Fibronectin in formation and degradation of the pericellular matrix

Monoclonal Antibody to Marinobufagenin Downregulates TGFβ Profibrotic Signaling in Left Ventricle and Kidney and Reduces Tissue Remodeling in Salt-Sensitive Hypertension

Background Elevated levels of an endogenous Na/K-ATPase inhibitor marinobufagenin accompany salt-sensitive hypertension and are implicated in cardiac fibrosis. Immunoneutralization of marinobufagenin reduces blood pressure in Dahl salt-sensitive (Dahl-S) rats. The effect of the anti-marinobufagenin monoclonal antibody on blood pressure, left ventricular (LV) and renal remodeling, and gene expression were investigated in hypertensive Dahl-S rats. Methods and Results Dahl-S rats were fed high NaCl (8%, HS; n=14) or low NaCl (0.1%, LS; n=14) diets for 8 weeks. Animals were administered control antibody (LS control antibody, LSC; HS control antibody, HSC; n=7 per group) or anti-marinobufagenin antibody once on week 7 of diet intervention (n=7 per group). Levels of marinobufagenin, LV, and kidney mRNAs and proteins implicated in profibrotic signaling were assessed. Systolic blood pressure was elevated (211±8 versus 133±3 mm Hg, P<0.01), marinobufagenin increased 2-fold in plasma (P<0.05) and 5-fold in urine (P<0.01), LV and kidney weights increased, and levels of LV collagen-1 rose 3.5-fold in HSC versus LSC. Anti-marinobufagenin antibody treatment decreased systolic blood pressure by 24 mm Hg (P<0.01) and reduced organ weights and level of LV collagen-1 (P<0.01) in hypertensive Dahl salt-sensitive rats with anti-marinobufagenin antibody versus HSC. The expression of genes related to transforming growth factor-β-dependent signaling was upregulated in the left ventricles and kidneys in HSC versus LSC groups and became downregulated following administration of anti-marinobufagenin antibody to hypertensive Dahl-S rats. Marinobufagenin also activated transforming growth factor-β signaling in cultured ventricular myocytes from Dahl-S rats. Conclusions Immunoneutralization of heightened marinobufagenin levels in hypertensive Dahl-S rats resulted in a downregulation of genes implicated in transforming growth factor-β pathway, which indicates that marinobufagenin is an activator of profibrotic transforming growth factor-β-dependent signaling in salt-sensitive hypertension.

Kinetics of transforming growth factor-beta1 and extracellular matrix in renal tubulointerstitial lesions of mercuric chloride-treated Brown Norway rats

Renal tubulointerstitial lesions in mercuric chloride(HgCl2)-treated Brown Norway rats were investigated focusing on the kinetics of transforming growth factor-beta1(TGF-beta1) and extracellular matrix (ECM). Rats were injected with 1 mg/kg b.w. of HgCl2 at days 0, 2, and 4, and 5 rats were killed at days 2, 4, 6, 8, 10, and 20, respectively. TGF-beta1 mRNA expression in the renal cortex measured by competitive RT-PCR method reached a peak at day 6, mildly decreased at days 8 and 10, and increased again toward day 20. Signals of TGF-beta1 mRNA examined by in situ hybridization method were recognized in the regenerative tubular epithelium at day 6, and in both tubular epithelium and infiltrated mononuclear cells at day 20. After tubular injury, strong immunoreactivity to TGF-beta1 protein was found in desquamated tubular epithelial cells. Then, positive staining was found in the regenerative tubular epithelial cells. Later, infiltrated mononuclear cells also became positive for TGF-beta1 protein. In the ECM, deposition of fibronectin was prominent throughout the experimental period. In conclusion, this strongly suggests that TGF-beta1 derived from tubular epithelial cells and some macrophages might be related to the development of renal interstitial fibrosis in HgCl2-treated BN rats.

