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Biomedical subjects

William J Janssen

Publications and source records attributed to William J Janssen.

12 recordsLinked to original sources
PubMed2026

Human airspace macrophage signatures are conserved during sterile lung injury and repair.

RATIONALE: Airspace macrophages (AM) are implicated in both persistent inflammation and tissue repair following acute lung injury. Distinct subsets of AM are associated with lung pathology in humans but whether unique AM signatures are specific to disease states or represent a conserved response to lung inflammation is unknown. OBJECTIVES: We sought to test the hypothesis that conserved subsets of inflammatory and reparative AM could be identified by transcriptional programing in a human model of self-resolving acute lung injury. METHODS: Fifteen subjects underwent bronchoscopic lavage (BAL) before and at a pre-assigned time point after endobronchial exposure to bacterial endotoxin. BAL cells were subjected to single cell RNA sequencing and longitudinal assessment of AM programing during resolution of inflammation and lung repair was performed. MEASUREMENTS AND MAIN RESULTS: We identify transcriptionally distinct subsets of tissue resident and recruited AM present at all time points, in all subjects. Two recruited AM populations increase following inflammation, one which aligns with classical monocytes (MoAM) and one with interstitial macrophages (IAM). AM subsets display unique patterns of gene expression throughout the time course. Comparison of subset-specific markers to those identified in disease states reveals that IAM express many so-called "pathogenic" markers during normal lung repair. CONCLUSIONS: By applying a uniform inflammatory stimulus to healthy adults and examining BAL cells obtained at precise time points thereafter, we construct a time-resolved kinetic of AM transcriptional programing during typical lung repair. Our data demonstrate that IAM share transcriptional similarity to AM identified in disease states and suggest they may reflect a conserved cellular response to tissue injury.

Journal Article↗
PubMed2026

Alternative splicing of toll-like receptor pathway mRNAs in lung immune cells from patients with ARDS.

Acute respiratory distress syndrome (ARDS) is characterized by robust inflammation in the lungs and systemic circulation. In this context, the toll-like receptor (TLR) signaling pathway plays a major role, driving inflammation that promotes host defense but also causing pathological tissue damage. To limit excessive inflammation, TLR signaling must be tightly controlled. One mechanism that modulates TLR signaling is alternative splicing of TLR pathway pre-mRNAs, which balances production of positively acting inflammatory mediators with alternative splice forms that terminate inflammation. To determine whether altered TLR pathway splicing contributes to pathological inflammation in ARDS, we evaluated two central mediators of the TLR signaling pathway, the MyD88 signaling adapter and the IRAK1 signaling kinase, in leukocytes isolated from bronchoalveolar lavage (BAL) of patients with ARDS. We found that MyD88 gene expression was decreased in BAL immune cells, whereas IRAK1 gene expression was increased. In parallel, we monitored long proinflammatory (MyD88-L and IRAK1) and shorter anti-inflammatory (MyD88-S and IRAK1c) splice forms and determined that IRAK1 splicing was shifted in a proinflammatory direction in patients with ARDS. Finally, we evaluated relationships between MyD88 isoform levels in BAL leukocytes and clinical outcomes. We conclude that pre-mRNA splicing of TLR pathway genes is altered in lung immune cells in patients with ARDS, that monitoring splicing of these genes may provide important prognostic information, and that manipulating splicing of these genes may be a useful novel therapeutic approach that needs further investigation.NEW & NOTEWORTHY We found that MyD88 expression is decreased, that IRAK1 expression is increased, and that IRAK1 splicing is shifted in a proinflammatory direction, in lung immune cells in patients with ARDS. We also find that MyD88 expression levels may correlate with survival in patients with ARDS. Thus, changes in expression and splicing of these two genes offer potential novel prognostic and therapeutic targets for ARDS.

Humans↗
PubMed2006

ATP-binding cassette transporter A7 enhances phagocytosis of apoptotic cells and associated ERK signaling in macrophages.

