Biomedical subjects

Mi Li

Publications and source records attributed to Mi Li.

10 recordsLinked to original sources

PubMed2025

The impact of m6A methyltransferase METTL3 on airway remodeling in bronchial asthma.

BACKGROUND: Methyltransferase-like 3 (METTL3) is known to play a role in asthma airway remodeling and cell proliferation. Adenylate kinase 4 (AK4) regulates the proliferation of pulmonary artery smooth muscle cells and exerts its effects through the protein kinase B (AKT) pathway. However, the role of METTL3 and AK4-AKT in bronchial smooth muscle cells remains unclear. METHODS: Systemic METTL3 knockout mice and a mouse model of asthma were established. Airway remodeling was assessed using pulmonary function tests, histopathological staining, and Western blot analysis. RNA sequencing (RNA-seq) was performed to detect changes in gene expression following METTL3 knockdown. The 5-ethynyl-2'-deoxyuridine (EdU) assay was used to evaluate cell proliferation. Finally, the expression levels of relevant proteins were validated by Western blotting. RESULTS: Compared with the control model group, the METTL3 knockout group showed significantly reduced inflammatory cell infiltration, decreased collagen fiber deposition, and attenuated airway smooth muscle hyperplasia. RNA-seq revealed that the expression of numerous proliferation-related genes, including AK4, was upregulated following METTL3 knockdown. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that these genes were primarily enriched in the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway. The EdU assay demonstrated that METTL3 knockdown inhibited cell proliferation. Western blot validation showed increased AK4 expression in lung tissues of the METTL3 knockout group compared to the control group, while phosphorylated AKT (p-AKT) levels were reduced. CONCLUSIONS: METTL3 knockout inhibits airway smooth muscle hyperplasia and alleviates airway remodeling in asthma. This effect may be mediated through the regulation of AK4 and the AKT signaling pathway.

Airway Remodeling↗

PubMed2003

Retention of sequential drug discriminations under fixed-interval schedules for long time periods without training.

The experiments showed that sequential drug discriminations can be learned and retained under a fixed-interval (FI) schedule for more than 18 months without additional training under a complex three-choice procedure. Pigeons were trained to discriminate among 5 mg/kg pentobarbital, 2 mg/kg D-amphetamine, and saline. After responding stabilized, dose-response curves were determined for other drugs. Subsequently, pentobarbital was replaced with 5 mg/kg morphine as a training drug, and D-amphetamine was replaced with 30 mg/kg caffeine. After the pigeons learned these new discriminations, dose-response curves were redetermined. Initially, chlordiazepoxide substituted for pentobarbital, cocaine substituted for D-amphetamine, and nicotine partially substituted for D-amphetamine. Morphine, Delta9-tetrahydrocannabinol, and caffeine did not substitute for either drug. After retraining with morphine and caffeine, responding occurred on the pentobarbital/morphine key after pentobarbital, chlordiazepoxide and morphine and on the D-amphetamine/caffeine key after D-amphetamine, cocaine and caffeine. After nicotine and Delta9-tetrahyrdocannabinol, responding occurred on the saline key. These data show that drug discriminations learned under fixed-interval schedules are retained for long time periods, even when discrimination training with other drugs occurs during the retention period.

Animals↗

PubMed2003

Characterization of four orthologs of stringent starvation protein A.

Orthologous proteins can be beneficial for X-ray crystallographic studies when a protein from an organism of choice fails to crystallize or the crystals are not suitable for structure determination. Their amino-acid sequences should be similar enough that they will share the same fold, but different enough so that they may crystallize under alternative conditions and diffract to higher resolution. This multi-species approach was employed to obtain diffraction-quality crystals of the RNA polymerase (RNAP) associated stringent starvation protein A (SspA). Although Escherichia coli SspA could be crystallized, the crystals failed to diffract well enough for structure determination. Therefore, SspA proteins from Yersinia pestis, Vibrio cholerae and Pseudomonas aeruginosa were cloned, expressed, purified and subjected to crystallization trials. The V. cholerae SspA protein failed to crystallize under any conditions tested and the P. aeruginosa SspA protein did not form crystals suitable for data collection. On the other hand, Y. pestis SspA crystallized readily and the crystals diffracted to 2.0 A.

Amino Acid Sequence↗

PubMed2003

Structural and enzymatic properties of the sedolisin family of serine-carboxyl peptidases.

