Expression of the cathelicidin LL-37 is modulated by short chain fatty acids in colonocytes: relevance of signalling pathways.
OBJECTIVE
Short chain fatty acids (SCFA) exert profound effects on the colonic mucosa. In particular, SCFA modulate mucosal immune functions. The antimicrobial cathelicidin LL-37 is expressed by colon epithelial cells. In the present study the effect of SCFA on LL-37 expression was investigated.


METHODS
LL-37 expression in vivo was assessed by immunohistochemistry. Real time quantitative reverse transcription-polymerase chain reaction was employed to determine LL-37 expression in colonocytes in vitro after treatment with various cytokines, SCFA, or flavone. LL-37 levels were correlated to cell differentiation which was determined by alkaline phosphatase (AP) activity. In addition, intracellular signalling pathways such as MEK-ERK (mitogen/extracellular signal protein kinase (MEK)/extracellular signal regulated protein kinase (ERK)) and p38/mitogen activated protein (MAP) kinase were explored.


RESULTS
In vivo, LL-37 expression in healthy mucosa was restricted to differentiated epithelial cells in human colon and ileum. In colonocytes, increased LL-37 expression associated with cell differentiation was detected in vitro following treatment with butyrate, isobutyrate, propionate, and trichostatin A. Flavone induced LL-37 transcription but did not affect AP activity while cytokines had no effect. To dissect pathways mediating differentiation and LL-37 expression, specific inhibitors were applied. Inhibition of the protein kinase MEK enhanced butyrate induced AP activity while LL-37 expression in colon epithelial cells was blocked. In contrast, inhibition of p38/MAP kinase blocked cell differentiation without inhibiting LL-37 expression.


CONCLUSIONS
Expression of the cathelicidin LL-37 in colonocytes and cellular differentiation are separately modulated by SCFA via distinct signalling pathways. These data may provide a rationale for dietary modulation of mucosal defence mechanisms.
Schauber
J
J
Department of Medicine, Division of Gastroenterology, University of Würzburg, Germany. j.schauber@medizin.uni-wuerzburg.de
Svanholm
C
C
Termén
S
S
Iffland
K
K
Menzel
T
T
Scheppach
W
W
Melcher
R
R
Agerberth
B
B
Lührs
H
H
Gudmundsson
G H
GH
D000328:Adult; D000469:Alkaline Phosphatase / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects; D001706:Biopsy; D002087:Butyrates / Q000494:pharmacology; D054804:Cathelicidins; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D003106:Colon / Q000166:cytology / Q000187:drug effects*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000494:pharmacology*; D047309:Flavones; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007150:Immunohistochemistry / Q000379:methods; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000502:physiology*
D023181:Antimicrobial Cationic Peptides; D002087:Butyrates; D054804:Cathelicidins; D005232:Fatty Acids, Volatile; D047309:Flavones; D005419:Flavonoids; D006877:Hydroxamic Acids; D011500:Protein Synthesis Inhibitors; C012589:trichostatin A; D011494:Protein Kinases; D000469:Alkaline Phosphatase; C043562:flavone