The mammalian ATP-binding cassette transporters A1 and A7 (ABCA1 and -A7) show sequence similarity to CED-7, a Caenorhabditis elegans gene that mediates the clearance of apoptotic cells. Using RNA interference or gene targeting, we show that knock down of macrophage ABCA7 but not -A1 results in defective engulfment of apoptotic cells. In response to apoptotic cells, ABCA7 moves to the macrophage cell surface and colocalizes with the low-density lipoprotein receptor-related protein 1 (LRP1) in phagocytic cups. The cell surface localization of ABCA7 and LRP1 is defective in ABCA7-deficient cells. C1q is an opsonin of apoptotic cells that acts via phagocyte LRP1 to induce extracellular signal-regulated kinase (ERK) signaling. We show that ERK signaling is required for phagocytosis of apoptotic cells and that ERK phosphorylation in response to apoptotic cells or C1q is defective in ABCA7-deficient cells. These studies reveal a major role of ABCA7 and not -A1 in the clearance of apoptotic cells and therefore suggest that ABCA7 is an authentic orthologue of CED-7.

ATP Binding Cassette Transporter 1↗
PubMed2006

Lovastatin enhances clearance of apoptotic cells (efferocytosis) with implications for chronic obstructive pulmonary disease.

Statins are potent, cholesterol-lowering agents with newly appreciated, broad anti-inflammatory properties, largely based upon their ability to block the prenylation of Rho GTPases, including RhoA. Because phagocytosis of apoptotic cells (efferocytosis) is a pivotal regulator of inflammation, which is inhibited by RhoA, we sought to determine whether statins enhanced efferocytosis. The effect of lovastatin on efferocytosis was investigated in primary human macrophages, in the murine lung, and in human alveolar macrophages taken from patients with chronic obstructive pulmonary disease. In this study, we show that lovastatin increased efferocytosis in vitro in an 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase-dependent manner. Lovastatin acted by inhibiting both geranylgeranylation and farnesylation, and not by altering expression of key uptake receptors or by increasing binding of apoptotic cells to phagocytes. Lovastatin appeared to exert its positive effect on efferocytosis by inhibiting RhoA, because it 1) decreased membrane localization of RhoA, to a greater extent than Rac-1, and 2) prevented impaired efferocytosis by lysophosphatidic acid, a potent inducer of RhoA. Finally, lovastatin increased efferocytosis in the naive murine lung and ex vivo in chronic obstructive pulmonary disease alveolar macrophages in an HMG-CoA reductase-dependent manner. These findings indicate that statins enhance efferocytosis in vitro and in vivo, and suggest that they may play an important therapeutic role in diseases where efferocytosis is impaired and inflammation is dysregulated.

Animals↗
PubMed2006

Oxidants selectively reverse TGF-beta suppression of proinflammatory mediator production.

Although TGF-beta inhibits the production of proinflammatory mediators in vitro and in vivo, its anti-inflammatory activities may be ineffective in early or severe acute inflammatory circumstances. In this study, we suggest a role for oxidative stress on TGF-beta signaling, leading to prevention of its normal anti-inflammatory effects but leaving its Smad-driven effects on cellular differentiation or matrix production unaffected. Stimulation of the RAW 264.7 macrophage cells, human or mouse alveolar macrophages with LPS led to NF-kappaB-driven production of proinflammatory mediators, which were inhibited by TGF-beta. This inhibition was prevented in the presence of hydrogen peroxide. We found that hydrogen peroxide acted by inducing p38 MAPK activation, which then prevented the ERK activation and MAPK phosphatase-1 up-regulation normally induced by TGF-beta. This was mediated through Src tyrosine kinases and protein phosphatase-1/2A. By contrast, hydrogen peroxide had no effects on TGF-beta-induced Smad2 phosphorylation and SBE-luc reporter gene transcription.

Animals↗
PubMed2005

Cell-surface calreticulin initiates clearance of viable or apoptotic cells through trans-activation of LRP on the phagocyte.

Apoptotic-cell removal is critical for development, tissue homeostasis, and resolution of inflammation. Although many candidate systems exist, only phosphatidylserine has been identified as a general recognition ligand on apoptotic cells. We demonstrate here that calreticulin acts as a second general recognition ligand by binding and activating LDL-receptor-related protein (LRP) on the engulfing cell. Since surface calreticulin is also found on viable cells, a mechanism preventing inadvertent uptake was sought. Disruption of interactions between CD47 (integrin-associated protein) on the target cell and SIRPalpha (SHPS-1), a heavily glycosylated transmembrane protein on the engulfing cell, permitted uptake of viable cells in a calreticulin/LRP-dependent manner. On apoptotic cells, CD47 was altered and/or lost and no longer activated SIRPalpha. These changes on the apoptotic cell create an environment where "don't eat me" signals are rendered inactive and "eat me" signals, including calreticulin and phosphatidylserine, congregate together and signal for removal.

Animals↗