Kidney-Specific CAP1/Prss8-Deficient Mice Maintain ENaC-Mediated Sodium Balance through an Aldosterone Independent Pathway

Abstract

The serine protease prostasin (CAP1/Prss8, channel-activating protease-1) is a confirmed in vitro and in vivo activator of the epithelial sodium channel ENaC. To test whether proteolytic activity or CAP1/Prss8 abundance itself are required for ENaC activation in the kidney, we studied animals either hetero- or homozygous mutant at serine 238 (S238A; Prss8cat/+ and Prss8cat/cat), and renal tubule-specific CAP1/Prss8 knockout (Prss8PaxLC1) mice. When exposed to varying Na+-containing diets, no changes in Na+ and K+ handling and only minor changes in the expression of Na+ and K+ transporting protein were found in both models. Similarly, the α- or γENaC subunit cleavage pattern did not differ from control mice. On standard and low Na+ diet, Prss8cat/+ and Prss8cat/cat mice exhibited standard plasma aldosterone levels and unchanged amiloride-sensitive rectal potential difference indicating adapted ENaC activity. Upon Na+ deprivation, mice lacking the renal CAP1/Prss8 expression (Prss8PaxLC1) exhibit significantly decreased plasma aldosterone and lower K+ levels but compensate by showing significantly higher plasma renin activity. Our data clearly demonstrated that the catalytic activity of CAP1/Prss8 is dispensable for proteolytic ENaC activation. CAP1/Prss8-deficiency uncoupled ENaC activation from its aldosterone dependence, but Na+ homeostasis is maintained through alternative pathways.

Role of epithelial sodium channel-related inflammation in human diseases

“…The ENaC is firstly found in the apical surface of epithelial cells ( 23 ). The αβγ channel is expressed in many organs, such as in the kidneys (distal convoluted tubule, connecting tubule, collecting duct) ( 24 ), skin (keratinocyte, sweat gland) ( 25 ), vascular system (endothelium, smooth muscle) ( 26 ), lungs (alveolar cell, airway cell) ( 27 ), colon ( 28 ), and tongue ( 29 ).The δENaC has also been found in many non-renal organs, such as in the ovaries, brain, liver, lungs, heart, and vessel ( 13 , 16 , 30 ) ( Figure 1 ).…”

Kidney-Specific Membrane-Bound Serine Proteases CAP1/Prss8 and CAP3/St14 Affect ENaC Subunit Abundances but Not Its Activity

“…The following genotype was analyzed for the CAP3/St14 knockout mice (Ko): St14 lox/lox ;Pax8rTA Tg/0 ;TRE-LC1 Tg/0 . Inducible nephron-specific CAP1/Prss8 and CAP3/St14 double knockout mice (DKo) were generated by intercrossing inducible nephronspecific single CAP1/Prss8 knockout mice [17] with inducible nephron-specific CAP3/St14 mice to obtain DKo: Prss8 lox/lox ; St14 lox/lox ; Pax8rTA Tg/0 ; TRE-LC1 Tg/0 . The following genotypes were obtained for the control mice: Prss8 lox/lox ;St14 lox/lox ;Pax8rTA Tg/0 ; TRE-LC1 0/0 or Prss8 lox/lox ; St14 lox/lox ; Pax8rTA 0/0 ; TRE-LC1 Tg/0 or, Prss8 lox/lox ; St14 lox/lox ; Pax8rTA 0/0 ; TRE-LC1 0/0 .…”

“…The following genotypes were obtained for the control mice: Prss8 lox/lox ;St14 lox/lox ;Pax8rTA Tg/0 ; TRE-LC1 0/0 or Prss8 lox/lox ; St14 lox/lox ; Pax8rTA 0/0 ; TRE-LC1 Tg/0 or, Prss8 lox/lox ; St14 lox/lox ; Pax8rTA 0/0 ; TRE-LC1 0/0 . Protein lysate from inducible nephron-specific CAP1/Prss8 knockout mice was used for Western blot analysis [17].…”

“…In mice, however, proteolytic ENaC activation and sodium retention in an experimental nephrotic syndrome were independent of a catalytically active CAP1/Prss8 [16]. Kidney-specific CAP1/Prss8 knockout mice maintained ENaC-mediated Na + and K + homeostasis, although through an aldosterone-independent mechanism when Na + -deprived [17]. CAP3/St14 was proposed to form direct physical interactions with CAP1/Prss8 [18], rendering its zymogen form active by proteolytic cleavage [19].…”

Mannan-binding lectin serine protease-2 (MASP-2) in human kidney and its relevance for proteolytic activation of the epithelial sodium channel

“…Several proteases have been shown to activate ENaC in vitro; however, murine gene knockout studies show that the proteases prostasin, kallikrein and TMPRSS4 are dispensable for physiological proteolytic activation 3 , 6 – 10 . Urokinase, which is expressed along the nephron and present in urine, fails also to activate ENaC 5 , 11 .…”