Sedolisins (serine-carboxyl peptidases) are proteolytic enzymes whose fold resembles that of subtilisin; however, they are considerably larger, with the mature catalytic domains containing approximately 375 amino acids. The defining features of these enzymes are a unique catalytic triad, Ser-Glu-Asp, as well as the presence of an aspartic acid residue in the oxyanion hole. High-resolution crystal structures have now been solved for sedolisin from Pseudomonas sp. 101, as well as for kumamolisin from a thermophilic bacterium, Bacillus novo sp. MN-32. The availability of these crystal structures enabled us to model the structure of mammalian CLN2, an enzyme which, when mutated in humans, leads to a fatal neurodegenerative disease. This review compares the structural and enzymatic properties of this newly defined MEROPS family of peptidases, S53, and introduces their new nomenclature.

Amino Acid Sequence↗

PubMed2003

[The changes of angiotensin II receptor expression in cardiomyocytes of ventricles in pigs with experimental ventricular septal defect].

OBJECTIVE: To investigate the changes of angiotensin II receptors expression in cardiomyocytes of both ventricles in pigs with experimental ventricular septal defect (VSD). METHODS: Nineteen young pigs were divided into 3 groups: the pigs that received operation to produce experimental VSD, the pigs that underwent sham-operation, and the pigs as normal control. One month after the operation, the pigs were catheterized and then put to death; the cardiomyocytes were taken from their ventricles and were isolated. Radioligand binding assay was done to measure the Bmax and KD of angiotensin II receptor per 10(6) cells. RESULTS: For both Bmax and KD of angiotensin II receptors, there were no significant differences between the sham-operation group and the control. The Bmax of left ventricle AT1R (188.42 +/- 133.97 fmol/10(6)) and Bmax of right ventricle AT1R (272.14 +/- 232.74 fmol/10(6)) and AT2R (40.42 +/- 34.76 fmol/10(6)) in the operation group were significantly elevated in comparison with the control (Bmax of left ventricle AT1R 29.20 +/- 19.50 fmol/L, and Bmax of right ventricle AT1R 76.72 +/- 51.21 fmol/L and AT2R 9.63 +/- 1.27 fmol/L) respectively, P < 0.05. CONCLUSION: Intracardiac left-to-right shunt related volume overload leads to the elevation of AT1R expression in cardiomyocytes, which serves as an important mechanism of ventriclular hypertrophy and remodling in congenital heart disease. The increased expression of AT2R in right ventricle is a possible explanation of the phenomenon that moderately sized VSDs usually show left other than right ventriclular hypertrophy, taking into account that AT2R has been suggested to mediate antitrophic reaction.

Animals↗

PubMed2002

Structural basis for the substrate specificity of tobacco etch virus protease.

Because of its stringent sequence specificity, the 3C-type protease from tobacco etch virus (TEV) is frequently used to remove affinity tags from recombinant proteins. It is unclear, however, exactly how TEV protease recognizes its substrates with such high selectivity. The crystal structures of two TEV protease mutants, inactive C151A and autolysis-resistant S219D, have now been solved at 2.2- and 1.8-A resolution as complexes with a substrate and product peptide, respectively. The enzyme does not appear to have been perturbed by the mutations in either structure, and the modes of binding of the product and substrate are virtually identical. Analysis of the protein-ligand interactions helps to delineate the structural determinants of substrate specificity and provides guidance for reengineering the enzyme to further improve its utility for biotechnological applications.

Amino Acid Sequence↗

PubMed2002

The discrimination of drug mixtures using a four-choice procedure in pigeons.

RATIONALE: The purpose of these experiments was to study drug combinations as discriminative stimuli using a new four-choice procedure. OBJECTIVES: To determine whether pigeons could discriminate among a mixture of two drugs, each of the component drugs and saline, and to study other drug combinations in these birds. METHODS: Pigeons were trained to discriminate among saline, 5 mg/kg morphine, 5 mg/kg pentobarbital, and a mixture of these two doses using a four-choice procedure. RESULTS: When responding stabilized, the birds responded on the correct key more than 90% of the time. Low doses of all drugs given alone produced responding on the saline key. Higher doses of pentobarbital and chlordiazepoxide produced responding on the pentobarbital key, and higher doses of morphine produced responses on the morphine key. Methamphetamine produced responding on the saline key. None of the drugs given alone produced responding on the mixture key. When pentobarbital was combined with morphine, doses both below and above the combined training doses of these drugs usually produced responding on the mixture key. The combination of chlordiazepoxide with morphine produced similar results. Combinations of methamphetamine with pentobarbital or with morphine produced effects similar to those of pentobarbital or morphine given alone. CONCLUSIONS: A wide range of combinations of pentobarbital and morphine, or chlordiazepoxide and morphine produce responding on the mixture key, even though the pigeons were not exposed to these dose combinations during training. The four-choice procedure provides the opportunity to study drug mixtures in a detail not possible with more limited response choices.

