C-type natriuretic peptide (CNP) is an important regulator of skeletal growth. Loss-of-function mutations affecting the CNP receptor natriuretic peptide receptor-B (gene NPR2) cause the autosomal recessive skeletal dysplasia, acromesomelic dysplasia, Maroteaux type (AMDM). The phenotype of heterozygous carriers of NPR2 mutations is less clear. The objective of the study was to determine the phenotypic features of heterozygous carriers of NPR2 mutations. This was a case-control study from the general community. Thirty-nine members of a family in which one member has AMDM were studied. This was an observational study. The primary measure was stature, with the hypothesis that carriers have reduced stature compared with noncarriers. Sixteen family members were NPR2 mutation carriers. Height z-scores of these carriers were -1.8 +/- 1.1 (mean +/- sd), which was significantly less than the 23 noncarrier family members (-0.4 +/- 0.8, P < 0.0005) and the general population (P < 0.0005). However, there was no difference in body proportion between carriers and noncarriers. The proband with AMDM had low IGF-I levels and evidence of GH resistance, as well as very high plasma levels of CNP and its amino-terminal propeptide. Levels of these peptides were normal in the heterozygous carriers. We have shown that heterozygous mutations in NPR2 are associated with short stature. Assuming one in 700 people unknowingly carry an NPR2 mutation, our data suggest that approximately one in 30 individuals with idiopathic short stature are carriers of NPR2 mutations.

Sensitive immunofluorescence and immunoperoxidase techniques were used to test an extensive range of monoclonal antibodies for reactivity with Kupffer cells and interstitial dendritic cells (DCs) in cryostat-cut sections of human liver. Leucocytes with a dendritic cell morphology were identified with CD45 (antileucocyte common) reagents in portal tracts, predominantly around bile ducts, and these cells stained strongly for the HLA-DP, DQ, and DR antigens. Kupffer cells stained less intensely with anti-class-II reagents, particularly anti-HLA-DQ. The interstitial DCs expressed the LFA-1 antigen but failed to stain with CD11b, CD11c, and the defined T and B cell CD antibodies; nor did they stain with antibodies to FcR1, FcR11, FcRIII, or the C3b receptor. Of the myeloid monoclonal antibodies available from the 3rd Leucocyte Differentiation Antigen Workshop, only Y2/131, Ki-M7, Ki-M8, and a minority of CD14 antibodies stained DCs, whereas Kupffer cells showed a wider reactivity with antimacrophage antibodies including those of workshop groups 11, 15, 16, and other unique antibodies. A 2nd probable DC population was identified in the liver capsule that had a similar phenotype to portal interstitial DCs. Although some minor phenotypic differences between liver portal DCs and the phenotypes of Langerhans cells and isolated tonsil DCs were noted, our results support the view that there is a unique hemopoietic lineage of DCs. The presence of DCs, which stimulate strong allogeneic T cell responses, in the portal triads is consistent with the fact that the histologic changes of graft-versus-host disease seen in bone marrow transplantation and the lymphocytic infiltrate in a rejecting liver allograft occur predominantly in the periportal region.

Background: C-type natriuretic peptide (CNP)/natriuretic peptide receptor 2 (NPR2) signaling is essential for long bone growth. Enhanced CNP production caused by chromosomal translocations results in tall stature, a Marfanoid phenotype, and skeletal abnormalities. A similar phenotype was described in a family with an activating NPR2 mutation within the guanylyl cyclase domain. Case: Here we describe an extremely tall male without skeletal deformities, with a novel NPR2 mutation (p.Arg655Cys) located in the kinase homology domain. Objectives: The objective of the study was to investigate the functional and structural effects of the NPR2 mutation. Methods: Guanylyl cyclase activities of wild-type vs mutant NPR2 were analyzed in transfected human embryonic kidney 293 cells and in skin fibroblasts. The former were also used to study possible interactions between both isoforms. Homology modeling was performed to understand the molecular impact of the mutation. Results: CNP-stimulated cGMP production by the mutant NPR2 was markedly increased in patient skin fibroblasts and transfected human embryonic kidney 293 cells. The stimulatory effects of ATP on CNP-dependent guanylyl cyclase activity were augmented, suggesting that this novel mutation enhances both the responsiveness of NPR2 to CNP and its allosteric modulation/stabilization by ATP. Coimmunoprecipitation showed that wild-type and mutant NPR2 can form stable heterodimers, suggesting a dominant-positive effect. In accordance with augmented endogenous receptor activity, plasma N-terminal pro-CNP (a marker of CNP production in tissues) was reduced in the proband. Conclusions: We report the first activating mutation within the kinase homology domain of NPR2, resulting in extremely tall stature. Our observations emphasize the important role of this domain in the regulation of guanylyl cyclase activity and bone growth in response to CNP.

Production and clearance of plasma C-type natriuretic peptide (CNP) and amino terminal (NT)-proCNP immunoreactivity in the human circulation remain poorly characterized. Accordingly, we have measured arterial and venous concentrations of CNP and NT-proCNP across multiple tissue beds during cardiac catheterization in 120 subjects (age: 64.2±9.0 years; 73% men) investigated for cardiovascular disorders. The heart, head and neck, and musculoskeletal tissues made the clearest contributions to both plasma CNP and NT-proCNP ( P <0.05). Net release of NT-proCNP was also observed from hepatic tissue ( P <0.001). Negative arteriovenous gradients for CNP were observed across renal, hepatic, and pulmonary tissue ( P <0.05), indicating net clearance, whereas no tissue-specific site of NT-proCNP clearance was identified. Age, mean pulmonary artery pressure, left ventricular end diastolic pressure, Brandt score of myocardial jeopardy, and troponin I were independent predictors of circulating CNP levels in multivariable analysis. Sex and kidney function were independently predictive of arterial NT-proCNP. The proportional step-up of CNP (+60%) across the heart was less than for brain natriuretic peptide (+123%) but greater than for NT–pro-brain natriuretic peptide (NT-proBNP) (+36%) and NT-proCNP (+42%; P <0.001 for all). We conclude that cardiac and head and neck tissue are important sources of CNP. Circulating CNP but not NT-proCNP concentrations are related to cardiac hemodynamic load and ischemic burden. Although cardiac release is most evident, multiple additional tissues release NT-proCNP immunoreactivity without evidence for an organ-specific site for NT-proCNP degradation. Taken together, differences in magnitude and direction of transorgan gradients for CNP compared with NT-proCNP suggest net generalized cosecretion with differing mechanisms of clearance.