Regional Restriction of Alcohol/Retinol Dehydrogenases along the Mouse Gastrointestinal Epithelium

Abstract

The gastrointestinal tract is a major site of alcohol dehydrogenase (ADH) activity in humans and rodents. Because class I ADH (ADH-I) and class IV ADH (ADH-IV), but not class III ADH (ADH-III), function as retinol dehydrogenases in vitro and may thus participate in retinoid signaling needed for epithelial differentiation, the aim of this study was to determine the localization of these enzymes along the gastrointestinal tract. Specific antibodies were used to examine the tissue distribution of all three known classes of mouse ADH by Western blotting, and cellular localization was determined by immunohistochemistry. ADH-I was detected primarily in the intestine, liver, kidney, adrenal, and uterus, with detection of ADH-III in all tissues examined, and detection of ADH-IV primarily in the esophagus, stomach, adrenal, skin, ovary, and epididymis. Along the gastrointestinal tract, ADH-III was not specifically localized, whereas ADH-I was localized exclusively in the villus epithelium of the small intestine and absorptive epithelium of the large intestine, with ADH-IV being localized exclusively in the basal and suprabasal epithelial cells of the esophagus and gastric pit surface epithelium of the stomach. The ADH localization patterns observed are consistent with ADH-I and ADH-IV, but not ADH-III, functioning physiologically in retinol metabolism needed for epithelial differentiation. Our results further suggest that the functions of ADH-I and ADH-IV are regionally restricted to the lower and upper components, respectively, of the gastrointestinal epithelium, a finding that may relate to the different efficiencies of these two enzymes for retinol oxidation, as well as to the different susceptibilities of the upper and lower digestive tracts for ethanol-induced cancers.

Distinct Retinoid Metabolic Functions for Alcohol Dehydrogenase Genes Adh1 and Adh4 in Protection against Vitamin A Toxicity or Deficiency Revealed in Double Null Mutant Mice

“…As mammalian ADH1 and ADH4 each have high activity for oxidation of retinol to retinal (ADH1 activity reported as 30 -300 nmol/min/ mg; ADH4 activity reported as 110 -1675 nmol/min/mg) (16 -19), the lack of a major contribution by ADH4 in vivo is not due to lower retinol activity. However, it is consistent with the fact that ADH4 protein is not produced in mouse liver where a large amount of retinol metabolism is expected to occur (37).…”

“…Adh1 Ϫ/Ϫ mice exhibit a 10-fold decrease in metabolism of retinol to RA in liver. This correlates with liver being the tissue where ADH1 protein is most highly expressed in the adult mouse (37). In contrast, Adh4 Ϫ/Ϫ mice have a small decrease in conversion of retinol to RA in liver that is not statistically significant.…”

“…Other mice used in this study are the original Adh1 Ϫ/Ϫ and Adh4 Ϫ/Ϫ null mutant lines previously described (27,28) both of which have the same genetic background as the Adh1/4 and wild-type mice described here. For verification of a null mutant phenotype, polyclonal antibodies against mouse ADH1 and ADH4 were used to probe Western blots of mouse liver and stomach using 20 g of total protein per lane as reported (37).…”

Two Zebrafish Alcohol Dehydrogenases Share Common Ancestry with Mammalian Class I, II, IV, and V Alcohol Dehydrogenase Genes but Have Distinct Functional Characteristics

“…The highest level of ADH8A expression was in the liver, whereas the lowest levels measured were in the adult caudal fin. ADH8B was moderately expressed in a pattern similar to the ubiquitous expression of class III ADHs in other organisms (31). DISCUSSION It has been known since 1971 that ethanol causes developmental effects in zebrafish (10).…”

“…The medium-chain class III alcohol dehydrogenase in Drosophila melanogaster is expressed throughout the larval, pupal, and adult life stages of the fly (33). In mice, ADH5 mRNA is detected as early as 6.5 days postcoitum and is nearly ubiquitously expressed in adult tissues (31). ADH1s, on the other hand, have a more restricted tissue-specific expression pattern in the embryo and in adults.…”