present, were analyzed and compared with the infarct size delineated by triphenyltetrazolium chloride (TTC) staining. RESULTS: The infarct area was (15.8 +/- 2.4)% by TTC staining; Perfusion defect area by MCE was similar to anatomic infarct area in all the three MCE approaches: (16.1 +/- 2.7)% by RTPI mode, (15.5 +/- 2.9)% by HA mode, and (15.5 +/- 3.0)% by UH mode. The sensitivity, specificity and overall diagnostic accuracy in the detection of myocardial infarction were 100%, 88%, and 94% for RTPI mode, 88%, 100%, and 94% for HA mode, and 100%, 75%, and 88% for UH mode. CONCLUSION: All modes of MCE, RTPI, triggered HA mode and triggered UH mode have excellent diagnostic accuracy in the immediate hour of acute coronary occlusion within the optimal time frame suitable for reperfusion therapy.

Animals↗

PubMed2006

Klf2 is an essential regulator of vascular hemodynamic forces in vivo.

Hemodynamic responses that control blood pressure and the distribution of blood flow to different organs are essential for survival. Shear forces generated by blood flow regulate hemodynamic responses, but the molecular and genetic basis for such regulation is not known. The transcription factor KLF2 is activated by fluid shear stress in cultured endothelial cells, where it regulates a large number of vasoactive endothelial genes. Here, we show that Klf2 expression during development mirrors the rise of fluid shear forces, and that endothelial loss of Klf2 results in lethal embryonic heart failure due to a high-cardiac-output state. Klf2 deficiency does not result in anemia or structural vascular defects, and it can be rescued by administration of phenylephrine, a catecholamine that raises vessel tone. These findings identify Klf2 as an essential hemodynamic regulator in vivo and suggest that hemodynamic regulation in response to fluid shear stress is required for cardiovascular development and function.

Anemia↗

PubMed2006

PKCdelta clustering at the leading edge and mediating growth factor-enhanced, but not ecm-initiated, dermal fibroblast migration.

We have previously shown that the immobilized extracellular matrices (ECMs) initiate cell migration and soluble growth factors (GFs) further enhance ECM-initiated cell migration. GFs alone cannot initiate cell migration. To further investigate the specificity of the two signaling mechanisms, we focused on the protein kinase C (PKC) family genes in primary human dermal fibroblasts (DFs). We here show that platelet-derived growth factor-BB (PDGF-BB) strongly stimulates membrane translocation and leading edge clustering of protein kinase Cdelta (PKCdelta). In contrast, attachment to collagen matrix alone does not cause the translocation. Although the kinase function of PKCdelta is dispensable for initial membrane translocation, it is critical for its sustained presence at the cells's leading edge. Blockade of endogenous PKCdelta signaling with dominant-negative kinase-defective PKC (PKCdelta-KD) or PKCdelta-small interfering RNA (siRNA) completely inhibited PDGF-BB-stimulated DF migration. In contrast, neither PKCdelta-KD nor PKCdelta-siRNA affected collagen-induced initiation of DF migration. Overexpression of a constitutively activated PKCdelta (PKCdelta-R144/145A) partially mimics the effect of PDGF-BB. However, PKCdelta-KD, PKCdelta-siRNA, or PKCdelta-R144/145A does not affect PDGF-BB-stimulated activation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase1/2, or c-Jun N-terminal kinase. Instead, inhibition of PKCdelta blocks PDGF-BB-stimulated activation of signal transducer and activator of transcription 3 (Stat3). This study unveiled the specificity of PKCdelta in the control of DF migration.

Becaplermin↗

PubMed2006

Fibroblasts as target cells for DEB gene therapy.

Dystrophic epidermolysis bullosa (DEB) is due to mutations in the type VII collagen (C7) gene. Potential therapies for DEB include (i) ex vivo gene therapy and (ii) intradermal injection of gene-corrected DEB fibroblasts, lentiviral vectors expressing C7 or recombinant C7 itself. With regard to molecular engineering, the dermal fibroblast has advantages over epidermal keratinocytes for delivering C7 to DEB patients.

Animals↗

PubMed2006

Induction of epidermolysis bullosa acquisita in mice by passive transfer of autoantibodies from patients.

Epidermolysis bullosa acquisita (EBA) is an autoimmune sub-epidermal blistering disease characterized by autoantibodies to type VII (anchoring fibril) collagen. To date, however, direct evidence for a pathogenic role of human EBA autoantibodies has not been demonstrated. In this study, we affinity-purified anti-type VII collagen antibodies from EBA patients' sera and then injected them into adult hairless immunocompetent mice. Mice injected with EBA autoantibodies developed skin fragility, blisters, erosions, and nail loss on their paws - all features of EBA patients. By clinical, histological, immunological, and ultrastructural parameters, the induced lesions were reminiscent of human EBA. Histology showed bullous lesions with an epidermal-dermal separation. IgG and C3 deposits were observed at the epidermal-dermal junction. All mice had serum antibodies that labeled the dermal side of salt-split human skin like EBA sera. Direct immunogold electron microscopy specifically localized deposits of human IgG to anchoring fibrils. (Fab')(2) fragments generated from EBA autoantibodies did not induce disease. We conclude that EBA human patient autoantibodies cause sub-epidermal blisters and induce EBA skin lesions in mice. These passive transfer studies demonstrate that human EBA autoantibodies are pathogenic. This novel EBA mouse model can be used to further investigate EBA autoimmunity and to develop possible therapies.

