Myosin light chain kinase is central to smooth muscle contraction and required for gastrointestinal motility in mice.
OBJECTIVE
Smooth muscle is essential for maintaining homeostasis for many body functions and provides adaptive responses to stresses imposed by pathologic disorders. Identified cell signaling networks have defined many potential mechanisms for initiating smooth muscle contraction with or without myosin regulatory light chain (RLC) phosphorylation by myosin light chain kinase (MLCK). We generated tamoxifen-inducible and smooth muscle-specific MLCK knockout (KO) mice and provide direct loss-of-function evidence that shows the primary importance of MLCK in phasic smooth muscle contractions.


METHODS
We used the Cre-loxP system to establish Mlck floxed mice in which exons 23, 24, and 25 were flanked by 2 loxP sites. Smooth muscle-specific MLCK KO mice were generated by crossing Mlck floxed mice with SM-CreER(T2) (ki) mice followed by tamoxifen treatment. The phenotype was assessed by histologic, biochemical, molecular, cell biological, and physiologic analyses.


RESULTS
Targeted deletion of MLCK in adult mouse smooth muscle resulted in severe gut dysmotility characterized by weak peristalsis, dilation of the digestive tract, and reduction of feces excretion and food intake. There was also abnormal urinary bladder function and lower blood pressure. Isolated muscles showed a loss of RLC phosphorylation and force development induced by K(+)-depolarization. The kinase knockout also markedly reduced RLC phosphorylation and force development with acetylcholine which activates Ca(2+)-sensitizing signaling pathways.


CONCLUSIONS
MLCK and its phosphorylation of RLC are required physiologically for smooth muscle contraction and are essential for normal gastrointestinal motility.
He
Wei-Qi
WQ
Model Animal Research Center and MOE Key Laboratory of Model Animal for Disease Study, Nanjing University, Nanjing, China.
Peng
Ya-Jing
YJ
Zhang
Wen-Cheng
WC
Lv
Ning
N
Tang
Jing
J
Chen
Chen
C
Zhang
Cheng-Hai
CH
Gao
Song
S
Chen
Hua-Qun
HQ
Zhi
Gang
G
Feil
Robert
R
Kamm
Kristine E
KE
Stull
James T
JT
Gao
Xiang
X
Zhu
Min-Sheng
MS
D000818:Animals; D001794:Blood Pressure; D002118:Calcium / Q000378:metabolism; D003672:Defecation; D004435:Eating; D005260:Female; D005769:Gastrointestinal Motility; D005838:Genotype; D007422:Intestines / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction; D053580:Muscle Strength; D009130:Muscle, Smooth / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000235:genetics / Q000378:metabolism*; D010528:Peristalsis; D010641:Phenotype; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D013997:Time Factors; D014161:Transduction, Genetic; D001743:Urinary Bladder / Q000503:physiopathology
D018994:Myosin Light Chains; D009219:Myosin-Light-Chain Kinase; D011188:Potassium; D002118:Calcium