Mechanical stress promotes the expression of smooth muscle-like properties in marrow stromal cells.
OBJECTIVE
It is poorly understood what kind of factors are involved in lineage commitment and maturation of mesenchymal stem cells. The present study investigates whether mechanical stress promotes expression of smooth muscle cell (SMC)-specific cytoskeletal protein in marrow stromal cells.


METHODS
Fibroblast-like stromal cells expressing STRO-1 antigen were isolated from rat bone marrow by density gradient separation. After preincubation for 7, 14, or 21 days in static condition, cells were exposed to one of three types of fluid flow-induced mechanical forces (flow dominant, pressure dominant, or combined) for 36 hours. The expression of SMC-specific cytoskeletal protein [alpha smooth muscle actin (alphaSMA) and smooth muscle myosin heavy chain (SMMHC)] was evaluated by immunofluorescence staining and Western blotting.


RESULTS
The proportion of SMMHC-positive cells was increased with longer preincubation periods (p < 0.01 vs 7-day incubation) and by any types of mechanical stimulation (p < 0.01 vs static control condition). The SMMHC-positive fraction after exposure to pressure-dominant forces (0.9% +/- 0.2%, 2.9% +/- 0.9%, and 12.6% +/- 0.8% for 7, 14, and 21 days of preincubation) or to combined forces (1.2% +/- 0.2%, 3.1% +/- 1.6%, and 15.5% +/- 2.8%) was higher than after flow-dominant stimulation (0, 1.2% +/- 0.1%, and 7.2% +/- 2.0%) (p < 0.01). In Western blotting, pressure-dominant or combined stimulation upregulated alphaSMA and SMMHC expression compared to static control condition.


CONCLUSIONS
The long-term cell incubation and subsequent mechanical stimulation, especially compressive strain, promote expression of SMC-specific cytoskeletal protein in marrow stromal cells.
Kobayashi
Nobuhiko
N
Department of Comprehensive Medicine 1, Jichi Medical School Omiya Medical Center, Saitama, Japan. nokobaya@ucsd.edu
Yasu
Takanori
T
Ueba
Hiroto
H
Sata
Masataka
M
Hashimoto
Shigemasa
S
Kuroki
Masatoshi
M
Saito
Muneyasu
M
Kawakami
Masanobu
M
D000199:Actins / Q000096:biosynthesis*; D000818:Animals; D000954:Antigens, Surface; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology* / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D019070:Cell Lineage / Q000502:physiology; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D013314:Stress, Mechanical; D017154:Stromal Cells / Q000166:cytology / Q000378:metabolism*
D000199:Actins; D000954:Antigens, Surface; C527498:STRO-1 antigen, rat; D018995:Myosin Heavy Chains