Ph.D., Johns Hopkins University, 1984
Associate Professor
Department of Molecular Pharmacology,
Physiology & Biotechnology
316 Biomedical Center
Tel. (401) 863-3288
Fax. (401) 863-1222
Email: Chi-Ming_Hai@brown.edu

Research Summary

Our research is concerned with how mechanical force and deformation modulate airway smooth muscle responsiveness and remodeling. We take an integrative approach to this research area by performing experiments from muscle mechanics to gene expression.

The incidence of asthma is increasing rapidly every year in the U.S., but the underlying mechanism is not fully understood. It is known that hyperresponsiveness of airway smooth muscle cells causes airway constriction and asthmatic symptoms, but the basic physiology of airway smooth muscle is not fully understood.

Recent findings indicate that periodic deep inspirations may be important in keeping the airways in the open state in normal subjects. When normal subjects were asked to withhold deep inspirations such as yawning and signing, these subjects developed asthmatic symptoms. When these subjects were allowed to resume deep inspirations, their airways open up and their asthmatic symptoms disappeared. In contrast, when asthmatic patients were asked to take deep inspirations, their asthma symptoms worsened. These findings suggest that asthmatic and normal airways may be fundamentally different in their responses to deep inspiration. These findings also suggest that mechanical force and/or deformation modulate contractility and/or structure of airway smooth muscle cells.

Overview of Our Research

We are interested in understanding how mechanical force and/or deformation (stress/strain) modulate the following processes in airway smooth muscle: a) membrane signal transduction, b) intracellular [Ca²⁺] regulation, c) cytoskeletal (CSK) filament and dense plaque (DP) organization, d) crossbridge (CB) cycling, and e) contractile protein and gene expression. These processes are summarized in the following diagram.

Intracellular [Ca2+] and Ca2+ Influx: We test the hypothesis that mechanical stress/strain modulates intracellular [Ca2+] in airway smooth muscle cells by modulating Ca2+ influx. Intracellular [Ca2+] is measured using the photoprotein, aequorin. Photons emitted by aequorin are measured by computer-based photon-counting system. Ca2+ influx is measured using radioactive 45Ca.

Cytoskeletal Recruitment of Vinculin: Vinculin is the critical protein in the assembly of focal adhesions (dense plaques). We hypothesize that mechanical strain/stress modulates cytoskeletal structure by modulating recruitment of vinculin to the actin cytoskeleton. Cytoskeletal fractions are isolated by ultracentrifugation of smooth muscle homogenate. Vinculin is separated from other proteins by SDS-polyacrylamide gel electrophoresis, and detected by immunoblotting.

Contractile and Cytoskeletal Protein and Gene Expression: Smooth muscle contractility is ultimately determined by the amount of contractile and cytoskeletal filaments. We test the hypothesis that mechanical stress/strain modulates gene and protein expression of contractile and cytoskeletal proteins via the MAP kinase pathways and/or secretion of autocrines. Protein expression is detected using SDS-polyacrylamide gel electrophoresis. Gene expression is detected using reverse transcription-polymerase chain reaction (RT-PCR).

Phospholipase C Translocation: Phospholipase C is the key signal transduction enzyme in the production of the two intracellular messengers, IP3 and diacylglycerol. We test the hypothesis that mechanical stress/strain modulates the translocation of phospholipase C from cytoplasm to the cell membrane. Phospholipase C distribution in single smooth muscle cells is detected using immunofluorescence labeling and fluorescence microscopy. Cytosolic and membrane fractions are separated by ultracentrifugation of smooth muscle homogenate. Phospholipase C in the two fractions are separated from other proteins by SDS-polyacrylamide gel electrophoresis. Phospholipase C is detected using immunoblotting.

Muscle Mechanics: We hypothesize that mechanical stress/strain induces adaptive changes in muscle mechanics such as isometric force, stiffness, and shortening velocity by cytoskeletal reorganization. These mechanical parameters are measured using a computer-based lever system and isometric force transducers. Cytoskeletal reorganization is controlled using pharmacologic agents.

Immunosensitization of Airway Smooth Muscle: This project is still at the planning stage. We hypothesize that passive immunosensitization modulates mechanosensitivity of airway smooth muscle. Passive immunosensitization is induced by treating airway smooth muscle with immune serum. Mechanosensitivity of airway smooth muscle is determined by measuring the length-dependencies of intracellular [Ca2+] and myosin light chain phosphorylation.

Chan, Wah-Lun, J. Silberstein, and Chi-Ming Hai. Mechanical strain memory in airway smooth muscle. Am. J. Physiol: Cell. 278, 2000 (In Press).

An, Steven S. and Chi-Ming Hai. Mechanical strain modulates maximal phosphatidylinositol turnover in airway smooth muscle. Am. J. Physiol., 277: L968-L974, 1999.

Wong, Chun Tung and Chi-Ming Hai. Mucosal modulation of agonist-induced myosin phosphorylation and contraction in airway smooth muscle. Respiration Physiology, 115: 103-111, 1999.

Youn, Thomas, Son A Kim, and Chi-Ming Hai. Length-dependent modulation of smooth muscle activation: effects of agonist, cytochalasin, and temperature. Am. J. Physiol. 274: C1601-C1607, 1998.

Tseng, S., R. Kim, T. Kim, K.G. Morgan, and C.-M. Hai. F-actin disruption attenuates agonist-induced [Ca²⁺], myosin phosphorylation, and force in smooth muscle. Am. J. Physiol. 272 (Cell Physiol. 41): C1960-C1967, 1997.

Szeto, B. and C.-M. Hai. Length-dependent modulation of myosin phosphorylation and contractile force in coronary arterial smooth muscle. Arch. Biochem. Biophys. 329: 241-248, 1996.

Yoo, J., R. Ellis, K.G. Morgan, and C.-M. Hai. Mechanosensitive modulation of myosin phosphorylation and phosphatidylinositol turnover in smooth muscle. Am. J. Physiol. 267 (Cell Physiol. 36): C1657-C1665, 1994