GCH1 plays a role in the high-altitude adaptation of Tibetans.

Tibetans are well adapted to high-altitude hypoxia. Previous genome-wide scans have reported many candidate genes for this adaptation, but only a few have been studied. Here we report on a hypoxia gene ( GCH1, GTP-cyclohydrolase I), involved in maintaining nitric oxide synthetase (NOS) function and normal blood pressure, that harbors many potentially adaptive variants in Tibetans. We resequenced an 80.8 kb fragment covering the entire gene region of GCH1 in 50 unrelated Tibetans. Combined with previously published data, we demonstrated many GCH1 variants showing deep divergence between highlander Tibetans and lowlander Han Chinese. Neutrality tests confirmed a signal of positive Darwinian selection on GCH1 in Tibetans. Moreover, association analysis indicated that the Tibetan version of GCH1 was significantly associated with multiple physiological traits in Tibetans, including blood nitric oxide concentration, blood oxygen saturation, and hemoglobin concentration. Taken together, we propose that GCH1 plays a role in the genetic adaptation of Tibetans to high altitude hypoxia.

EP300 contributes to high-altitude adaptation in Tibetans by regulating nitric oxide production.

The genetic adaptation of Tibetans to high altitude hypoxia likely involves a group of genes in the hypoxic pathway, as suggested by earlier studies. To test the adaptive role of the previously reported candidate gene EP300 (histone acetyltransferase p300), we conducted resequencing of a 108.9 kb gene region of EP300 in 80 unrelated Tibetans. The allele-frequency and haplotype-based neutrality tests detected signals of positive Darwinian selection on EP300 in Tibetans, with a group of variants showing allelic divergence between Tibetans and lowland reference populations, including Han Chinese, Europeans, and Africans. Functional prediction suggested the involvement of multiple EP300 variants in gene expression regulation. More importantly, genetic association tests in 226 Tibetans indicated significant correlation of the adaptive EP300 variants with blood nitric oxide (NO) concentration. Collectively, we propose that EP300 harbors adaptive variants in Tibetans, which might contribute to high-altitude adaptation through regulating NO production.

Intra-membrane oligomerization and extra-membrane oligomerization of amyloid-ß peptide are competing processes as a result of distinct patterns of motif interplay.

Soluble oligomers of amyloid-ß peptide (Aß) are emerging as the primary neurotoxic species in Alzheimer disease, however, whether the membrane is among their direct targets that mediate the downstream adverse effects remains elusive. Herein, we show that multiple soluble oligomeric Aß preparations, including Aß-derived diffusible ligand, protofibril, and zinc-induced Aß oligomer, exhibit much weaker capability to insert into the membrane than Aß monomer. Aß monomers prefer incorporating into membrane rather than oligomerizing in solution, and such preference can be reversed by the aggregation-boosting factor, zinc ion. Further analyses indicate that the membrane-embedded oligomers of Aß are derived from rapid assembly of inserted monomers but not due to the insertion of soluble Aß oligomers. By comparing the behavior of a panel of Aß truncation variants, we demonstrate that the intra- and extra-membrane oligomerization are mutually exclusive processes that proceed through distinct motif interplay, both of which require the action of amino acids 37-40/42 to overcome the auto-inhibitory interaction between amino acids 29-36 and the N-terminal portion albeit via different mechanisms. These results indicate that intra- and extra-membrane oligomerization of Aß are competing processes and emphasize a critical regulation of membrane on the behavior of Aß monomer and soluble oligomers, which may determine distinct neurotoxic mechanisms.

A redox switch in C-reactive protein modulates activation of endothelial cells.

C-reactive protein (CRP) has been implicated in the regulation of inflammation underlying coronary artery disease; however, little is known about the molecular mechanisms responsible for the expression of its pro- or anti-inflammatory activities. Here, we have identified the intrasubunit disulfide bond as a conserved switch that controls the structure and functions of CRP. Conformational rearrangement in human pentameric CRP to monomeric CRP (mCRP) is the prerequisite for this switch to be activated by reducing agents, including thioredoxin. Immunohistochemical analysis revealed 36-79% colocalization of thioredoxin and mCRP in human advanced coronary atherosclerotic lesions. Nonreduced mCRP was largely inert in activating human coronary artery endothelial cells (HCAECs), whereas reduced or cysteine-mutated mCRP evoked marked release of IL-8 and monocyte chemoattractant protein-1 from HCAECs, with ~50% increase at a concentration of 1 µg/ml. Reduced mCRP was ~4 to 40-fold more potent than mCRP in up-regulating adhesion molecule expression, promoting U937 monocyte adhesion to HCAECs, and inducing cytokine release from rabbit arteries ex vivo and in mice. These actions were primarily due to unlocking the lipid raft interaction motif. Therefore, expression of proinflammatory properties of CRP on endothelial cells requires sequential conformational changes, i.e., loss of pentameric symmetry followed by reduction of the intrasubunit disulfide bond.

Monomeric C-reactive protein activates endothelial cells via interaction with lipid raft microdomains.

Emerging evidence indicates that in addition to native pentameric C-reactive protein (CRP), monomeric CRP (mCRP) also plays an active role in inflammation associated with cardiovascular diseases. mCRP activates endothelial cells, one of the critical events in cardiovascular diseases; however, the underlying molecular mechanisms are incompletely understood. Here we report that association of mCRP with human aortic and coronary artery endothelial cells is predominantly due to membrane insertion rather than binding to the surface proteins Fc gammaRs and proteoglycans. We identify lipid rafts as the preferential membrane microdomains for mCRP anchorage. mCRP binding depends on membrane cholesterol content and is synergistically mediated by the putative cholesterol binding consensus sequence of CRP (aa 35-47) and the C-terminal octapeptide (aa 199-206). Conversely, disrupting lipid rafts with methyl-beta cyclodextrin or nystatin abrogated mCRP-induced cytokine release, reactive oxygen species generation, and adhesion molecule expression in endothelial cells. Furthermore, ex vivo treatment of rabbit thoracic aorta and carotid artery segments with nystatin prevented mCRP-induced IL-8 release. Our data identify mCRP-lipid raft interaction as an important mechanism in mediating cellular responses to mCRP and lend further support to the notion of mCRP regulation of endothelial cell function during inflammation.