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Xiang-Jun Chen

Bio: Xiang-Jun Chen is an academic researcher from Tsinghua University. The author has contributed to research in topics: Crystallin & Lanosterol. The author has an hindex of 12, co-authored 23 publications receiving 754 citations. Previous affiliations of Xiang-Jun Chen include Sichuan University & Zhejiang University.

Papers
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Journal ArticleDOI
30 Jul 2015-Nature
TL;DR: In this paper, the authors identify two distinct homozygous LSS missense mutations (W581R and G588S) in two families with extensive congenital cataracts.
Abstract: The human lens is comprised largely of crystallin proteins assembled into a highly ordered, interactive macro-structure essential for lens transparency and refractive index. Any disruption of intra- or inter-protein interactions will alter this delicate structure, exposing hydrophobic surfaces, with consequent protein aggregation and cataract formation. Cataracts are the most common cause of blindness worldwide, affecting tens of millions of people1, and currently the only treatment is surgical removal of cataractous lenses. The precise mechanisms by which lens proteins both prevent aggregation and maintain lens transparency are largely unknown. Lanosterol is an amphipathic molecule enriched in the lens. It is synthesized by lanosterol synthase (LSS) in a key cyclization reaction of a cholesterol synthesis pathway. Here we identify two distinct homozygous LSS missense mutations (W581R and G588S) in two families with extensive congenital cataracts. Both of these mutations affect highly conserved amino acid residues and impair key catalytic functions of LSS. Engineered expression of wild-type, but not mutant, LSS prevents intracellular protein aggregation of various cataract-causing mutant crystallins. Treatment by lanosterol, but not cholesterol, significantly decreased preformed protein aggregates both in vitro and in cell-transfection experiments. We further show that lanosterol treatment could reduce cataract severity and increase transparency in dissected rabbit cataractous lenses in vitro and cataract severity in vivo in dogs. Our study identifies lanosterol as a key molecule in the prevention of lens protein aggregation and points to a novel strategy for cataract prevention and treatment.

331 citations

Journal ArticleDOI
03 Jan 2013-Nature
TL;DR: This study provides a new regulatory mechanism of Ca2+ to T-cell activation involving direct lipid manipulation that has a positive feedback effect on amplifying and sustaining CD3 phosphorylation and should enhance T- cell sensitivity to foreign antigens.
Abstract: Ionic protein-lipid interactions are critical for the structure and function of membrane receptors, ion channels, integrins and many other proteins. However, the regulatory mechanism of these interactions is largely unknown. Here we show that Ca(2+) can bind directly to anionic phospholipids and thus modulate membrane protein function. The activation of T-cell antigen receptor-CD3 complex (TCR), a key membrane receptor for adaptive immunity, is regulated by ionic interactions between positively charged CD3e/ζ cytoplasmic domains (CD3(CD)) and negatively charged phospholipids in the plasma membrane. Crucial tyrosines are buried in the membrane and are largely protected from phosphorylation in resting T cells. It is not clear how CD3(CD) dissociates from the membrane in antigen-stimulated T cells. The antigen engagement of even a single TCR triggers a Ca(2+) influx and TCR-proximal Ca(2+) concentration is higher than the average cytosolic Ca(2+) concentration. Our biochemical, live-cell fluorescence resonance energy transfer and NMR experiments showed that an increase in Ca(2+) concentration induced the dissociation of CD3(CD) from the membrane and the solvent exposure of tyrosine residues. As a consequence, CD3 tyrosine phosphorylation was significantly enhanced by Ca(2+) influx. Moreover, when compared with wild-type cells, Ca(2+) channel-deficient T cells had substantially lower levels of CD3 phosphorylation after stimulation. The effect of Ca(2+) on facilitating CD3 phosphorylation is primarily due to the charge of this ion, as demonstrated by the fact that replacing Ca(2+) with the non-physiological ion Sr(2+) resulted in the same feedback effect. Finally, (31)P NMR spectroscopy showed that Ca(2+) bound to the phosphate group in anionic phospholipids at physiological concentrations, thus neutralizing the negative charge of phospholipids. Rather than initiating CD3 phosphorylation, this regulatory pathway of Ca(2+) has a positive feedback effect on amplifying and sustaining CD3 phosphorylation and should enhance T-cell sensitivity to foreign antigens. Our study thus provides a new regulatory mechanism of Ca(2+) to T-cell activation involving direct lipid manipulation.

208 citations

Journal ArticleDOI
10 Aug 2015-eLife
TL;DR: The mechanical force sensitivity and threshold that are required to activate different isotyped BCRs are defined and it is found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold.
Abstract: B lymphocytes use B cell receptors (BCRs) to sense the physical features of the antigens. However, the sensitivity and threshold for the activation of BCRs resulting from the stimulation by mechanical forces are unknown. Here, we addressed this question using a double-stranded DNA-based tension gauge tether system serving as a predefined mechanical force gauge ranging from 12 to 56 pN. We observed that IgM-BCR activation is dependent on mechanical forces and exhibits a multi-threshold effect. In contrast, the activation of isotype-switched IgG- or IgE-BCR only requires a low threshold of less than 12 pN, providing an explanation for their rapid activation in response to antigen stimulation. Mechanistically, we found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold. These results defined the mechanical force sensitivity and threshold that are required to activate different isotyped BCRs.

