Cellular retinol-binding protein I is essential for vitamin A homeostasis

Abstract

C.Båvik and V.Sapin contributed equally to this workThe gene encoding cellular retinol (ROL, vitA)-binding protein type I (CRBPI) has been inactivated. Mutant mice fed a vitA-enriched diet are healthy and fertile. They do not present any of the congenital abnormalities related to retinoic acid (RA) deficiency, indicating that CRBPI is not indispensable for RA synthesis. However, CRBPI deficiency results in an~50% reduction of retinyl ester (RE) accumulation in hepatic stellate cells. This reduction is due to a decreased synthesis and a 6-fold faster turnover, which are not related to changes in the levels of RE metabolizing enzymes, but probably reflect an impaired delivery of ROL to lecithin:retinol acyltransferase. CRBPI-null mice fed a vitA-deficient diet for 5 months fully exhaust their RE stores. Thus, CRBPI is indispensable for efficient RE synthesis and storage, and its absence results in a waste of ROL that is asymptomatic in vitA-sufficient animals, but leads to a severe syndrome of vitA deficiency in animals fed a vitA-deficient diet.

HPLC/UV quantitation of retinal, retinol, and retinyl esters in serum and tissues

“…Liver RE in mice fed a 4IU vitamin A/g diet was 562 nmol/g, which was comparable to or lower than RE values reported with a stock diet (473-5500 nmol/g) (16,17,22-25,31,32,44,48). Previous stock diet adipose and liver RAL values were 0.15-0.8 nmol/g and 0.9 nmol/g, respectively, 2-to 6-fold higher than adipose (0.064 nmol/g) and liver (0.161 nmol/g) values obtained from mice fed a 4IU vitamin A/g diet (17,36).…”

“…RA exerts additional biological effects through dimerization of RXR with an array of other type II nuclear receptors (13). Various approaches have been used to determine effectors of retinoid metabolism, such as genetic alteration of retinoid-binding proteins (16)(17)(18)(19)(20)(21), enzymes (22)(23)(24)(25), and receptors (12,13,26), dietary manipulation of vitamin A intake (28), and exposure to xenobiotics (29)(30)(31)(32). Quantifying how manipulation of retinoid metabolism effects the flux of retinoids through metabolic paths and/or effects availability of substrate for RA production will provide insight into retinoid homeostasis and metabolism, and thereby function.…”

Retinoids and spermatogenesis: Lessons from mutant mice lacking the plasma retinol binding protein

“…Accordingly, the testes of Rbp4-null mice did not display histological abnormalities, at 6 weeks ( Fig. 2E,F) and 1 year of age (not shown), notably defects related to an impaired RA signalling (Lufkin et al, 1993;Ghyselinck et al, 1999). These data indicate that RBP deficiency decreases testis ROL stores.…”

“…In addition to the retina, the testis is highly sensitive to VAD in mammals and in other vertebrate species (Wolbach and Howe, 1925;Howell et al, 1963;Hall et al, 1980;Ghyselinck et al, 1999). In the extensively studied vitamin A-deficient rat model, meiotic and post-meiotic germ cells vanish within 1 to 2 weeks following the disappearance of circulating ROL, yielding tubules containing Sertoli cells, preleptotene spermatocytes, and type A spermatogonia Sobhon et al, 1979;Huang et al, 1988;van Pelt and de Rooij, 1990b;de Rooij et al, 1994;Morales and Cavicchia, 2002; and references therein).…”

“…Absorbance was monitored at 325 nm. Compound identity and quantification were deduced from retention times and integrated peak areas, respectively (see Ghyselinck et al, 1999). Using this procedure, the detection limits were 1 ng/g (ϳ4 nmol/g) of tissue for ROL and 1 ng/g (ϳ2 nmol/g) of tissue for RP.…”