Key inflammatory pathways underlying vascular remodeling in pulmonary hypertension.

Independent of the underlying cause, pulmonary hypertension (PH) remains a devastating condition that is characterized by limited survival. Cumulating evidence indicates that in addition to a dysbalance of mediators regulating vascular tone and growth factors promoting vascular remodeling, failure to resolve inflammation and altered immune processes play a pivotal role in the development and progression of PH. Here, we highlight the role of key inflammatory pathways in the pathobiology of vascular remodeling and PH, and discuss potential therapeutic interventions that may halt disease progression or even reverse pulmonary vascular remodeling. Perivascular inflammation is present in all forms of PH, and inflammatory pathways involve numerous mediators and cell types including macrophages, neutrophils, T cells, dendritic cells, and mast cells. Dysfunctional bone morphogenic protein receptor 2 (BMPR2) signaling and dysregulated immunity enable the accumulation of macrophages and other inflammatory cells in obliterative vascular lesions. Regulatory T cells (Tregs) were shown to be of particular relevance in the control of inflammatory responses. Key cytokines/chemokines include interleukin-6, functioning via classic or trans-signaling, macrophage migratory inhibitory factor (MIF), but also other mediators such as neutrophil-derived myeloperoxidase. The expanding knowledge on this topic has resulted in multiple opportunities for sophisticated therapeutic interventions.

Ligand sensitivity of the 2 subunit from the bovine cone cGMP-gated channel is modulated by protein kinase C but not by calmodulin.

1. Homomeric cyclic nucleotide-gated (CNG) channels composed of alpha2 subunits from bovine cone photoreceptors were heterologously expressed in the human embryonic kidney (HEK) 293 cell line. Modulation of cGMP sensitivity by protein kinase C (PKC)-mediated phosphorylation and by binding of calmodulin (CaM) was investigated in inside-out patches. 2. A peptide encompassing the putative CaM-binding site within the N-terminus of the channel protein binds Ca(2+)-CaM with high affinity, yet the ligand sensitivity of alpha2 channels is not modulated by CaM. 3. PKC-mediated phosphorylation increased the activation constant (K(1/2)) for cGMP from 19 to 56 microM and decreased the Hill coefficient (from 2.5 to 1.5). The change in ligand sensitivity involves phosphorylation of the serine residues S577 and S579 in the cGMP-binding domain. The increase in K(1/2) was completely abolished in mutant channels in which the two serine residues were replaced by alanine. 4. An antibody specific for the delta isoform of PKC strongly labels the cone outer segments. 5. Modulation of cGMP affinity of bovine alpha2 CNG channels by phosphorylation could play a role in the regulation of photoreceptor sensitivity.

Interaction of glutamic-acid-rich proteins with the cGMP signalling pathway in rod photoreceptors.

The assembly of signalling molecules into macromolecular complexes (transducisomes) provides specificity, sensitivity and speed in intracellular signalling pathways. Rod photoreceptors in the eye contain an unusual set of glutamic-acid-rich proteins (GARPs) of unknown function. GARPs exist as two soluble forms, GARP1 and GARP2, and as a large cytoplasmic domain (GARP' part) of the beta-subunit of the cyclic GMP-gated channel. Here we identify GARPs as multivalent proteins that interact with the key players of cGMP signalling, phosphodiesterase and guanylate cyclase, and with a retina-specific ATP-binding cassette transporter (ABCR), through four, short, repetitive sequences. In electron micrographs, GARPs are restricted to the rim region and incisures of discs in close proximity to the guanylate cyclase and ABCR, whereas the phosphodiesterase is randomly distributed. GARP2, the most abundant splice form, associates more strongly with light-activated than with inactive phosphodiesterase, and GARP2 potently inhibits phosphodiesterase activity. Thus, the GARPs organize a dynamic protein complex near the disc rim that may control cGMP turnover and possibly other light-dependent processes. Because there are no similar GARPs in cones, we propose that GARPs may prevent unnecessary cGMP turnover during daylight, when rods are held in saturation by the relatively high light levels.