Renal concentrating defect in mice lacking group IV cytosolic phospholipase A₂

Abstract

Eicosanoids regulate various cellular functions that are important in physiological and pathophysiological processes. Arachidonic acid is released from membranes by phospholipase A(2) (PLA(2)) activity. Activated macrophages derived from mice lacking the 85-kDa group IV cytosolic PLA(2) (cPLA(2)) have a markedly reduced release of prostaglandin E(2) and leukotrienes B(4) and C(4). Under basal conditions and after furosemide, urinary prostaglandin E(2) excretion is reduced in cPLA(2)-knockout (cPLA(2)(-/-)) mice. Serum creatinine, Na(+), K(+), and Ca(2+) concentrations, glomerular filtration rate, and fractional excretion of Na(+) and K(+) are not different in cPLA(2)(-/-) and cPLA(2)(+/+) mice. Maximal urinary concentration is lower in 48-h water-deprived cPLA(2)(-/-) mice compared with cPLA(2)(+/+) animals (1,934 +/- 324 vs. 3,541 +/- 251 mmol/kgH(2)O). Plasma osmolality is higher (337 +/- 5 vs. 319 +/- 3 mmol/kgH(2)O) in cPLA(2)(-/-) mice that lose a greater percentage of their body weight (20 +/- 2 vs. 13 +/- 1%) compared with cPLA(2)(+/+) mice after water deprivation. Vasopressin does not correct the concentrating defect. There is progressive reduction in urinary osmolality with age in cPLA(2)(-/-) mice. Membrane-associated aquaporin-1 (AQP1) expression, identified by immunocytochemical techniques, is reduced markedly in proximal tubules of older cPLA(2)(-/-) animals but is normal in thin descending limbs. However, Western blot analysis of kidney cortical samples revealed an equivalent AQP1 signal intensity in cPLA(2)(+/+) and cPLA(2)(-/-) animals. Young cPLA(2)(-/-) mice have normal proximal tubule AQP1 staining. Collecting duct AQP2, -3, and -4 were normally expressed in the cPLA(2)(-/-) mice. Thus mice lacking cPLA(2) develop an age-related defect in renal concentration that may be related to abnormal trafficking and/or folding of AQP1 in the proximal tubule, implicating cPLA(2) in these processes.

20-HETE and Furosemide-Induced Natriuresis in Salt-Sensitive Essential Hypertension

“…The latter mechanism is important, as demonstrated by inhibition of vanadate-induced PGE 2 synthesis and chloride transport by PLA 2 antagonists in rabbit colon 27 and by the abolition of the PGE 2 response to furosemide in knockout mice that are Ϫ/Ϫ for a 85-kDa group IV cytosolic PLA 2 . 28 Therefore, there is no need to invoke an action of furosemide on CYP 450 monooxygenases to account for furosemide-induced stimulation of excretion of 20-HETE, as observed in our SR patients. Increased substrate availability by PLA 2 in response to furosemide could suffice to explain this finding.…”

Role of Microsomal Prostaglandin E Synthase 1 in the Kidney

“…Alternatively, the capacity of PGE 2 to influence vasopressin actions in vivo may be less robust than suggested by studies in cell culture or isolated perfused nephron segments (50,52). However, alterations in urinary concentrating capacity did not become apparent in cytosolic phospholipase A2 (cPLA2)-deficient mice until Ͼ320 d of age (24), and our studies were carried out in mice that were Ͻ6 mo of age.…”

“…Concentrations of PGEM in urine were determined by using a specific ELISA assay (Cayman Chemicals, Ann Arbor, MI). Previous studies have shown that urinary PGEM is a reliable indicator of urinary PGE 2 excretion in vivo (24). Thromboxane B 2 (TxB 2 ), the stable metabolite of TxA 2 , and 6-keto-PGF 1␣ , the stable metabolite of prostacyclin (PGI 2 ), were measured in fresh urine using specific ELISA (Cayman Chemicals).…”

Regulatory Mechanism and Physiological Role of Cytosolic Phospholipase A2

“…82) Aged cPLA 2 a-deficient mice have abnormality in urine concentrating ability because of reduced aquoporin-1 expression in proximal tubules. 83) Female pregnant mice with the null mutation for cPLA 2 a have difficulties in delivery, and need either cesarean section or administration of progesterone antagonists. 9) This phenotype is explained by the lack of prostaglandin F 2 a production, as a similar failure of delivery was also reported in FP (the receptor for prostaglandin F 2 a)-deficient mice.…”