Colon OCTN2 gene expression is up-regulated by peroxisome proliferator-activated receptor gamma in humans and mice and contributes to local and systemic carnitine homeostasis.
In the large intestine organic cation transporter type-2 (OCTN2) is recognized as a transporter of compounds such as carnitine and colony sporulation factor, promoting health of the colon intestinal epithelium. Recent reports suggest that OCTN2 expression in small intestine is under control of peroxisome proliferator-activated receptor-alpha (PPARalpha). However, PPARalpha contribution to colonic OCTN2 expression remains controversial. Here we examined the transcriptional regulation of colon OCTN2 gene by PPARgamma. To exclude any additional modulation of other PPAR to OCTN2 expression, we used both in vivo and in vitro PPAR-null models and specific PPAR inhibitors. The PPARgamma agonists thiazolidinediones increased both OCTN2 mRNA and protein expression in colonic epithelial cell lines independently by PPARalpha expression. The induction was blocked only by PPARgamma antagonists or by gammaORF4, a PPARgamma isoform with dominant negative activity, suggesting a PPARgamma-dependent mechanism. A conserved noncanonical PPAR-responsive element was found by computational analysis in the first intron of human OCTN2 gene and validated by EMSA assay. Promoter-reporter assays further confirmed transcriptional functionality of the putative PPAR response element, whereas selective mutation caused complete loss of responsiveness to PPARgamma activation. Finally, adenovirus-mediated overexpression of constitutively active PPARgamma mutant increased colon OCTN2 expression in PPARalpha(-/-) mice. Interestingly, animals overexpressing colon PPARgamma showed a significant increase in plasma carnitine, thus demonstrating the functional contribution of large intestine to systemic carnitine homeostasis. This study reveals a PPARgamma-dependent absorption machinery in colon that is likely involved in the health of colon epithelium, in the microbiota-host interactions and in the absorption of nutraceuticals and drugs.
D'Argenio
Giuseppe
G
Gastroenterologia, Dipartimento di Medicina Clinica e Sperimentale, Federico II University, 80131 Naples, Italy.
Petillo
Orsolina
O
Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy.
Margarucci
Sabrina
S
Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy.
Torpedine
Angela
A
Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy.
Calarco
Anna
A
Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy.
Koverech
Angela
A
Facoltà di Medicina, La Sapienza 2, 00185 Roma, Italy.
Boccia
Angelo
A
Dipartimento di Biochimica e Biotecnologie Mediche, Federico II University, CEINGE-Biotecnologie Avanzate, 80131 Naples, Italy.
Paolella
Giovanni
G
Dipartimento di Biochimica e Biotecnologie Mediche, Federico II University, CEINGE-Biotecnologie Avanzate, 80131 Naples, Italy.
Peluso
Gianfranco
G
Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Naples, Italy. Electronic address: g.peluso@ibp.cnr.it.
D000818:Animals; D002331:Carnitine / Q000235:genetics / Q000378:metabolism*; D002461:Cell Line, Transformed; D003106:Colon / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D007421:Intestine, Small / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009928:Organ Specificity / Q000502:physiology; D027701:Organic Cation Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D047493:PPAR alpha / Q000235:genetics / Q000378:metabolism; D047495:PPAR gamma / Q000819:agonists / Q000378:metabolism*; D020033:Protein Isoforms / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000502:physiology; D000074058:Solute Carrier Family 22 Member 5; D045162:Thiazolidinediones / Q000494:pharmacology
D007004:Hypoglycemic Agents; D027701:Organic Cation Transport Proteins; D047493:PPAR alpha; D047495:PPAR gamma; D020033:Protein Isoforms; C492020:SLC22A5 protein, human; C492019:Slc22a5 protein, mouse; D000074058:Solute Carrier Family 22 Member 5; D045162:Thiazolidinediones; C089946:2,4-thiazolidinedione; D002331:Carnitine