ISX is a retinoic acid-sensitive gatekeeper that controls intestinal beta,beta-carotene absorption and vitamin A production.
The uptake of dietary lipids from the small intestine is a complex process that depends on the activities of specific membrane receptors with yet unknown regulatory mechanisms. Using both mouse models and human cell lines, we show here that intestinal lipid absorption by the scavenger receptor class B type 1 (SR-BI) is subject to control by retinoid signaling. Retinoic acid via retinoic acid receptors induced expression of the intestinal transcription factor ISX. ISX then repressed the expression of SR-B1 and the carotenoid-15,15'-oxygenase Bcmo1. BCMO1 acts downstream of SR-BI and converts absorbed beta,beta-carotene to the retinoic acid precursor, retinaldehyde. Using BCMO1-knockout mice, we demonstrated increased intestinal SR-BI expression and systemic beta,beta-carotene accumulation. SR-BI-dependent accumulation of beta,beta-carotene was prevented by dietary retinoids that induced ISX expression. Thus, our study revealed a diet-responsive regulatory network that controls beta,beta-carotene absorption and vitamin A production by negative feedback regulation. The role of SR-BI in the intestinal absorption of other dietary lipids, including cholesterol, fatty acids, and tocopherols, implicates retinoid signaling in the regulation of lipid absorption more generally and has clinical implications for diseases associated with dyslipidemia.
Lobo
Glenn P
GP
Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44160, USA.
Hessel
Susanne
S
Eichinger
Anne
A
Noy
Noa
N
Moise
Alexander R
AR
Wyss
Adrian
A
Palczewski
Krzysztof
K
von Lintig
Johannes
J
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D003106:Colon / Q000166:cytology / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051122:Scavenger Receptors, Class B / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014801:Vitamin A / Q000378:metabolism*; D019207:beta Carotene / Q000378:metabolism*; D050559:beta-Carotene 15,15'-Monooxygenase / Q000502:physiology*
C527930:Isx protein, mouse; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D014157:Transcription Factors; D019207:beta Carotene; D014801:Vitamin A; C493359:Bco1 protein, mouse; D050559:beta-Carotene 15,15'-Monooxygenase