Activated human peripheral blood neutrophils produce epithelial injury and fibronectin breakdown in vitro

The ability of peripheral blood neutrophils to injure elements of the alveolar septum was assessed. Experiments consisted of activating previously isolated neutrophils (PMNs) with a soluble (phorbol myristate acetate, PMA) and a particulate (zymosan) trigger, and measuring detachment of 51Cr-labeled epithelial cells. In addition, the mechanisms of epithelial injury were investigated by including anti-proteinase and antioxidants in the system. Untriggered PMNs produced only slight detachment injury to epithelial cells at two effector-target cell ratios, this effect being dramatically increased after triggering with PMA; zymosan caused triggering but less than was produced by PMA. Alpha-1-protease inhibitor produced a decrease in detachment when both PMA- and zymosan-triggered cells were the effectors; superoxide dismutase did not significantly reduce detachment. The ability of triggered PMNs to cause proteolysis of fibronectin, as measured in a radiolabeled fibronectin matrix degradation assay, was related to their triggerability in the detachment assay, zymosan being largely ineffective in triggering enhanced proteolysis. These findings suggest that fibronectin is important in maintaining the integrity of the alveolar epithelial surfaces. Furthermore, in inflamed alveoli, activated PMNs can release proteinases, which cause degradation of this matrix component leading to compromise of the alveolar epithelial barrier.

Determination of fibronectin and its degradation products in bronchoalveolar lavage fluid

In order to estimate, in sarcoidosis, the extent of degradation and the availability of functionally active fibronectin (FN) in the alveolar space, native and total (= native + degraded) FN were determined in the bronchoalveolar lavage (BAL) fluid of 28 non-smoking patients with sarcoidosis, 12 healthy non-smokers and 24 asymptomatic smokers. The FN was measured in unconcentrated BAL fluid in the presence of the protease inhibitor aprotinin: total FN was assayed by a double-antibody sandwich enzyme-linked immunoadsorbent assay (ELISA) and native FN by a gelatin-antibody sandwich ELISA. Both in controls and in sarcoid patients, concentrations of native FN were lower than those of total FN, indicating that FN is degraded in the alveolar space. Compared to non-smoking controls, the sarcoid patients had significantly increased concentrations of both native and total FN (p less than 0.001 for both) in the BAL fluid. Native FN in percentage of total FN was similar in non-smoking sarcoids and controls, representing about 80% and 70%, respectively. In contrast, native FN corresponded to only 30% in the group of control smokers, indicating higher degradation in smokers. Thus, in smokers, less intact collagen-binding FN is available for forming an extracellular matrix, which may be necessary for repair. On the other hand, the elevation of FN, especially in its native form, in sarcoidosis implies that more of it may be available for repair but, if in excess, also for the build-up of fibrotic tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of an alternatively spliced site in human plasma fibronectin that mediates cell type-specific adhesion

We have compared the molecular specificities of the adhesive interactions of melanoma and fibroblastic cells with fibronectin. Several striking differences were found in the sensitivity of the two cell types to inhibition by a series of synthetic peptides modeled on the Arg-Gly-Asp-Ser (RGDS) tetrapeptide adhesion signal. Further evidence for differences between the melanoma and fibroblastic cell adhesion systems was obtained by examining adhesion to proteolytic fragments of fibronectin. Fibroblastic BHK cells spread readily on fl3, a 75-kD fragment representing the RGDS-containing, "cell-binding" domain of fibronectin, but B16-F10 melanoma cells could not. The melanoma cells were able to spread instead on f9, a 113-kD fragment derived from the large subunit of fibronectin that contains at least part of the type III connecting segment difference region (or "V" region); f7, a fragment from the small fibronectin subunit that lacks this alternatively spliced polypeptide was inactive. Monoclonal antibody and fl3 inhibition experiments confirmed the inability of the melanoma cells to use the RGDS sequence; neither molecule affected melanoma cell spreading, but both completely abrogated fibroblast adhesion. By systematic analysis of a series of six overlapping synthetic peptides spanning the entire type III connecting segment, a novel attachment site was identified in a peptide near the COOH-terminus of this region. The tetrapeptide sequence Arg-Glu-Asp-Val (REDV), which is somewhat related to RGDS, was present in this peptide in a highly hydrophilic region of the type III connecting segment. REDV appeared to be functionally important, since this synthetic tetrapeptide was inhibitory for melanoma cell adhesion to fibronectin but was inactive for fibroblastic cell adhesion. REDV therefore represents a novel adhesive recognition signal in fibronectin that possesses cell type specificity. These results suggest that, for some cell types, regulation of the adhesion-promoting activity of fibronectin may occur by alternative mRNA splicing.