Attenuation of UVR-induced vitamin D3synthesis in a mouse model deleted for keratinocyte lathosterol 5-desaturase.
The lower risk of some internal cancers at lower latitudes has been linked to greater sun exposure and consequent higher levels of ultraviolet radiation (UVR)-produced vitamin D3(D3). To separate the experimental effects of sunlight and of all forms of D3, a mouse in which UVR does not produce D3would be useful. To this end we have generated mice carrying a modified allele of sterol C5-desaturase (Sc5d), the gene encoding the enzyme that converts lathosterol to 7-dehydrocholesterol (7-DHC), such that Sc5d expression can be inactivated using the Cre/lox site-specific recombination system. By crossing to mice with tissue-specific expression of Cre or CreER2(Cre/estrogen receptor), we generated two lines of transgenic mice. One line has constitutive keratinocyte-specific inactivation of Sc5d (Sc5dk14KO). The other line (Sc5dk14KOi) has tamoxifen-inducible keratinocyte-specific inactivation of Sc5d. Mice deleted for keratinocyte Sc5d lose the ability to increase circulating D3following UVR exposure of the skin. Thus, unlike in control mice, acute UVR exposure did not affect circulating D3level in inducible Sc5dk14KOimice. Keratinocyte-specific inactivation of Sc5d was proven by sterol measurement in hair - in control animals lathosterol and cholesta-7,24-dien-3β-ol, the target molecules of SC5D in the sterol biosynthetic pathways, together constituted a mean of 10% of total sterols; in the conditional knockout mice these sterols constituted a mean of 56% of total sterols. The constitutive knockout mice had an even greater increase, with lathosterol and cholesta-7,24-dien-3β-ol accounting for 80% of total sterols. In conclusion, the dominant presence of the 7-DHC precursors in hair of conditional animals and the lack of increased circulating D3following exposure to UVR reflect attenuated production of the D3photochemical precursor 7-DHC and, consequently, of D3itself. These animals provide a useful new tool for investigating the role of D3in UVR-induced physiological effects and, more broadly, for investigations of the cholesterol synthetic pathway in the skin and other targeted tissues.
UCSF Benioff Children's Hospital Oakland Research Institute (CHORI), Oakland, CA, USA.
Anastasia M
AM
Makarova
UCSF Benioff Children's Hospital Oakland Research Institute (CHORI), Oakland, CA, USA.
Saloni
S
Pasta
UCSF Benioff Children's Hospital Oakland Research Institute (CHORI), Oakland, CA, USA.
Gordon
G
Watson
UCSF Benioff Children's Hospital Oakland Research Institute (CHORI), Oakland, CA, USA; Institute of Metabolism and Systems Research (IMSR), College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Cedric
C
Shackleton
UCSF Benioff Children's Hospital Oakland Research Institute (CHORI), Oakland, CA, USA. Electronic address: eepstein@chori.org.
Ervin H
EH
Epstein
D000818:Animals; D002762:Cholecalciferol / Q000096:biosynthesis / Q000097:blood*; D002784:Cholesterol / Q000378:metabolism; D003433:Crosses, Genetic; D003684:Dehydrocholesterols / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D006197:Hair / Q000378:metabolism; D006579:Heterozygote; D053208:Kaplan-Meier Estimate; D015603:Keratinocytes / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D008297:Male; D008661:Metabolism, Inborn Errors / Q000097:blood / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D011247:Pregnancy; D011897:Random Allocation; D012867:Skin / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D014466:Ultraviolet Rays
D003684:Dehydrocholesterols; C033144:lathosterol delta-5-dehydrogenase; D002762:Cholecalciferol; C002402:cholesta-7,9-dien-3-beta-ol; C001521:lathosterol; D002784:Cholesterol; D044925:Oxidoreductases Acting on CH-CH Group Donors
Cre activation; Hair sterols; Lathosterol; Sc5d knockout; Sterol C5-desaturase (Sc5d); Sterol analysis; Vitamin D(3) synthesis