Partial Netrin-1 Deficiency Aggravates Acute Kidney Injury

The netrin family of secreted proteins provides migrational cues in the developing central nervous system. Recently, netrins have also been shown to regulate diverse processes beyond their functions in the brain, incluing the ochrestration of inflammatory events. Particularly netrin-1 has been implicated in dampening hypoxia-induced inflammation. Here, we hypothesized an anti-inflammatory role of endogenous netrin-1 in acute kidney injury (AKI). As homozygous deletion of netrin-1 is lethal, we studied mice with partial netrin-1 deletion (Ntn-1+/− mice) as a genetic model. In fact, Ntn-1+/− mice showed attenuated Ntn-1 levels at baseline and following ischemic AKI. Functional studies of AKI induced by 30 min of renal ischemia and reperfusion revealed enhanced kidney dysfunction in Ntn-1+/− mice as assessed by measurements of glomerular filtration, urine flow rate, urine electrolytes, serum creatinine and creatinine clearance. Consistent with these findings, histological studies indicated a more severe degree kidney injury. Similarly, elevations of renal and systemic inflammatory markers were enhanced in mice with partial netrin-1 deficiency. Finally, treatment of Ntn-1+/− mice with exogenous netrin-1 restored a normal phenotype during AKI. Taking together, these studies implicate endogenous netrin-1 in attenuating renal inflammation during AKI

Rtp801 Suppression of Epithelial mTORC1 Augments Endotoxin-Induced Lung Inflammation

The mechanistic target of rapamycin (mTOR) is a central regulator of cellular responses to environmental stress. mTOR (and its primary complex mTORC1) is, therefore, ideally positioned to regulate lung inflammatory responses to an environmental insult, a function directly relevant to disease states such as the acute respiratory distress syndrome. Our previous work in cigarette smoke-induced emphysema identified a novel protective role of pulmonary mTORC1 signaling. However, studies of the impact of mTORC1 on the development of acute lung injury are conflicting. We hypothesized that Rtp801, an endogenous inhibitor of mTORC1, which is predominantly expressed in alveolar type II epithelial cells, is activated during endotoxin-induced lung injury and functions to suppress anti-inflammatory epithelial mTORC1 responses. We administered intratracheal lipopolysaccharide to wild-type mice and observed a significant increase in lung Rtp801 mRNA. In lipopolysaccharide-treated Rtp801(-/-) mice, epithelial mTORC1 activation significantly increased and was associated with an attenuation of lung inflammation. We reversed the anti-inflammatory phenotype of Rtp801(-/-) mice with the mTORC1 inhibitor, rapamycin, reassuring against mTORC1-independent effects of Rtp801. We confirmed the proinflammatory effects of Rtp801 by generating a transgenic Rtp801 overexpressing mouse, which displayed augmented inflammatory responses to intratracheal endotoxin. These data suggest that epithelial mTORC1 activity plays a protective role against lung injury, and its inhibition by Rtp801 exacerbates alveolar injury caused by endotoxin

Immunoglobulin-driven complement activation regulates pro-inflammatory remodeling in pulmonary hypertension.

