Carboxypeptidases E and D

Cpxm2 as a novel candidate for cardiac hypertrophy and failure in hypertension

Treatment of hypertension-mediated cardiac damage with left ventricular (LV) hypertrophy (LVH) and heart failure remains challenging. To identify novel targets, we performed comparative transcriptome analysis between genetic models derived from stroke-prone spontaneously hypertensive rats (SHRSP). Here, we identified carboxypeptidase X 2 (Cpxm2) as a genetic locus affecting LV mass. Analysis of isolated rat cardiomyocytes and cardiofibroblasts indicated Cpxm2 expression and intrinsic upregulation in genetic hypertension. Immunostaining indicated that CPXM2 associates with the t-tubule network of cardiomyocytes. The functional role of Cpxm2 was further investigated in Cpxm2-deficient (KO) and wild-type (WT) mice exposed to deoxycorticosterone acetate (DOCA). WT and KO animals developed severe and similar systolic hypertension in response to DOCA. WT mice developed severe LV damage, including increases in LV masses and diameters, impairment of LV systolic and diastolic function and reduced ejection fraction. These changes were significantly ameliorated or even normalized (i.e., ejection fraction) in KO-DOCA animals. LV transcriptome analysis showed a molecular cardiac hypertrophy/remodeling signature in WT but not KO mice with significant upregulation of 1234 transcripts, including Cpxm2, in response to DOCA. Analysis of endomyocardial biopsies from patients with cardiac hypertrophy indicated significant upregulation of CPXM2 expression. These data support further translational investigation of CPXM2.

Emergence of anxiety-like behaviours in depressive-like Cpe(fat/fat) mice

Cpe(fat/fat) mice have a point mutation in carboxypeptidase E (Cpe), an exopeptidase that removes C-terminal basic amino acids from intermediates to produce bioactive peptides. The mutation renders the enzyme inactive and unstable. The absence of Cpe activity in these mutants leads to abnormal processing of many peptides, with elevated levels of intermediates and greatly reduced levels of the mature peptides. Cpe(fat/fat) mice develop obesity, diabetes and infertility in adulthood. We examined whether anxiety- and/or depressive-like behaviours are also present. Anxiety-like responses are not evident in young Cpe(fat/fat) mice (∼60 d), but appear in older animals (>90 d). These behaviours are reversed by acute treatment with diazepam or fluoxetine. In contrast, increased immobilities in forced swim and tail suspension are evident in all age groups examined. These behaviours are reversed by acute administration of reboxetine. In comparison acute treatments with fluoxetine or bupropion are ineffective; however, immobility times are normalized with 2 wk treatment. These data demonstrate that Cpe(fat/fat) mice display depressive-like responses aged ∼60 d, whereas anxiety-like behaviours emerge ∼1 month later. In tail suspension, the reboxetine findings show that noradrenergic actions of antidepressants are intact in Cpe(fat/fat) mice. The ability of acute fluoxetine treatment to rescue anxiety-like while leaving depressive-like responses unaffected suggests that serotonin mechanisms underlying these behaviours are different. Since depressive-like responses in the Cpe(fat/fat) mice are rescued by 2 wk, but not acute, treatment with fluoxetine or bupropion, these mice may serve as a useful model that resembles human depression.

Effect of Voluntary Exercise on Genetically ObeseCpefat/fatMice: Quantitative Proteomics of Serum

OBJECTIVE

To compare the effect of voluntary exercise on body weight, food consumption, and levels of serum proteins between wild-type and carboxypeptidase E-deficient (Cpefat/fat) mice.

RESEARCH METHODS AND PROCEDURES

Study 1 consisted of three groups of female mice: Cpefat/fat mice with continuous access to exercise wheels for 3 weeks (n = 4); wild-type C57BKS mice with access to exercise wheels for 3 weeks (n = 4); and sedentary Cpefat/fat mice (n = 3). Activity, body weight, and food consumption were monitored for this period and a subsequent 9-week period without exercise wheels. Study 2 consisted of four groups of male mice (n = 6 to 7 each): Cpefat/fat mice with exercise wheels, wild-type mice with exercise wheels, and Cpefat/fat and wild-type mice without exercise wheels. Body weight and food consumption were measured over 4 weeks. Sera were collected, and the protein profile was determined by 2-dimensional gel electrophoresis and mass spectrometry.

RESULTS

Cpefat/fat mice were moderately hyperphagic but lost weight during the initial exercise period because of greater energy expenditure. The effect of exercise was temporary, and the mice gained weight after the second week. Several serum proteins were found to be altered by exercise: haptoglobin was decreased by exercise in Cpefat/fat mice, and several kallikreins were increased by exercise in wild-type mice.

DISCUSSION

The access to exercise wheels provided an initial weight loss in Cpefat/fat mice, but this effect was offset by elevated food consumption. The serum proteomics results indicated that Cpefat/fat and wild-type mice differed in their response to exercise.

Characterization of Drosophila carboxypeptidase D

Metallocarboxypeptidase D (CPD), is a 180-kDa protein that contains three carboxypeptidase-like domains, a transmembrane domain, and a cytosolic tail and which functions in the processing of proteins that transit the secretory pathway. An initial report on the Drosophila melanogaster silver gene indicated a CPD-like protein with only two and a half carboxypeptidase-like domains with no transmembrane region (Settle, S. H., Jr., Green, M. M., and Burtis, K. C. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 9470-9474). A variety of bioinformatics and experimental approaches were used to determine that the Drosophila silver gene corresponds to a CPD-like protein with three carboxypeptidase-like domains, a transmembrane domain, and a cytosolic tail. In addition, two alternative exons were found, which result in proteins with different carboxypeptidase-like domains, termed domains 1A and 1B. Northern blot, reverse transcriptase PCR, and sequence analysis were used to confirm the presence of the various mRNA forms. Individual domains of Drosophila CPD were expressed in insect Sf9 cells using the baculovirus expression system. Media from domain 1B- and domain 2-expressing cells showed substantial enzymatic activity, whereas medium from domain 1A-expressing cells was no different from cells infected with wild-type virus. Domains 1B and 2 were purified, and the enzymatic properties were examined. Both enzymes cleaved substrates with C-terminal Arg or Lys, but not Leu, and were inhibited by conventional metallopeptidase inhibitors and some divalent cations. Drosophila domain 1B is more active at neutral pH and greatly prefers C-terminal Arg over Lys, whereas domain 2 is more active at pH 5-6 and slightly prefers C-terminal Lys over Arg. The differences in pH optima and substrate specificity between Drosophila domains 1B and 2 are similar to the differences between duck CPD domains 1 and 2, suggesting that these properties are essential to CPD function.