Publications

Gamma-melanocyte stimulating hormone (gamma-MSH) is a circulating natriuretic peptide hormone derived from proopiomelanocortin (POMC); its concentration in plasma and pituitary POMC mRNA abundance, increase in rats ingesting a high-sodium diet (HSD, 8% NaCl) compared with a low-sodium diet (LSD, 0.07% NaCl). RT-PCR of rat kidney RNA demonstrated reaction products of the expected size in both cortex and medulla for MC3-R, MC4-R, and MC5-R mRNA; no signal for MC1-R or MC2-R was detected. Relative to beta-actin or cyclophilin, abundance of the three receptor transcripts after 1 wk of the LSD was approximately equal in both cortex and medulla. After 1 wk of the HSD, mRNA abundance of MC4-R and MC5-R was unchanged, whereas that of MC3-R in medulla more than doubled, the ratio of MC3-R/beta-actin signal increasing from 0.38 +/- 0.04 on LSD to 0.84 +/- 0.04 on HSD (P < 0.001). No significant increase occurred in the cortex. The increase in MC3-R expression induced by dietary sodium was observed in inner medullary collecting duct (IMCD) cells isolated from the kidneys of HSD rats, suggesting that these cells were the major site of receptor expression in the medulla. Immunoblots of whole medullary and IMCD cell homogenates detected MC3-R immunoreactive protein; its expression was twice as great in samples from HSD vs. LSD rat kidneys, paralleling the increase in MC3-R mRNA abundance on the HSD. No changes in MC4-R or MC5-R protein expression were observed. Incubation of IMCD cell suspensions with increasing concentrations of gamma2-MSH led to increased cAMP accumulation, with values from rats on the HSD being roughly double the values from LSD rats. Intrarenal infusion of gamma2-MSH (500 fmol/min) increased sodium and cAMP excretion from the infused but not contralateral kidney of HSD rats, while having no effect in LSD rats. These data show that MC3-R is expressed in rat IMCD cells in a manner modulated by dietary sodium intake. Because MC3-R is the receptor with which gamma-MSH interacts, our findings suggest the existence of a sodium-regulating system, activated in response to a HSD, which increases urinary sodium excretion to balance the high-sodium intake.

Apoptosis is a critical process in normal mammary gland development and the rapid clearance of apoptotic cells prevents tissue injury associated with the release of intracellular antigens from dying cells. Milk fat globule-EGF-factor 8 (Mfge8) is a milk glycoprotein that is abundantly expressed in the mammary gland epithelium and has been shown to facilitate the clearance of apoptotic lymphocytes by splenic macrophages. We report that mice with disruption of Mfge8 had normal mammary gland development until involution. However, abnormal mammary gland remodeling was observed postlactation in Mfge8 mutant mice. During early involution, Mfge8 mutant mice had increased numbers of apoptotic cells within the mammary gland associated with a delay in alveolar collapse and fat cell repopulation. As involution progressed, Mfge8 mutants developed inflammation as assessed by CD45 and CD11b staining of mammary gland tissue sections. With additional pregnancies, Mfge8 mutant mice developed progressive dilatation of the mammary gland ductal network. These data demonstrate that Mfge8 regulates the clearance of apoptotic epithelial cells during mammary gland involution and that the absence of Mfge8 leads to inflammation and abnormal mammary gland remodeling.

OBJECTIVE

Matrix metalloproteinase-2 (MMP-2) plays a major role in dysfunctional ventricular remodeling following myocardial injury induced by ischemia/reperfusion and heart failure. To directly assess the role of MMP-2 in the absence of superimposed injury, we generated cardiac-specific, constitutively active MMP-2 transgenic mice.

METHODS

Morphologic and functional studies were carried out using both intact and demembranated (skinned) right ventricular trabeculae dissected from hearts of 8-month-old MMP-2 transgenic mice and wild-type controls (WT).

RESULTS

Electron micrographs showed that compared to WT, MMP-2 myocardium had no gross, ultrastructural changes (no myocyte dropout or gross fibrosis). However, MMP-2 myocardium contained fibroblasts with abundant rough endoplasmic reticulum, consistent with an activated synthetic phenotype, suggesting extracellular matrix remodeling in MMP-2 trabeculae. Consistent with remodeling, mechanical studies found increased stiffness of intact unstimulated trabeculae (increasing sarcomere lengths from 2 to 2.3 microm caused a greater rise of passive muscle force for MMP-2 trabeculae versus WT). With electrical stimulation, MMP-2 trabeculae generated substantially less active force at all sarcomere lengths. Moreover, inotropic responses to increases of bath [Ca2+], pacing frequency, and isoproterenol were all significantly reduced versus WT trabeculae. Skinned fiber assessment of myofilament function revealed that maximum Ca2+-activated force of skinned MMP-2 trabeculae was reduced to approximately 50% of WT, suggesting a myofilament contraction defect.

CONCLUSION

Cardiac-specific, constitutively active MMP-2 expression leads to impaired contraction and diminished responses to inotropic stimulation. These findings indicate that MMP-2 can directly impair ventricular function in the absence of superimposed injury.

BACKGROUND AND PURPOSE

Mutations in endoglin (ENG) and activin-like kinase (ALK1) cause hereditary hemorrhagic telangiectasias, disorders characterized by pulmonary and brain arteriovenous malformations (BAVMs). We investigated whether polymorphisms in these genes are also associated with sporadic BAVM.

METHODS

A total of 177 sporadic BAVM patients and 129 controls (all subjects white) were genotyped for 2 variants in ALK1 and 7 variants in ENG.

RESULTS

The ALK1 IVS3-35A>G polymorphism was associated with BAVM: (AnyA [AA+AG] genotype: odds ratio, 2.47; 95% CI, 1.38 to 4.44; P=0.002). Two ENG polymorphisms, ENG -1742A>G and ENG 207G>A, showed a trend toward association with BAVM that did not reach statistical significance.

CONCLUSIONS

A common polymorphism in ALK1 is associated with sporadic BAVM, suggesting that genetic variation in genes mutated in familial BAVM syndromes may play a role in sporadic BAVMs.