Description: β-glucans, which can activate innate immune responses, are a major component in the cell wall of the cyst form of Pneumocystis . In the current study, we examined whether β-1,3-glucans are masked by surface proteins in Pneumocystis and what role β-glucans play in Pneumocystis -associated inflammation. For 3 species, including Pneumocystis jirovecii , which causes Pneumocystis pneumonia in humans, Pneumocystis carinii , and Pneumocystis murina , β-1,3-glucans were masked in most organisms, as demonstrated by increased exposure following trypsin treatment. Using quantitative polymerase chain reaction and microarray techniques, we demonstrated in a mouse model of Pneumocystis pneumonia that treatment with caspofungin, an inhibitor of β-1,3-glucan synthesis, for 21 days decreased expression of a broad panel of inflammatory markers, including interferon , tumor necrosis factor α, interleukin 1β, interleukin 6, and multiple chemokines/chemokine ligands. Thus, β-glucans in Pneumocystis cysts are largely masked, which likely decreases innate immune activation; this mechanism presumably was developed for interactions with immunocompetent hosts, in whom organism loads are substantially lower. In immunosuppressed hosts with a high organism burden, organism death and release of glucans appears to be an important contributor to deleterious host inflammatory responses.

Description: Dendritic cells (DCs) comprise distinct populations with specialized immune-regulatory functions. However, the environmental factors that determine the differentiation of these subsets remain poorly defined. Here, we report that retinoic acid (RA), a vitamin A derivative, controls the homeostasis of pre-DC (precursor of DC)–derived splenic CD11b + CD8α – Esam high DCs and the developmentally related CD11b + CD103 + subset within the gut. Whereas mice deprived of RA signaling significantly lost both of these populations, neither pre-DC–derived CD11b – CD8α + and CD11b – CD103 + nor monocyte-derived CD11b + CD8α – Esam low or CD11b + CD103 – DC populations were deficient. In fate-tracking experiments, transfer of pre-DCs into RA-supplemented hosts resulted in near complete conversion of these cells into the CD11b + CD8α – subset, whereas transfer into vitamin A–deficient (VAD) hosts caused diversion to the CD11b – CD8α + lineage. As vitamin A is an essential nutrient, we evaluated retinoid levels in mice and humans after radiation-induced mucosal injury and found this conditioning led to an acute VAD state. Consequently, radiation led to a selective loss of both RA-dependent DC subsets and impaired class II–restricted auto and antitumor immunity that could be rescued by supplemental RA. These findings establish a critical role for RA in regulating the homeostasis of pre-DC–derived DC subsets and have implications for the management of patients with immune deficiencies resulting from malnutrition and irradiation.

Description: Peroxisome proliferator-activated receptor γ (PPARγ) ligands have been widely used to treat type 2 diabetes mellitus. However, knowledge of PPARγ signaling remains incomplete. In addition to PPARγ, these drugs also activate G protein-coupled receptor 40 (GPR40), a Gαq-coupled free fatty acid receptor linked to MAPK networks and glucose homeostasis. Notably, p38 MAPK activation has been implicated in PPARγ signaling. Here, rosiglitazone (RGZ) activation of GPR40 and p38 MAPK was found to boost PPARγ-induced gene transcription in human endothelium. Inhibition or knockdown of p38 MAPK or expression of a dominant negative (DN) p38 MAPK mutant blunted RGZ-induced PPARγ DNA binding and reporter activity in EA.hy926 human endothelial cells. GPR40 inhibition or knockdown, or expression of a DN-Gαq mutant likewise blocked activation of both p38 MAPK and PPARγ reporters. Importantly, RGZ induction of PPARγ target genes in primary human pulmonary artery endothelial cells (PAECs) was suppressed by knockdown of either p38 MAPK or GPR40. GPR40/PPARγ signal transduction was dependent on p38 MAPK activation and induction of PPARγ co-activator-1 (PGC1α). Silencing of p38 MAPK or GPR40 abolished the ability of RGZ to induce phosphorylation and expression of PGC1α in PAECs. Knockdown of PGC1α, its essential activator SIRT1, or its binding partner/co-activator EP300 inhibited RGZ induction of PPARγ-regulated genes in PAECs. RGZ/GPR40/p38 MAPK signaling also led to EP300 phosphorylation, an event that enhances PPARγ target gene transcription. Thus, GPR40 and PPARγ can function as an integrated two-receptor signal transduction pathway, a finding with implications for rational drug development.

Description: A proliferative endothelial cell phenotype, inflammation, and pulmonary vascular remodeling are prominent features of pulmonary arterial hypertension (PAH). Bone morphogenetic protein type II receptor (BMPR2) loss-of-function is the most common cause of heritable PAH and has been closely linked to the formation of pathological plexiform lesions. Although some BMPR2 mutations leave ligand-dependent responses intact, the disruption of ligand-independent, noncanonical functions are universal among PAH-associated BMPR2 genotypes, but incompletely understood. This study examined the noncanonical signaling consequences of BMPR2 silencing in human pulmonary artery endothelial cells to identify potential therapeutic targets. BMPR2 siRNA silencing resulted in a proliferative, promigratory pulmonary artery endothelial cell phenotype and disruption of cytoskeletal architecture. Expression profiling closely reflected these phenotypic changes. Gene set enrichment and promoter analyses, as well as the differential expression of pathway components identified Ras/Raf/ERK signaling as an important consequence of BMPR2 silencing. Raf family members and ERK1/2 were constitutively activated after BMPR2 knockdown. Two Raf inhibitors, sorafenib and AZ628, and low-dose nintedanib, a triple receptor tyrosine kinase inhibitor upstream from Ras, reversed the abnormal proliferation and hypermotility of BMPR2 deficiency. Inhibition of dysregulated Ras/Raf/ERK signaling may be useful in reversing vascular remodeling in PAH.

