The C-terminal cleavage of angiotensin II and III is mediated by prolyl carboxypeptidase in human umbilical vein and aortic endothelial cells

The renin-angiotensin system, with the octapeptide angiotensin II as key player, is important in the renal, cardiac and vascular physiology. Prolyl carboxypeptidase (PRCP), prolyl endopeptidase (PREP) and angiotensin converting enzyme 2 (ACE2) are reported to be involved in the conversion of angiotensin II to angiotensin (1-7). Previous investigations showed that the processing of angiotensin II is cell- and species-specific and little is known about its conversion in human endothelial cells. Therefore, we aimed to investigate the C-terminal processing of angiotensin II and III in comparison to the processing of des-Arg⁹-bradykinin in human endothelial cells. To this end, human umbilical vein and aortic endothelial cells (HUVEC and HAoEC) were incubated with the peptides for different time periods. Mass spectrometry analysis was performed on the supernatants to check for cleavage products. Contribution of PRCP, ACE2 and PREP to the peptide cleavage was evaluated by use of the selective inhibitors compound 8o, DX600 and KYP-2047. The use of these selective inhibitors revealed that the C-terminal cleavage of angiotensin II and III was PRCP-dependent in HUVEC and HAoEC. In contrast, the C-terminal cleavage of des-Arg⁹-bradykinin was PRCP-dependent in HUVEC and PRCP- and ACE2-dependent in HAoEC. With this study, we contribute to a better understanding of the processing of peptides involved in the alternative renin-angiotensin system. We conclude that PRCP is the main enzyme for the C-terminal processing of angiotensin peptides in human umbilical vein and aortic endothelial cells. For the first time the contribution of PRCP was investigated by use of a selective PRCP-inhibitor.

Prolyl carboxypeptidase in Agouti-related Peptide neurons modulates food intake and body weight

Objective

Prolyl carboxypeptidase (PRCP) plays a role in the regulation of energy metabolism by inactivating hypothalamic α-melanocyte stimulating hormone (α-MSH) levels. Although detected in the arcuate nucleus, limited PRCP expression has been observed in the arcuate POMC neurons, and its site of action in regulating metabolism is still ill-defined.

Methods

We performed immunostaining to assess the localization of PRCP in arcuate Neuropeptide Y/Agouti-related Peptide (NPY/AgRP) neurons. Hypothalamic explants were then used to assess the intracellular localization of PRCP and its release at the synaptic levels. Finally, we generated a mouse model to assess the role of PRCP in NPY/AgRP neurons of the arcuate nucleus in the regulation of metabolism.

Results

Here we show that PRCP is expressed in NPY/AgRP-expressing neurons of the arcuate nucleus. In hypothalamic explants, stimulation by ghrelin increased PRCP concentration in the medium and decreased PRCP content in synaptic extract, suggesting that PRCP is released at the synaptic level. In support of this, hypothalamic explants from mice with selective deletion of PRCP in AgRP neurons (Prcp^AgRPKO) showed reduced ghrelin-induced PRCP concentration in the medium compared to controls mice. Furthermore, male Prcp^AgRPKO mice had decreased body weight and fat mass compared to controls. However, this phenotype was sex-specific as female Prcp^AgRPKO mice show metabolic differences only when challenged by high fat diet feeding. The improved metabolism of Prcp^AgRPKO mice was associated with reduced food intake and increased energy expenditure, locomotor activity, and hypothalamic α-MSH levels. Administration of SHU9119, a potent melanocortin receptor antagonist, selectively in the PVN of Prcp^AgRPKO male mice increased food intake to a level similar to that of control mice.

Conclusions

Altogether, our data indicate that PRCP is released at the synaptic levels and that PRCP in AgRP neurons contributes to the modulation of α-MSH degradation and related metabolic control in mice.

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PRCP is expressed in the arcuate NPY/AgRP neurons.

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PRCP is released in the synaptic space following ghrelin stimulation.

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Male mice with PRCP deletion in NPY/AgRP neurons show leaner phenotype with decreased food intake on standard chow diet.

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Female mice with PRCP deletion in NPY/AgRP neurons show leaner phenotype with decreased food intake only on high fat diet.

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Selective blockade of PVN melanocortin receptors increases feeding in male mice with PRCP deletion in NPY/AgRP neurons.

Prolyl carboxypeptidase mRNA expression in the mouse brain

Prolyl carboxypeptidase (PRCP), a serine protease, is widely expressed in the body including liver, lung, kidney and brain, with a variety of known substrates such as plasma prekallikrein, bradykinin, angiotensins II and III, and α-MSH, suggesting its role in the processing of tissue-specific substrates. In the brain, PRCP has been shown to inactivate hypothalamic α-MSH, thus modulating melanocortin signaling in the control of energy metabolism. While its expression pattern has been reported in the hypothalamus, little is known on the distribution of PRCP throughout the mouse brain. This study was undertaken to determine PRCP expression in the mouse brain. Radioactive in situ hybridization was performed to determine endogenous PRCP mRNA expression. In addition, using a gene-trap mouse model for PRCP deletion, X-gal staining was performed to further determine PRCP distribution. Results from both approaches showed that PRCP gene is broadly expressed in the brain.

Ghrelin regulates hypothalamic prolyl carboxypeptidase expression in mice

Hypothalamic Prolyl carboxypeptidase (PRCP) plays a role in the regulation of energy metabolism by inactivating hypothalamic α-melanocyte stimulating hormone (α-MSH) levels and thus affecting melanocortin signaling. Alpha-MSH production is highly regulated both at transcriptional and posttranslational levels. Here we show that fasting induces a hypothalamic-specific up-regulation of Prcp mRNA and protein levels. Since fasting is characterized by elevated circulating ghrelin levels, we tested the effect of peripheral and central administration of ghrelin, and found that ghrelin increases hypothalamic Prcp mRNA expression. No changes in Prcp mRNA levels were detected in ghrelin knockout mice compared to their controls. Finally, ghrelin effect on PRCP expression was ghrelin receptor-mediated. Altogether our data show that ghrelin is a key regulator of hypothalamic PRCP expression, and up-regulation of PRCP by ghrelin may be an additional mechanism to decrease melanocortin signaling.