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Biomedical subjects

Li Gan

Publications and source records attributed to Li Gan.

At least 19 recordsLinked to original sources

Spatial isoform sequencing at single-cell resolution reveals cell-type-specific spatial isoform variability in multiple brain cell types.

Spatial long-read technologies are increasingly common but usually lack single-cell resolution. This leaves unanswered whether spatially variable isoforms reflect variability within one cell type or differences in region-specific cell-type composition. Here, we developed Spl-ISO-Seq2 (500-nm resolution) and accompanying software, Spl-IsoQuant-2 and Spl-IsoFind, enabling long-read sequencing of >450 million barcodes versus 80,000 previously. Applying this to the adult mouse brain, we compared differential isoform abundance between known regions and spatial isoform patterns independent of predefined regions. Both identified overlapping hits, for example, Rps24 in oligodendrocytes. For known Snap25 spatial isoform variation, we show that it occurs in excitatory neurons. The region-agnostic approach also uncovered patterns missed by region-based comparisons, for example, for Ighm. Notably, many spatial isoform signals are not driven by cell-type composition alone. Finally, our software is applicable to many spatial and single-cell protocols, demonstrating reproducibility between platforms (for example, Visium HD/Stereo-seq). Overall, our experimental/analytical methods enable a submicron-resolution-isoform view and open avenues for spatial isoform disease research.

Animals↗

Chaperone-mediated autophagy regulates neuronal activity by sex-specific remodelling of the synaptic proteome.

Chaperone-mediated autophagy (CMA) declines in ageing and neurodegenerative diseases. Loss of CMA in neurons leads to neurodegeneration and behavioural changes in mice but the role of CMA in neuronal physiology is largely unknown. Here we show that CMA deficiency causes neuronal hyperactivity, increased seizure susceptibility and disrupted calcium homeostasis. Pre-synaptic neurotransmitter release and NMDA receptor-mediated transmission were enhanced in CMA-deficient females, whereas males exhibited elevated post-synaptic AMPA-receptor activity. Comparative quantitative proteomics revealed sexual dimorphism in the synaptic proteins degraded by CMA, with preferential remodelling of the pre-synaptic proteome in females and the post-synaptic proteome in males. We demonstrate that genetic or pharmacological CMA activation in old mice and an Alzheimer's disease mouse model restores synaptic protein levels, reduces neuronal hyperexcitability and seizure susceptibility, and normalizes neurotransmission. Our findings unveil a role for CMA in regulating neuronal excitability and highlight this pathway as a potential target for mitigating age-related neuronal decline.

Animals↗

Antiamyloidogenic and neuroprotective functions of cathepsin B: implications for Alzheimer's disease.

Alzheimer's disease (AD) may result from the accumulation of amyloid-beta (Abeta) peptides in the brain. The cysteine protease cathepsin B (CatB) is associated with amyloid plaques in AD brains and has been suspected to increase Abeta production. Here, we demonstrate that CatB actually reduces levels of Abeta peptides, especially the aggregation-prone species Abeta1-42, through proteolytic cleavage. Genetic inactivation of CatB in mice with neuronal expression of familial AD-mutant human amyloid precursor protein (hAPP) increased the relative abundance of Abeta1-42, worsening plaque deposition and other AD-related pathologies. Lentivirus-mediated expression of CatB in aged hAPP mice reduced preexisting amyloid deposits, even thioflavin S-positive plaques. Under cell-free conditions, CatB effectively cleaved Abeta1-42, generating C-terminally truncated Abeta peptides that are less amyloidogenic. Thus, CatB likely fulfills antiamyloidogenic and neuroprotective functions. Insufficient CatB activity might promote AD; increasing CatB activity could counteract the neuropathology of this disease.

Age Factors↗

Cloning, comparative characterization of porcine SCAP gene, and identification of its two splice variants.