RATIONALE: Pulmonary (arterial) hypertension (PH/PAH) is a life-threatening cardiopulmonary disorder where inflammation and immunity have emerged as critical early pathogenic elements. Although pro-inflammatory processes in PH/PAH are the focus of extensive investigation, the initiating mechanisms remain elusive. OBJECTIVES: We tested whether activation of the complement cascade is critical in regulating pro-inflammatory and pro-proliferative processes in the initiation of experimental hypoxic PH, and can serve as a prognostic biomarker of outcome in human PAH. METHODS: We employed immunostaining of lung tissues from experimental PH models and PAH patients; analyses of genetic murine models lacking specific complement components or circulating immunoglobulins; cultured human pulmonary adventitial fibroblasts; and network medicine analysis of a biomarker risk panel from plasma of PAH patients. MEASUREMENTS AND MAIN RESULTS: Pulmonary perivascular-specific activation of the complement cascade was identified as a consistent critical determinant of PH/PAH in experimental animal models and humans. In experimental hypoxic PH, pro-inflammatory and pro-proliferative responses were complement (Alternative pathway and C5)-dependent, and immunoglobulins, particularly IgG, were critical for activation of the complement cascade. We identify Csf2/GM-CSF as a primary complement-dependent inflammatory mediator. Furthermore, using network medicine analysis of a biomarker risk panel from plasma of PAH patients, we demonstrate that complement signaling can serve as a prognostic factor for clinical outcome in PAH. CONCLUSIONS: The present study establishes immunoglobulin-driven dysregulated complement activation as a critical pathobiological mechanism regulating pro-inflammatory/pro-proliferative processes in the initiation of experimental hypoxic PH, and demonstrates complement signaling as a critical determinant of clinical outcome of in PAH

Modern Age Pathology of Pulmonary Arterial Hypertension

Rationale: The impact of modern treatments of pulmonary arterial hypertension (PAH) on pulmonary vascular pathology remains unknown. Objectives: To assess the spectrum of pulmonary vascular remodeling in the modern era of PAH medication. Methods: Assessment of pulmonary vascular remodeling and inflammation in 62 PAH and 28 control explanted lungs systematically sampled. Measurements and Main Results: Intima and intima plus media fractional thicknesses of pulmonary arteries were increased in the PAH group versus the control lungs and correlated with pulmonary hemodynamic measurements. Despite a high variability of morphological measurements within a given PAH lung and among all PAH lungs, distinct pathological subphenotypes were detected in cohorts of PAH lungs. These included a subset of lungs lacking intima or, most prominently, media remodeling, which had similar numbers of profiles of plexiform lesions as those in lungs with more pronounced remodeling. Marked perivascular inflammation was present in a high number of PAH lungs and correlated with intima plus media remodeling. The number of profiles of plexiform lesions was significantly lower in lungs of male patients and those never treated with prostacyclin or its analogs. Conclusions: Our results indicate that multiple features of pulmonary vascular remodeling are present in patients treated with modern PAH therapies. Perivascular inflammation may have an important role in the processes of vascular remodeling, all of which may ultimately lead to increased pulmonary artery pressure. Moreover, our study provides a framework to interpret and design translational studies in PAH

Hypoxia-Inducible Factor 1α Signaling Promotes Repair of the Alveolar Epithelium after Acute Lung Injury

During the acute respiratory distress syndrome, epithelial cells, primarily alveolar type (AT) I cells, die and slough off, resulting in enhanced permeability. ATII cells proliferate and spread onto the denuded basement membrane to reseal the barrier. Repair of the alveolar epithelium is critical for clinical recovery; however, mechanisms underlying ATII cell proliferation and spreading are not well understood. We hypothesized that hypoxia-inducible factor (HIF)1α promotes proliferation and spreading of ATII cells during repair after lung injury. Mice were treated with lipopolysaccharide or hydrochloric acid. HIF activation in ATII cells after injury was demonstrated by increased luciferase activity in oxygen degradation domain-Luc (HIF reporter) mice and expression of the HIF1α target gene GLUT1. ATII cell proliferation during repair was attenuated in ATII cell-specific HIF1α knockout (SftpcCreERT2+/-;HIF1αf/f) mice. The HIF target vascular endothelial growth factor promoted ATII cell proliferation in vitro and after lung injury in vivo. In the scratch wound assay of cell spreading, HIF stabilization accelerated, whereas HIF1α shRNA delayed wound closure. SDF1 and its receptor, CXCR4, were found to be HIF1α-regulated genes in ATII cells and were up-regulated during lung injury. Stromal cell-derived factor 1/CXCR4 inhibition impaired cell spreading and delayed the resolution of permeability after lung injury. We conclude that HIF1α is activated in ATII cells after lung injury and promotes proliferation and spreading during repair