Analysis of Phospholipid Hydroperoxide Glutathione Peroxidase mRNA

Phospholipid hydroperoxide glutathione peroxidase (PHGPX or GPX4, E.C. 1.11.1.12) is one of the four identified selenium-dependent glutathione peroxidases (GPX) in mammals (
1
). Both of the pig (2.8 kb) and the mouse (4.0 kb) GPX4 genes contain seven exons and six introns, with putative regulatory elements or binding sites for transcriptional factors (
2
,
3
). There is 95% homology among amino acid sequences deduced from the GPX4 c
DNA
of rat (
4
), mouse (
5
) and human (
6
). In contrast, the homology between GPX1 and GPX4 is less than 40%. There are two forms of GPX4: the long form (23 kDa) with a leader sequence for transportation to mitochondria, and the short form (20 kDa) or the non-mitochondrial form (
7
). Although GPX4 was initially considered mainly an antioxidant enzyme by reducing phospholipid hydroperoxides (
8
), it may be involved in sperm maturation (
9
) as there are abundant GPX4 activity and mRNA in testis (
10
,
11
) and rat epididymal spermatozoa (
12
). It exists as a soluble peroxidase in spermatids, but loses its activity in mature spermatozoa and persists as an oxidatively cross-linked insoluble protein (
13
). Besides, GPX4 is expressed in all major tissues studied so far. Comparatively, GPX4 mRNA and activity are less affected by changes in tissue selenium status than those of GPX1 or GPX3 (
14
). Because there is a selenium-independent enzyme that reduces phospholipid hydroperoxides (
15
), GPX4 mRNA analysis becomes a specific tool to distinguish these two enzymes for various biochemical and physiological studies.