Description: Glucocorticoids are commonly used to treat inflammatory disorders. The glucocorticoid receptor (GR) can tether to inflammatory transcription factor complexes, such as NFκB and AP-1, and trans-repress the transcription of cytokines, chemokines, and adhesion molecules. In contrast, aldosterone and the mineralocorticoid receptor (MR) primarily promote cardiovascular inflammation by incompletely understood mechanisms. Although MR has been shown to weakly repress NFκB, its role in modulating AP-1 has not been established. Here, the effects of GR and MR on NFκB and AP-1 signaling were directly compared using a variety of ligands, two different AP-1 consensus sequences, GR and MR DNA-binding domain mutants, and siRNA knockdown or overexpression of core AP-1 family members. Both GR and MR repressed an NFκB reporter without influencing p65 or p50 binding to DNA. Likewise, neither GR nor MR affected AP-1 binding, but repression or activation of AP-1 reporters occurred in a ligand-, AP-1 consensus sequence-, and AP-1 family member-specific manner. Notably, aldosterone interactions with both GR and MR demonstrated a potential to activate AP-1. DNA-binding domain mutations that eliminated the ability of GR and MR to cis-activate a hormone response element-driven reporter variably affected the strength and polarity of these responses. Importantly, MR modulation of NFκB and AP-1 signaling was consistent with a trans-mechanism, and AP-1 effects were confirmed for specific gene targets in primary human cells. Steroid nuclear receptor trans-effects on inflammatory signaling are context-dependent and influenced by nuclear receptor conformation, DNA sequence, and the expression of heterologous binding partners. Aldosterone activation of AP-1 may contribute to its proinflammatory effects in the vasculature.

Description: Ultraviolet B radiation (UVBR, 280-315 nm) is known to be a stress factor for Antarctic benthic algae and invertebrates. However, there is almost no available information regarding these effects at the community level. A two-factorial colonization experiment (UVR, three levels and grazing, two levels) was performed at an intertidal and a subtidal site on King George Island/I. 25 de Mayo. Structural parameters of the community were followed for fifteen and ten weeks, respectively. The effects on the intertidal community are presented in detail in Zacher et al. Subtidal communities were dominated macroscopically by colonial diatoms and green algal filaments. Ultraviolet radiation (UVR, 280-400nm) did not affect diatoms but exerted a group-specific effect on the macroalgal assemblage. Overall, red algal cover was negatively impacted by UVR whereas for green algal filaments a significant interaction between grazing and UVR was detected. Grazers introduced a shift in both micro- and macroalgal species composition and reduced the community biomass, with stronger effects when UVBR was absent. When comparing intertidal and subtidal experiments, community architecture and biomass production was markedly different at both sites, with higher biomass and more complex diatom composition at the subtidal spot. However, UVR and grazing affected both sites in a similar pattern. Our findings suggest that UVR and grazing play a key role in shaping the subtidal and intertidal benthic algal communities in Antarctica. UVR impact on subtidal communities seemed to be more complex than in the intertidal, exerting both direct and indirect effects on the community structure.

Description: King George Island (KGI, Isla 25 de Mayo) is located within one of the most rapidly warming regions on Earth at the north-western tip of the Antarctic Peninsula. Since 1991 hydrographical characteristics and phytoplankton dynamics were monitored at two stations in Potter Cove, a fjord-like environment on the south-eastern KGI coastline. Seawater temperature and salinity, total suspended particulate matter (TSPM) and chlorophyll-a (Chl-a, a proxy for phytoplankton biomass) concentrations were measured in summer and winter over a 19 year period, together with local air temperature. Mean air temperatures rose by 0.39 and 0.48 ºC per decade in summer and winter, respectively. Positive anomalies characterised wind speeds during the decade between the mid ’90 and the mid 2000 years, whereas negative anomalies were observed from 2004 onwards. Day of sea ice formation and retreat, based on satellite data, did not change, although total sea ice cover diminished during the studied period. Surface water temperature increased during summer (0.36 ºC per decade), whereas no trend was observed in salinity. Summer Chl-a concentrations were around 1 mg m-3 Chl-a with no clear trend throughout the study period. However, summer Chl-a correlates positively with water column stratification, which in turn resulted from high air temperature and lower salinity in front of the melting glacier. TSPM increased in surface waters of the inner cove during the spring-summer months. The Southern Annular Mode (SAM) climate signal was apparent in the fluctuating interannual pattern of the hydrographic variables in the outer Potter Cove and bottom waters whereas surface hydrography was strongly governed by the local forcing of glacier melt. The results show that global trends have significant effects on local hydrographical and biological conditions in the coastal marine environments of Western Antarctica.