Animals↗

PubMed2002

An unusual orientation for Tyr75 in the active site of the aspartic proteinase from Saccharomyces cerevisiae.

The structures of the native Saccharomyces cerevisiae proteinase A have been solved by molecular replacement in the monoclinic and trigonal crystal forms and refined at 2.6-2.7A resolution. These structures agree overall with those of other uninhibited aspartic proteinases. However, an unusual orientation for the side chain of Tyr75, a conserved residue on the flexible "flap" that covers the active site and is important for the activity of these enzymes, was found in the trigonal crystals. A similar conformation of Tyr75 occupying the S1 substrate-binding pocket was previously reported only for chymosin (where it was interpreted as representing a "self-inhibited" state of the enzyme), but for no other aspartic proteinases. Since this orientation of Tyr75 has now been seen in the structures of two members of the family of aspartic proteinases, it might indicate that the placement of that residue in the S1 substrate-binding pocket might have some functional significance, analogous to what was seen for self-inhibited structures of serine proteinases.

Aspartic Acid Endopeptidases↗

PubMed2002

Pharmacokinetic antagonism of (+)-methamphetamine discrimination by a low-affinity monoclonal anti-methamphetamine antibody.

Animals were trained to discriminate 5 or 10 mg/kg cocaine (rats), or 3 mg/kg (+)-amphetamine (pigeons) from saline, after which dose-response curves were determined for (+)-methamphetamine and other drugs before and after administration of a (+)-methamphetamine-specific monoclonal antibody (K(D) =250 nM). In rats trained to discriminate 10 mg/kg cocaine from saline, intravenous (+)-methamphetamine was about three times more potent as a discriminative stimulus than intraperitoneal (+)-methamphetamine. Also in these rats, intraperitoneal (+)-methamphetamine and (+)-amphetamine were about equipotent as discriminative stimuli, and were about three times more potent than intraperitoneal cocaine. In pigeons trained to discriminate 3 mg/kg intramuscular (i.m.) (+)-amphetamine from saline, (+)-methamphetamine and (+)-amphetamine were nearly equipotent, while cocaine was slightly less potent. In rats trained to discriminate 5 or 10 mg/kg cocaine from saline, intravenous administration of 1 g/kg of the antibody shifted both intravenous and intraperitoneal dose-response curves for (+)-methamphetamine discrimination approximately threefold to the right at 1 or 4 days after administration of the antibody. In pigeons trained to discriminate 3 mg/kg intramuscular (+)-amphetamine from saline, a similar shift of the (+)-methamphetamine dose-response curve to the right also lasted for 4-7 days. However, the antibody did not affect the (+)-amphetamine dose-response curve (pigeons), or the cocaine (rats) dose-response curve. The data show that a low affinity anti-(+)-methamphetamine-specific antibody can produce a specific antagonism of an effect of (+)-methamphetamine that is closely associated with its abuse.

Animals↗

PubMed2002

Drug discrimination under concurrent variable-ratio variable-ratio schedules.

Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under concurrent variable-ratio (VR) VR schedules, in which responses on the pentobarbital-biased lever were reinforced under the VR schedule with the smaller response requirements when pentobarbital was given before the session, and responses on the saline-biased key were reinforced under the VR schedule with the larger response requirements. When saline was administered before the session, the reinforcement contingencies associated with the two response keys were reversed. When responding stabilized under concurrent VR 20 VR 30, concurrent VR 10 VR 40, or concurrent VR 5 VR 50 schedules, pigeons responded almost exclusively on the key on which fewer responses were required to produce the reinforcer. When other doses of pentobarbital and other drugs were substituted for the training dose, low doses of all drugs produced responding on the saline-biased key. Higher doses of pentobarbital and chlordiazepoxide produced responding only on the pentobarbital-biased key, whereas higher doses of ethanol and phencyclidine produced responding only on this key less often. d-Amphetamine produced responding primarily on the saline-biased key. When drugs generalized to pentobarbital, the shape of the generalization curve under concurrent VR VR schedules was more often graded than quantal in shape. Thus, drug discrimination can be established under concurrent VR VR schedules, but the shapes of drug-discrimination dose-response curves under concurrent VR VR schedules more closely resemble those seen under interval schedules than those seen under fixed-ratio schedules. Graded dose-response curves under concurrent VR VR schedules may relate to probability matching and difficulty in discriminating differences in reinforcement frequency.

Animals↗