Sterol responsive element binding protein (SREBP) cleavage-activating protein (SCAP) is the key regulator of activation of SREBPs, which stimulate most enzymes in cholesterol and lipid synthesis. In order to investigate the molecular basis of lipid metabolism in the pig, a unique model for fat deposition, we isolated and characterized the porcine SCAP. The 4,096-bp full-length porcine SCAP cDNA contains an open reading frame of 3,840 bp. The predicted SCAP protein consists of 1,280 amino acids of 55-92% identity with its vertebrate counterparts. The porcine SCAP gene consists of at least 19 exons and 18 introns, which span over 13 kb of the genome. The porcine SCAP gene was mapped to chromosome 13q21-22 using a porcine-rodent somatic cell hybrid panel. Comparison of SCAP genomic structures from various species revealed intron losses in porcine, Tetraodon and fugu SCAP, and intron gains in cow and chicken SCAP. Moreover, we isolated two novel splicing SCAP variants with 193-bp (variant 2) in-frame deletion from testis and a variant with 291-bp (variant 3) in-frame deletion from liver and muscle, which may affect the function of the porcine SCAP. In conclusion, the intron gains and losses appear to have contributed to the shape of the modern SCAP family. The splice variants detected, first to be reported in any species, may be involved in the particulars of the fat metabolism in the pig. Our data lay foundation for further study of SCAP function in this species.

Alternative Splicing↗

Gene organization, alternate splicing and expression pattern of porcine visfatin gene.

Visfatin is a newly discovered visceral fat-specific adipocytokine. It is upregulated in obesity and exerts insulin-mimetic effects in various tissues in human and mouse. We reported here the cloning and characterization of porcine visfatin, its three alternate splicing variants. Sequence analysis indicated that variant 1 is the predominant form among species, which contains an open reading frame of 1473 bp encoding a 52-kDa protein of 491 amino acids. While the other two variants were predicted to encode two 3' truncated proteins due to early termination. The nucleotide and amino acid sequences deduced from variant 1 were conservative across species. The porcine visfatin gene was composed of 11 exons at least and had exactly the same exon/intron structure as the human orthologs. Nested PCR showed that variants 1 and 3 were ubiquitously expressed in porcine tissues and that variant 2 was expressed in most tissues examined with exception of testis and liver. The discovery of the three variants of visfatin in porcine would be useful to the further investigation of the function of the visfatin gene.

Alternative Splicing↗

Determination of the accessibility of acidic oligosaccharide sugar chain to blood-brain barrier using surface plasmon resonance.

There exist limitations in the detection of exogenous oligosaccharides due to their polydisperse and diversiform nature, and particularly the interference of endogenous glycosaminoglycans (GAGs). Herein, a surface plasmon resonance (SPR) assay for detecting acidic oligosaccharide sugar chain (AOSC), an anti-Alzheimer's drug candidate, in cerebrospinal fluid (CSF) was developed based on a carbohydrate antigen-antibody interaction. Rabbits were treated with AOSC intravenously and orally at 40 or 200 mg x kg(-1), respectively. CSF samples were collected at given time points for quantitative determination of AOSC concentrations in the CSF using an SPR-based competitive inhibition assay, and the existence of AOSC in the CSF was indicated as a blood-brain barrier (BBB) accessibility index. AOSC concentration as low as 50 ppb (0.05 microg x ml(-1)) was detected in the CSF, with its peak value approaching 2.091 and 3.316 microg x ml(-1) following intravenous and oral administration, respectively. This is the first time the capacity of AOSC to pass through the BBB has been confirmed using SPR-based competitive inhibition immunoassay. Importantly, the accessibility of AOSC to the BBB indicates AOSC has potential therapeutic value for treating neurodegenerative diseases, particular Alzheimer's disease.

Administration, Oral↗

SIRT1 protects against microglia-dependent amyloid-beta toxicity through inhibiting NF-kappaB signaling.

Accumulating evidence suggests that neurodegeneration induced by pathogenic proteins depends on contributions from surrounding glia. Here we demonstrate that NF-kappaB signaling in microglia is critically involved in neuronal death induced by amyloid-beta (Abeta) peptides, which are widely presumed to cause Alzheimer disease. Constitutive inhibition of NF-kappaB signaling in microglia by expression of the nondegradable IkappaBalpha superrepressor blocked neurotoxicity, indicating a pivotal role for microglial NF-kappaB signaling in mediating Abeta toxicity. Stimulation of microglia with Abeta increased acetylation of RelA/p65 at lysine 310, which regulates the NF-kappaB pathway. Overexpression of SIRT1 deacetylase and the addition of the SIRT1 agonist resveratrol markedly reduced NF-kappaB signaling stimulated by Abeta and had strong neuroprotective effects. Our results support a glial loop hypothesis by demonstrating a critical role for microglial NF-kappaB signaling in Abeta-dependent neurodegeneration. They also implicate SIRT1 in this pathway and highlight the therapeutic potential of resveratrol and other sirtuin-activating compounds in Alzheimer disease.

