BMPR2 mutation alters the lung macrophage endothelin-1 cascade in a mouse model and patients with heritable pulmonary artery hypertension.

Macrophage derived-endothelin-1 (ET-1) has been suggested to contribute to a number of chronic lung diseases. Whether the ET-1 cascade from non-vascular sources (inflammatory cells) also contributes to pulmonary artery hypertension (PAH) and in particular to heritable PAH (HPAH) with known bone morphogenetic protein type 2 receptor (BMPR2) mutations is not known. We tested this notion using bone marrow-derived macrophages (BMDM; precursors of tissue macrophages) isolated from ROSA26rtTAXTetO(7)-tet-BMPR2(R899X) mice (model of PAH with universal expression of a mutated BMPR2 gene) with and without activation by LPS and in human lung tissue from HPAH with BMPR2 mutations and idiopathic PAH (IPAH). At baseline ET(A) and ET(B) receptors and endothelin converting enzyme (ECE) gene expression was reduced in BMPR2 mutant BMDM compared with controls. In control BMDM, LPS resulted in increased ppET-1 gene expression and ET-1 in culture media, whereas ET(A) and ET(B) receptor and ECE gene expression was decreased. These findings were more severe in BMPR2 mutant BMDM. Antagonism of the ET(B) receptor resulted in increased ET-1 in the media, suggesting that decreased ET-1 uptake by the ET(B) receptor contributes to the elevation. While ET-1 expression was demonstrated in lung macrophages from controls and IPAH and HPAH patients, ET(A) and ET(B) expression was decreased in the HPAH, but not IPAH, patients compared with controls. We conclude that reduced expression of macrophage ET-1 receptors in HPAH increases lung ET-1 and may contribute to the pathogenesis and maintenance of HPAH. This is the first description of protein expression that distinguishes HPAH from IPAH in patients.

Human trabecular meshwork cells secrete neurotrophins and express neurotrophin receptors (Trk).

PURPOSE: The purpose of this study was to compare the mRNA expression of neurotrophins (NTs) and NT receptors (Trk) in cultured human trabecular meshwork (HTM) cells and ex vivo HTM tissues, to immunolocalize both NT and Trk receptors in cultured HTM cells, and to demonstrate secretion of NTs by HTM cells. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expression of NT and Trk receptor mRNAs in early-passaged, cultured HTM cells from donors of several ages. RT-PCR was used on ex vivo HTM tissues from donors to compare and contrast mRNA expression with cell culture results. In addition, immunohistochemistry was used to localize the translated NT and low- (p75) and high- (Trk) affinity NT receptor proteins within cultured HTM cells and trabecular meshwork tissues. Last, enzyme-linked immunoassay (ELISA) was used to demonstrate secretion of NTs by HTM cells. RESULTS: Amplification products of the expected size for NTs were detected in both cultured HTM cells and ex vivo HTM tissues. Specifically identified were amplification products for the following NTs: NGF, BDNF, NT-3, and NT-4. Amplification products for the full-length Trk A and Trk C high-affinity receptor were observed, as well as truncated isoforms for Trk B and Trk C. No amplification products were produced for the full-length Trk B receptor nor for the low-affinity p75 receptor. Immunohistochemistry indicated that proteins for the various NTs and full-length and truncated Trk receptors were translated by cultured HTM cells and tissues. Immunoassays (ELISA) detected BDNF, NT-4, NGF, and NT-3 in the culture media from HTM cells. CONCLUSIONS: The results demonstrate, for the first time, mRNA expression for NT and Trk receptors by both cultured HTM cells and ex vivo HTM tissues. NTs were immunolocalized in HTM tissues and cultured HTM cells are capable of secreting NTs. Specific NTs acting through high-affinity Trk receptors within the HTM may be involved in maintaining the normal function of this complex tissue.

Fas-activated apoptosis and apoptosis mediators in human trabecular meshwork cells.

A gradual loss of cells occurs within the human trabecular meshwork during normal aging and appears to be increased in patients with primary open-angle glaucoma. The exact mechanism by which cells are lost in either condition is not known, however phagocytosis, cell migration and cell death have been suggested. Apoptosis is one method by which cell death can occur. We have examined the modulators for apoptosis within the human trabecular meshwork using both cell lines and ex-vivo dissected trabecular meshwork tissues obtained from normal donors. Using RT-PCR it was shown that mRNA for several modulators of apoptosis (Fas, Bcl-2, Bcl-xl, Bax, and ICE) are expressed by both cell lines and ex-vivo tissues. Apoptosis was stimulated to occur by treating cell lines with a monoclonal antibody (IgM) to Fas. Apoptosis was verified via morphological changes to the cells, transferase-mediated dUTP nick-end labeling TUNEL Immunofluorescence, and DNA laddering. Control cells exposed to IgM did not undergo apoptosis. These results represent the first report of apoptosis modulators within the human trabecular meshwork and demonstrate that human trabecular meshwork cells can be stimulated to undergo apoptosis via the Fas/FasL pathway.