Renal pathology resulting from PGHS-2 gene ablation in DBA/B6 mice
Introduction
Prostaglandin H synthase (PGHS, cyclooxygenase, COX), a key enzyme in the production of prostanoids, exists as two isoforms: PGHS-1 and -2. Both of the isoforms convert arachidonic acid to prostaglandin H2 by a two-step reaction. Prostaglandin H2 is the substrate for many other synthases and epimerases that generate various prostaglandins and thromboxanes. Although both PGHS enzymes catalyze the same reaction, their biological roles are different. While PGHS-1 is constitutively expressed in many tissues, PGHS-2 is mainly a transient enzyme induced by inflammatory cytokines, growth factors, and tumor promoters [1], [2]. Both forms of PGHS are targets of nonsteroidal anti-inflammatory drugs (NSAIDs). However, greater emphasis has been placed on designing NSAIDs that specifically block PGHS-2 because of more frequent association of its expression with pathological conditions.
To more clearly determine the separate biological roles of PGHS-1 and -2, targeted disruption of PGHS-1 and -2 genes in mice was undertaken in two different laboratories [3], [4], [5]. As a result of studies in knock out mice unique roles of PGHS-1 and -2 were revealed, including the involvement of PGHS-2 in kidney development.
A role for PGHS in kidney development had already been inferred from reports linking renal abnormalities (ranging from oliguria to renal dysgenesis) of newborns with NSAID treatment of pregnant women [6], [7]. Supporting data also came from rhesus monkeys who had similar abnormalities after their mothers were treated with indomethacin during pregnancy [8]. In vitro data [9] reported that PGE1 was necessary for maximal growth of embryonic kidneys in culture. A number of recent studies have been directed to assess the unique contributions of the two PGHS isozymes in PGHS-1 [3] and PGHS-2 [4], [5] null mice.
While PGHS-1 null mice showed normal kidney development [3], the PGHS-2 null mice were born with renal abnormalities that included hypoplastic glomeruli, focal segmental and global glomerular sclerosis and interstitial fibrosis [4], [5], [10]. Chronic renal failure in PGHS-2 null mice led to increased rate of death [4], [5]. It was originally reported that the average life span of a PGHS-2 null mouse was about 3 months and only a few mice lived longer than 6 months [5]. Subsequently, Langenbach et al. [11] reported that 75% of the PGHS-2 null mice lived to at least 12 months of age. The variable life span seen in the two colonies of mice appears to be strain-dependent. Thus, in the C57Bl/6 (B6) background the lack of PGHS-2 leads to high rate of mortality soon after birth (Morham SG, personal communication). When the PGHS-2 null genotype is in a mixed 129 Ola/C57Bl/6J background, the animals live longer [11]. We show here that PGHS-2 null mice with a mixed genetic background (DBA/B6) do not suffer from high rates of death as a result of less severe renal abnormalities.
Section snippets
Animals
Wild type (WT) and PGHS-2 null (PGHS-2−/−) mice in a mixed DBA/B6 background were bred and genotyped as previously reported [12]. Mice were maintained in micro-isolator cages on 8460 22/5 rodent diet (w) (≥22% protein, 0.4% Na, 0.67% Cl) (Harlan Teklad, Madison, WI) and tap water, available ad libitum.
Plasma chemistries
Blood was collected from all animals once every 2 weeks, starting at 8 weeks of age and continuing to 33 weeks of age. After anesthetizing each mouse by inhalation of methoxyflurane (Abbot
Survival
The average number of pups born from mating between PGHS-2−/− sires and PGHS-2−/+ dams in our colony was seven and this was similar to the average number of pups born to wild type DBA/B6 parents. A difference in survival between the two types of litters was revealed at weaning (3–4 weeks postnatal). In wild type litters 92% of the pups survived to weaning, while only 66% of pups from PGHS-2 litters survived. Based on the prediction of Mendelian ratio of inherited traits, PGHS-2−/− pups
Discussion
Careful analyses of kidneys from transgenic mice lacking PGHS-2 [4], [5], [10] or from normal mice treated with PGHS-2-specific inhibitor [13] reveal that PGHS-2 is essential for optimal renal development and function. However, the absence of PGHS-2 from the kidney appears to have variable impact depending on the genetic background of the mouse. This observation is similar to what has been described in a number of other mutant or knockout mice whose phenotypes are modified by their genetic
Acknowledgements
This work was supported by research funds from the Office of Research and Development, Medical Research Service, Department of Veterans Affairs (R.R) and from the National Kidney Foundation, West Tennessee Chapter (S.J.F.L.). The authors would like to thank Sarita Goorha for her valuable help in maintaining the colony of PGHS-null mice, Therese Mangold for performing analysis of the blood samples, Angela Williams for preparing the histological sections, Mary Alice Bobal and Amina Fu for
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