Alzheimer Disease↗

Sulfated polymannuroguluronate, a novel anti-AIDS drug candidate, inhibits T cell apoptosis by combating oxidative damage of mitochondria.

Sulfated polymannuroguluronate (SPMG) has entered the phase II clinical trial as the first anti-AIDS drug candidate in China. Herein, we report that SPMG was effective at protecting T lymphocytes against apoptosis. Further studies indicated that SPMG significantly elevated mitochondrial membrane potential (MMP) of T cells; inhibited mitochondrial release of cytochrome c (cyto c) in T cells; enhanced the activities of mitochondrial enzyme complex I, III, and V; and subsequently increased ATP level and ATP/ADP ratio. In addition, SPMG potently suppressed reactive oxygen species (ROS) generation in mitochondria at cellular level and scavenged free radicals in cell-free system. The molecular mechanism underlying the ATP-involved and ROS-dependent antiapoptosis of SPMG is characterized as having been caused by its engagement with mitochondrial import receptor and ADP/ATP carrier in T-cell outer and inner mitochondrial membrane, respectively. All these might shed new light on the understanding of anti-AIDS functions of SPMG by protecting T cells of persons infected with human immunodeficiency virus.

Adenosine Triphosphate↗

Cytology applications of p63 and TTF-1 immunostaining in differential diagnosis of lung cancers.

The pathologic distinction of small cell from non-small cell-lung carcinoma is of considerable therapeutic significance. In particular, the ability to distinguish poorly differentiated non-small-cell lung cancer from small-cell lung carcinoma (SCLC) is at times difficult based upon morphology alone; available immunohistochemical markers such as neuroendocrine markers are of limited utility. We have demonstrated the role of p63 and thyroid transcription factor-1 (TTF-1) in the differential diagnosis of poorly differentiated squamous-cell carcinoma (PDSCC) versus SCLC, mostly in biopsy samples (Wu et al., American Journal of Clinical Pathology 2003;119:696-702). Here, we examine further the utility of this panel in cytologic cell-block samples of lung cancers including both primary and metastatic cancers of pulmonary origin, and cases of nonpulmonary cancers metastatic to lung in which differential diagnoses included a lung primary.Four-micron thick sections of 30 alcohol-fixed paraffin-embedded cell blocks from 14 lung FNAs, 6 liver FNAs, 3 bronchial washings, 1 subcarinal lymph node FNA, 1 iliac lymph node FNA, 1 pelvic mass FNA, 1 neck lymph node FNA, 1 adrenal FNA, and 1 pleural effusion were deparaffinized and stained with monoclonal antibodies reactive to p63 (1:800, Santa Cruz Biotechnology) and TTF-1 (1:50, Dako). Slides were stained for p63 using a streptavidin-biotin kit (BioGenex) and diaminobenzidine as chromagen, and counterstained with hematoxylin. Slides were stained for TTF-1 using a Dako Autostainer. Thirty cases were examined, including 8 primary SCLCs, 8 extra-pulmonary metastases of lung SCLCs, 4 PDSCCs and 4 primary pulmonary adenocarcinomas, and 6 nonpulmonary adenocarcinomas metastatic to lung or other sites. Fifteen out of 16 (94%) SCLC cases were p63-/TTF-1+, ranging in intensity from focal-weak to diffuse-strong; 1/16 SCLCs from a bronchial washing was p63-/TTF-1- but synaptophysin was positive. All 4 primary lung adenocarcinoma cases were p63-/TTF-1+; contrasting with nonpulmonary adenocarcinomas that were all p63-/TTF-1-. All 4 PDSCC cases were p63+/TTF-1-. The panel of p63 and TTF-1 appears to be useful in the diagnostic evaluation of cytologic cell-block samples of pulmonary malignancy.

Adenocarcinoma↗

Characterization of conformational epitope of alginate-derived polymannuronates by surface plasmon resonance.