81 citations

Journal ArticleDOI
TL;DR: It was found that the knockdown of CKB induced G2 arrest in cell cycle by elevating p21 expression and affected the PI3K/Akt and AMPK pathways, suggesting that CKB depletion/inhibition in combination with chemotherapeutic agents might have synergistic effects in ovarian cancer therapy.

50 citations

Journal ArticleDOI
TL;DR: A quantitative assay applicable to efficacy validations and mechanistic studies by a protocol to isolate protein aggregates from the surgically removed cataractous human lens showed that both compounds were effective for human cataracts samples with EC50 values at ten micromolar level.

32 citations


Cited by
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Journal ArticleDOI
31 Mar 2016-Nature
TL;DR: A new mechanism by which the antitumour response of mouse CD8+ T cells can be potentiated by modulating cholesterol metabolism is reported, which indicates ACAT1, an established target for atherosclerosis, is therefore also a potential target for cancer immunotherapy.
Abstract: CD8(+) T cells have a central role in antitumour immunity, but their activity is suppressed in the tumour microenvironment. Reactivating the cytotoxicity of CD8(+) T cells is of great clinical interest in cancer immunotherapy. Here we report a new mechanism by which the antitumour response of mouse CD8(+) T cells can be potentiated by modulating cholesterol metabolism. Inhibiting cholesterol esterification in T cells by genetic ablation or pharmacological inhibition of ACAT1, a key cholesterol esterification enzyme, led to potentiated effector function and enhanced proliferation of CD8(+) but not CD4(+) T cells. This is due to the increase in the plasma membrane cholesterol level of CD8(+) T cells, which causes enhanced T-cell receptor clustering and signalling as well as more efficient formation of the immunological synapse. ACAT1-deficient CD8(+) T cells were better than wild-type CD8(+) T cells at controlling melanoma growth and metastasis in mice. We used the ACAT inhibitor avasimibe, which was previously tested in clinical trials for treating atherosclerosis and showed a good human safety profile, to treat melanoma in mice and observed a good antitumour effect. A combined therapy of avasimibe plus an anti-PD-1 antibody showed better efficacy than monotherapies in controlling tumour progression. ACAT1, an established target for atherosclerosis, is therefore also a potential target for cancer immunotherapy.

580 citations

Journal ArticleDOI
18 Apr 2019-Cell
TL;DR: How basic research is informing efforts to generate vaccines that induce broadly neutralizing antibodies against viral pathogens is discussed, revealing the special features associated with allergen-reactive IgE responses and uncovering the antibody-independent mechanisms by which B cells contribute to health and disease.

443 citations

Journal ArticleDOI
TL;DR: A molecular model for initiation of T cell receptor signaling is proposed that may serve as a useful guide for future studies and review the current knowledge of models and crucial molecules that aim to provide a mechanistic explanation for these observations.
Abstract: The initiation of T cell antigen receptor signaling is a key step that can result in T cell activation and the orchestration of an adaptive immune response. Early events in T cell receptor signaling can distinguish between agonist and endogenous ligands with exquisite selectivity, and show extraordinary sensitivity to minute numbers of agonists in a sea of endogenous ligands. We review our current knowledge of models and crucial molecules that aim to provide a mechanistic explanation for these observations. Building on current understanding and a discussion of unresolved issues, we propose a molecular model for initiation of T cell receptor signaling that may serve as a useful guide for future studies.

307 citations

Journal ArticleDOI
TL;DR: Tsokos reviews how the genetic, epigenetic and microbial environments influence innate and adaptive immune cells to drive immunopathology and organ damage in systemic lupus erythematosus.
Abstract: Impressive progress has been made over the last several years toward understanding how almost every aspect of the immune system contributes to the expression of systemic autoimmunity. In parallel, studies have shed light on the mechanisms that contribute to organ inflammation and damage. New approaches that address the complicated interaction between genetic variants, epigenetic processes, sex and the environment promise to enlighten the multitude of pathways that lead to what is clinically defined as systemic lupus erythematosus. It is expected that each patient owns a unique 'interactome', which will dictate specific treatment.

250 citations

Journal ArticleDOI
TL;DR: It is shown that an AI agent using deep learning, and involving convolutional neural networks for diagnostics, risk stratification and treatment suggestions, accurately diagnoses and provides treatment decisions for congenital cataracts in an in silico test, a website-based study, in a ‘finding a needle in a haystack’ test and in a multihospital clinical trial.
Abstract: Using artificial intelligence (AI) to prevent and treat diseases is an ultimate goal in computational medicine. Although AI has been developed for screening and assisted decision-making in disease prevention and management, it has not yet been validated for systematic application in the clinic. In the context of rare diseases, the main strategy has been to build specialized care centres; however, these centres are scattered and their coverage is insufficient, which leaves a large proportion of rare-disease patients with inadequate care. Here, we show that an AI agent using deep learning, and involving convolutional neural networks for diagnostics, risk stratification and treatment suggestions, accurately diagnoses and provides treatment decisions for congenital cataracts in an in silico test, in a website-based study, in a ‘finding a needle in a haystack’ test and in a multihospital clinical trial. We also show that the AI agent and individual ophthalmologists perform equally well. Moreover, we have integrated the AI agent with a cloud-based platform for multihospital collaboration, designed to improve disease management for the benefit of patients with rare diseases. An artificial intelligence agent integrated with a cloud-based platform for multihospital collaboration performs equally as well as ophthalmologists in the diagnosis of congenital cataracts in a series of online tests and a multihospital clinical trial.

248 citations