The renin-angiotensin system (RAS) is a key biochemical pathway controlling homeostasis and
blood pressure. The initial step of the RAS is carried out by renin to produce angiotensin (Ang)
I which is converted to Angll by the angiotensin-converting enzyme (ACE). Renin is
synthesized as a pro-enzyme which can be activated in dense core granules of the renal
juxtaglomerular cells or released as prorenin. There is evidence that prorenin can, in addition, be
activated in a reversible manner, via a prorenin receptor. Recently, a specific (pro)renin receptor
was identified in human tissues. Binding ofthis receptor to (pro)renin caused increased cleavage
of angiotensinogen and stimulation of an intracellular signalling pathway. The aim of this thesis
is to investigate the biology of prorenin, its maturation and the (pro)renin receptor.
Expression of the mouse putative (pro)renin receptor (RR) was detected by RT-PCR in all
tissues and cell lines examined including human mesangial cells previously reported to be
negative for RR. Mouse RR was also present during development from E9.5. The mouse and rat
RR cDNA were found to be highly homologous (92% and 91%, respectively) to the human
cDNA. Surprisingly, the translated human, mouse and rat cDNAs exhibited sequence identity
with a small protein co-purifying with a bovine vacuolar-ATPase called M8-9 which had not
been reported previously. V-ATPases are critical for cell survival. Phylogenic studies revealed
RR is highly conserved between species and likely to be important physiologically. The role of
RR was investigated in a high circulating prorenin rat model [TGR(Cyplal-Ren2)], in which
(pro)renin triggers malignant hypertension (MH).
Uptake of prorenin by the heart previously demonstrated in this transgenic model may be
mediated by RR. In the present study, the animals, from a new colony, had a gradual
hypertensive response. Cardiovascular stiffening was measured using echo(cardio)graphy.
Despite an obvious hypertrophic remodeling and longer exposure to the inducer, no signs of
microinfarctions or inflammatory infiltration cells were observed in the heart. Fibrinoid necrosis
of small intra-renal vessels with glomerulosclerosis and mesenteric artery remodeling were also
observed. The phenotype differs from the original work. Surprisingly, RR was not up-regulated.
The reasons for the phenotypic differences between TGR(Cyplal-Ren2) colonies were
examined. Two main observations were made: dietary sodium levels appear to correlate with the
severity of MH and TGR(Cyplal-Ren2) animals reported in this thesis had a lower pathogen
To investigate the possible role of RR, a prorenin decoy peptide was used to attempt to
ameliorate the MH phenotype in TGR(Cyplal-Ren2) animals. This peptide which competes
with prorenin for binding to RR, has been showed to improve vascular injuries in diabetic
nephropathy. In TGR(Cyplal-Ren2), however, no changes in the MH phenotype could be
observed, except in the mesentery in which less severe fibrinoid necrosis developed.
To complement work on RR, prorenin maturation and renin storage were studied during
development. The data showed the complete absence of renin granules in mouse kidneys before
birth. This indicates that renin could not be stored and may not be processed through the
regulated pathway as observed in the adult. Low sodium diet and ACE inhibition triggered
(pro)renin granules to be produced in the foetal kidney. Two ACE inhibitors differing in their
ability to cross the placenta were used. The data suggest that foetal renin granule formation is
under dual control from both foetal and maternal RAS.
Although the (pro)renin receptor may be important physiologically, the data presented in this
thesis suggest a more fundamental role in cell biology than had previously been recognised. The
lack of evidence for regulation of RR in a model of high prorenin and malignant hypertension
suggests that the function of this protein may need to be re-assessed.