In the present study, we developed a mAb to alginate-derived polymannuronates (ADPM) and examined the antigenic epitopes using surface plasmon resonance (SPR) in conjunction with a large panel of oligomannuronate probes. We found that tetrasaccharide is the minimum-binding unit, and that increases in chain length from the tetrasaccharide to the heptsaccharide further enhance monovalent binding. A sharp increase in affinity was observed when increasing from the octasaccharide to the cosasaccharide, which is due to a further enhancement of the individual antigenic epitope combined with multivalency. Kinetic binding studies further suggested that the conformational epitope is discontinuous and infrequent and that a C6-carboxyl group is important in maintaining the conformational epitope. Moreover, CD analysis revealed there were conformational structures in epitopes. The data support our hypothesis that the conformational epitope for the mAb may be an extended helical segment of ADPM. ADPM exists mainly in linear form, but it can infrequently and spontaneously form extended helices. Although helices are not prevalent in ADPM, the immune system preferentially selects these conformational epitopes because they are unique. Together, our results indicate that the antigenic epitopes in beta-d-mannuronates are conformational and require C6-carboxyl groups.

Alginates↗

Regulation of the timing of MNTB neurons by short-term and long-term modulation of potassium channels.

The firing patterns of neurons in central auditory pathways encode specific features of sound stimuli, such as frequency, intensity and localization in space. The generation of the appropriate pattern depends, to a major extent, on the properties of the voltage-dependent potassium channels in these neurons. The mammalian auditory pathways that compute the direction of a sound source are located in the brainstem and include the connection from bushy cells in the anteroventral cochlear nucleus (AVCN) to the principal neurons of the medial nucleus of the trapezoid body (MNTB). To preserve the fidelity of timing of action potentials that is required for sound localization, these neurons express several types of potassium channels, including the Kv3 and Kv1 families of voltage-dependent channels and the Slick and Slack sodium-dependent channels. These channels determine the pattern of action potentials and the amount of neurotransmitter released during repeated stimulation. The amplitude of currents carried by one of these channels, the Kv3.1b channel, is regulated in the short term by protein phosphorylation, and in the long term, by changes in gene expression, such that the intrinsic excitability of the neurons is constantly being regulated by the ambient auditory environment.

Action Potentials↗

Immunocytochemical detection of XIAP in body cavity effusions and washes.

Body cavity effusions may be the first manifestation of malignancy or of recurrence or relapse. We surveyed effusions and washes for expression of X-linked inhibitor of apoptosis (XIAP), a potent constituent of the inhibitor of apoptosis (IAP) family of proteins. IAPs prevent apoptosis by blocking the activation of caspases, thereby preventing caspase-mediated cell degradation. Elevated expression of XIAP could be an underpinning of relapse and/or resistance to apoptosis-inducing cancer therapy. We performed an immunocytochemical survey of XIAP expression in cell blocks from benign and malignant body cavity effusions and washes. In all, 116 alcohol-fixed, formalin postfixed paraffin-embedded cell block specimens from 82 pleural effusions, 22 ascites, 11 pelvic/peritoneal washes and one pericardial effusion were evaluated immunocytochemically with monoclonal anti-XIAP (#610763, BD Biosciences, San Jose, USA) 1:250, 4 degrees C x 72 h, and developed using EnVision-Plus reagents (Dako) and diaminobenzidine as chromagen. Particulate cytoplasmic staining was considered positive. The prevalence of staining for specific malignancies varied with the tissue of origin as follows: ovarian (13/13, 100%); lung (9/11, 82%), breast (6/13, 46%); gastric (4/7, 57%), colon (0/4, 0%), pancreas (2/3, 67%), gallbladder (1/1, 100%), fallopian tube (1/3, 33%), endometrial (6/7, 86%), mesothelioma (4/5, 80%), carcinoma of unknown primary (5/5, 100%) and hematopoietic malignancies (3/9, 33%). Overall, 54 out of 81 (67%) malignant effusions displayed XIAP positivity. Benign effusions (n = 35) were virtually XIAP-negative except for two cases (6%) in which histiocytes showed moderate staining. Weak nonspecific staining was sometimes noted in inflammatory cells or histiocytes. XIAP immunostaining, when strong, allows for ready distinction of malignant from benign and reactive cell populations. Strong XIAP staining was most prevalent in ovarian carcinomas and less prevalent in mammary carcinomas. The degree of XIAP staining of tumor cells may be a means of identifying the most therapy-resistant cases (ie, those with strong XIAP expression), and allow additional triaging to XIAP-blocking drugs presently being developed and clinically tested.