Animals↗

PubMed2006

Protein-protein interactions of tandem affinity purification-tagged protein kinases in rice.

Forty-one rice cDNAs encoding protein kinases were fused to the tandem affinity purification (TAP) tag and expressed in transgenic rice plants. The TAP-tagged kinases and interacting proteins were purified from the T1 progeny of the transgenic rice plants and identified by mass spectrometry. Ninety-five percent of the TAP-tagged kinases were recovered. Fifty-six percent of the TAP-tagged kinases were found to interact with other rice proteins. A number of these interactions were consistent with known protein complexes found in other species, validating the TAP-tag method in rice plants. Phosphorylation sites were identified on four of the kinases that interacted with either 14-3-3 proteins or cyclins.

14-3-3 Proteins↗

PubMed2006

Protection elicited by two glutamine auxotrophs of Mycobacterium tuberculosis and in vivo growth phenotypes of the four unique glutamine synthetase mutants in a murine model.

We generated four individual glutamine synthetase (GS) mutants (DeltaglnA1, DeltaglnA2, DeltaglnA3, and DeltaglnA4) and one triple mutant (DeltaglnA1EA2) of Mycobacterium tuberculosis to investigate the roles of GS enzymes. Subcutaneous immunization with the DeltaglnA1EA2 and DeltaglnA1 glutamine auxotrophic mutants conferred protection on C57BL/6 mice against an aerosol challenge with virulent M. tuberculosis, which was comparable to that provided by Mycobacterium bovis BCG vaccination.

Animals↗

PubMed2005

Cytochrome P-450 4F18 is the leukotriene B4 omega-1/omega-2 hydroxylase in mouse polymorphonuclear leukocytes: identification as the functional orthologue of human polymorphonuclear leukocyte CYP4F3A in the down-regulation of responses to LTB4.

Leukotriene B(4) (LTB(4)) is a potent chemoattractant for polymorphonuclear leukocytes (PMN) and other cells. Human PMN inactivate LTB(4) by omega-oxidation catalyzed by cytochrome P-450 (CYP) 4F3A. The contribution of the enzymatic inactivation of LTB(4) by CYP4Fs to down-regulating functional responses of cells to LTB(4) is unknown. To elucidate the role of CYP4F-mediated inactivation of LTB(4) in terminating the responses of PMN to LTB(4) and to identify a target for future genetic studies in mice, we have identified the enzyme that catalyzes the omega-1 and omega-2 oxidation of LTB(4) in mouse myeloid cells as CYP4F18. As determined by mass spectrometry, this enzyme catalyzes the conversion of LTB(4) to 19-OH LTB(4) and to a lesser extent 18-OH LTB(4). Inhibition of CYP4F18 resulted in a marked increase in calcium flux and a 220% increase in the chemotactic response of mouse PMN to LTB(4). CYP4F18 expression was induced in bone marrow-derived dendritic cells by bacterial lipopolysaccharide, a ligand for TLR4, and by poly(I.C), a ligand for TLR3. However, when bone marrow-derived myeloid dendritic cells trafficked to popliteal lymph nodes from paw pads, the expression of CYP4F18 was down-regulated. The results identify CYP4F18 as a critical protein in the regulation of LTB(4) metabolism and functional responses in mouse PMN and identify it as the functional orthologue of human PMN CYP4F3A.

Animals↗

PubMed2005

Human lactoferrin exerts bi-directional actions on PC12 cell survival via ERK1/2 pathway.

Human lactoferrin (hLF) is a member of the transferrin family and is found in most body fluids of human. Recent study showed that hLF played some roles in the regulation of cell growth. However, the biological function of hLF in the central nervous system and neuronal cells is still unclear. The MTT was used to assay cell viability, ELISA tests were used to assay caspase activities, and TUNEL staining was used to test the cytotoxicity of hLF to the cells. Our result showed that 700 microg/ml hLF significantly reduced the cell viability and increased the caspase 3 and 8 activities in PC12 neuronal cells. TUNEL staining further showed that 700 microg/ml hLF was cytotoxic to the PC12 through apoptosis-mediated pathway. In addition, 700 microg/ml hLF significantly decreased the protein expressions of phosphorylated extracellular-signal-regulated kinase 1/2 (ERK1/2) and Bcl-2 in PC12 cells, whereas 50 microg/ml hLF significantly increased the phosphorylation of ERK1/2 which could be specifically inhibited by PD98059. Furthermore, 50 microg/ml hLF could not only up-regulate the Bcl-2 expression but also protect PC12 cells from FasL-induced apoptosis. In conclusion, hLF plays a crucial role in the regulation of apoptosis and anti-apoptosis in PC12 neuronal cells via ERK1/2 phosphorylation pathway.

Animals↗