Apoptosis↗

New non-viral method for gene transfer into primary cells.

The availability of genetically altered cells is an essential prerequisite for many scientific and therapeutic applications including functional genomics, drug development, and gene therapy. Unfortunately, the efficient gene transfer into primary cells is still problematic. In contrast to transfections of most cell lines, which can be successfully performed using a variety of methods, the introduction of foreign DNA into primary cells requires a careful selection of gene transfer techniques. Whereas viral strategies are time consuming and involve safety risks, non-viral methods proved to be inefficient for most primary cell types. The Nucleofector technology is a novel gene transfer technique designed for primary cells and hard-to-transfect cell lines. This non-viral gene transfer method is based on a cell type specific combination of electrical parameters and solutions. In this report, we show efficient transfer of DNA expression vectors and siRNA oligonucleotides into a variety of primary cell types from different species utilizing the Nucleofector technology, including human B-CLL cells, human CD34+ cells, human lymphocytes, rat cardiomyocytes, human, porcine, and bovine chondrocytes, and rat neurons.

Animals↗

Intracellularly generated amyloid-beta peptide counteracts the antiapoptotic function of its precursor protein and primes proapoptotic pathways for activation by other insults in neuroblastoma cells.

Most mutations in amyloid precursor proteins (APPs) linked to early onset familial Alzheimer's disease (FAD) increase the production of amyloid-beta peptides ending at residue 42 (Abeta42), which are released from APP by beta- and gamma-secretase cleavage. Stably transfected cells expressing wild-type human APP (APP(WT)) were more resistant to apoptosis-inducing treatments than cells expressing FAD-mutant human APP (APP(FAD)). Preventing Abeta42 production with an M596I mutation (beta-), which blocks beta-secretase cleavage of APP, or by treatment with a gamma-secretase inhibitor increased the resistance of APP(FAD)-expressing cells to apoptosis. Exposing hAPP(FAD/beta-) cells to exogenous Abeta42 or conditioned medium from Abeta42-producing APP(FAD) cells did not diminish their resistance to apoptosis. Preventing APP from entering the distal secretory pathway, where most Abeta peptides are generated, by retaining APP in the endoplasmic reticulum (ER)/intermediate compartment (IC) increased the resistance of APP(FAD)-expressing cells to apoptosis and did not alter the resistance of APP(WT)-expressing cells. p53-mediated gene transactivation after apoptosis-inducing treatments was much stronger in APP(FAD) cells than in hAPP(WT) or hAPP(FAD/beta-) cells. In contrast, upon induction of ER stress, cells expressing APP(FAD), hAPP(FAD/beta-), or APP(WT) had comparable levels of glucose-regulated protein-78 mRNA, an unfolded protein response indicator. We conclude that Abeta, especially intracellular Abeta, counteracts the antiapoptotic function of its precursor protein and predisposes cells to p53-mediated, and possibly other, proapoptotic pathways.

Alzheimer Disease↗

Immunogenic comparison of two coupling methods of marine polysaccharide to bovine serum albumin.

Two conjugates of marine polysaccharide (MPS) and bovine serum albumin (BSA) were prepared using two methods, periodate oxidation and reductive amination, with the intent of enhancing its immunogenicity. Sera samples from Balb/c mice immunized with the products named MPS-BSAp and MPS-BSAr respectively were evaluated by enzyme-linked-immunosorbent assay (ELISA). The results showed that mice immunized with MPS-BSAp produced antibodies not against MPS but rather against MPS-BSAp, while the mice immunized with MPS-BSAr produced high titer antibodies only specific for MPS. The difference was attributed to the fact that the epitopes of MPS had been changed in the coupling process by periodate oxidation. A mouse immunized with MPS-BSAr was chosen to prepare monoclonal antibodies (mAbs) specific for polysaccharide MPS. A hybridoma cell line that secreted monoclonal antibody recognizing specifically polysaccharide MPS was established.

Animals↗

Identification of cathepsin B as a mediator of neuronal death induced by Abeta-activated microglial cells using a functional genomics approach.

Alzheimer's disease is a progressive neurodegenerative disease characterized by senile plaques, neurofibrillary tangles, dystrophic neurites, and reactive glial cells. Activated microglia are found to be intimately associated with senile plaques and may play a central role in mediating chronic inflammatory conditions in Alzheimer's disease. Activation of cultured murine microglial BV2 cells by freshly sonicated Abeta42 results in the secretion of neurotoxic factors that kill primary cultured neurons. To understand molecular pathways underlying Abeta-induced microglial activation, we analyzed the expression levels of transcripts isolated from Abeta42-activated BV2 cells using high density filter arrays. The analysis of these arrays identified 554 genes that are transcriptionally up-regulated by Abeta42 in a statistically significant manner. Quantitative reverse transcription-PCR was used to confirm the regulation of a subset of genes, including cysteine proteases cathepsin B and cathepsin L, tissue inhibitor of matrix metalloproteinase 2, cytochrome c oxidase, and allograft inflammatory factor 1. Small interfering RNA-mediated silencing of the cathepsin B gene in Abeta-activated BV2 cells diminished the microglial activation-mediated neurotoxicity. Moreover, CA-074, a specific cathepsin B inhibitor, also abolished the neurotoxic effects caused by Abeta42-activated BV2 cells. Our results suggest an essential role for secreted cathepsin B in neuronal death mediated by Abeta-activated inflammatory response.

Alzheimer Disease↗

Neuregulin-1 suppresses muscarinic receptor expression and acetylcholine-activated muscarinic K+ channels in cardiac myocytes.

The neuregulin-1 family of growth factors regulates nicotinic acetylcholine receptor synthesis in skeletal muscle, but its role in cardiac myogenesis remains unclear. Here, we investigate the involvement of neuregulins in the development of cardiac cholinergic responsiveness. Treatment of chick cardiac myocytes with neuregulin-1 inhibited mRNA expression of the M4 muscarinic receptor, but not the M2 receptor. In addition, mRNA levels of GIRK1 were reduced in myocytes by treatment with neuregulin-1. Activation of cholinergic receptors in cultured chick atrial myocytes by carbachol produced an outward potassium current (I(K(ACh))), which was attenuated by 24-48-h pre-treatment with neuregulin-1. These data suggest that neuregulins can regulate cardiac parasympathetic tone and may be involved in the pathogenesis of cardiac arrhythmias and heart failure.

Acetylcholine↗

Expression of p63 in papillary thyroid carcinoma and in Hashimoto's thyroiditis: a pathobiologic link?

p63 proteins are p53 homologs that are postulated to regulate squamous stem cell commitment. An immunohistochemical survey of p63 expression in normal thyroid and in reactive, neoplastic, and inflammatory thyroid disorders was performed. Sections from routinely fixed and processed archival thyroidectomy specimens were pretreated with citric acid, pH 6.0, for antigen retrieval, then incubated overnight with anti-p63 monoclonal antibody 4A4. Slides were stained using a streptavidin-biotin kit and diaminobenzidine as a chromagen, and then were counterstained with hematoxylin. The results showed that p63 expression was negative in normal thyroid tissue, nodular goiters, and oncocytic follicular adenomas. Positivity was rare and weak in follicular adenomas. p63-positive foci were commonly found in Hashimoto's thyroiditis (1 or more foci in 78.8% of cases), but rare in Graves' disease. Twenty-seven of 33 papillary thyroid carcinomas (81.8%) displayed p63-positive foci. Staining was uncommon in follicular carcinomas and rare in medullary carcinomas. One case of insular carcinoma was p63-positive. All squamoid structures were p63-positive; p63-positive structures morphologically consistent with solid cell nests were also identified. Based on the results of this study, we conclude that p63 is commonly expressed in papillary thyroid carcinoma and in Hashimoto's thyroiditis. Given the debated association of papillary thyroid carcinoma with Hashimoto's thyroiditis, it is possible that p63 expression may be a potential pathobiologic link between the two disorders. The finding of p63 in benign squamoid nests supports a possible interrelationship between these structures and both Hashimoto's thyroiditis and papillary carcinoma. The high percentage of papillary carcinomas with p63-positive foci appears to distinguish papillary carcinoma from other neoplasms originating in the thyroid.

Adenocarcinoma, Papillary↗