Background and Aims Sterile inflammation is a major clinical concern during ischemia‐reperfusion injury (IRI) triggered by traumatic events, including stroke, myocardial infarction, and solid organ transplantation. Despite high‐mobility group box 1 (HMGB1) clearly being involved in sterile inflammation, its role is controversial because of a paucity of patient‐focused research. Approach and Results Here, we examined the role of HMGB1 oxidation states in human IRI following liver transplantation. Portal blood immediately following allograft reperfusion (liver flush; LF) had increased total HMGB1, but only LF from patients with histopathological IRI had increased disulfide‐HMGB1 and induced Toll‐like receptor 4–dependent tumor necrosis factor alpha production by macrophages. Disulfide HMGB1 levels increased concomitantly with IRI severity. IRI+ prereperfusion biopsies contained macrophages with hyperacetylated, lysosomal disulfide‐HMGB1 that increased postreperfusion at sites of injury, paralleling increased histone acetyltransferase general transcription factor IIIC subunit 4 and decreased histone deacetylase 5 expression. Purified disulfide‐HMGB1 or IRI+ blood stimulated further production of disulfide‐HMGB1 and increased proinflammatory molecule and cytokine expression in macrophages through a positive feedback loop. Conclusions These data identify disulfide‐HMGB1 as a mechanistic biomarker of, and therapeutic target for, minimizing sterile inflammation during human liver IRI.
I F(ab′) 2), macrophages differentiated by endothelium activated with HLA IgG F(ab′) 2 fragment; M(HLA IgG), macrophages differentiated by endothelium activated with intact HLA IgG; TV, transplant vasculopathy.
La-related protein 6 (Larp6) is a conserved RNA-binding protein found across eukaryotes that has been suggested to regulate collagen biogenesis, muscle development, ciliogenesis, and various aspects of cell proliferation and migration. Zebrafish have two Larp6 family genes: larp6a and larp6b. Viable and fertile single and double homozygous larp6a and larp6b zygotic mutants revealed no defects in muscle structure, and were indistinguishable from heterozygous or wild-type siblings. However, larp6a mutant females produced eggs with chorions that failed to elevate fully and were fragile. Eggs from larp6b single mutant females showed minor chorion defects, but chorions from eggs laid by larp6a;larp6b double mutant females were more defective than those from larp6a single mutants. Electron microscopy revealed defective chorionogenesis during oocyte development. Despite this, maternal zygotic single and double mutants were viable and fertile. Mass spectrometry analysis provided a description of chorion protein composition and revealed significant reductions in a subset of zona pellucida and lectin-type proteins between wild-type and mutant chorions that paralleled the severity of the phenotype. We conclude that Larp6 proteins are required for normal oocyte development, chorion formation and egg activation.
Donor-specific HLA Abs contribute to Ab-mediated rejection (AMR) by binding to HLA molecules on endothelial cells (ECs) and triggering intracellular signaling, leading to EC activation and leukocyte recruitment. The molecular mechanisms involving donor-specific HLA Ab–mediated EC activation and leukocyte recruitment remain incompletely understood. In this study, we determined whether TLRs act as coreceptors for HLA class I (HLA I) in ECs. We found that human aortic ECs express TLR3, TLR4, TLR6, and TLR10, but only TLR4 was detected on the EC surface. Consequently, we performed coimmunoprecipitation experiments to examine complex formation between HLA I and TLR4. Stimulation of human ECs with HLA Ab increased the amount of complex formation between HLA I and TLR4. Reciprocal coimmunoprecipitation with a TLR4 Ab confirmed that the crosslinking of HLA I increased complex formation between TLR4 and HLA I. Knockdown of TLR4 or MyD88 with small interfering RNAs inhibited HLA I Ab–stimulated P-selectin expression, von Willebrand factor release, and monocyte recruitment on ECs. Our results show that TLR4 is a novel coreceptor for HLA I to stimulate monocyte recruitment on activated ECs. Taken together with our previous published results, we propose that HLA I molecules form two separate signaling complexes at the EC surface, that is, with TLR4 to upregulate P-selectin surface expression and capture of monocytes to human ECs and integrin β4 to induce mTOR-dependent firm monocyte adhesion via ICAM-1 clustering on ECs, two processes implicated in Ab-mediated rejection.
Background: Cardiac allograft vasculopathy (CAV) is a major cause of late-graft failure and mortality following heart transplantation. The mechanisms underlying vascular remodeling are poorly understood. A major immune risk factor associated with the development of CAV is the presence of donor-specific antibodies (DSA) that induce chronic endothelial cell (EC) injury, leukocyte recruitment and inflammation resulting in thickening of arterial intima. Here, we molecularly characterized innate and adaptive immune cells present in the arteries of rejected cardiac allografts with DSA and identified protein and transcriptomic signatures distinguishing early and late CAV lesions. Methods: Arterial areas of interest (AOIs) from CAV+DSA+ rejected cardiac allografts (N=3; 2 females, 1 male) were subjected to GeoMx digital spatial profiling (DSP). AOIs were scored on the level of CAV progression/neointimal thickening (22 AOIs total; 11 high and 11 low neointima) and were subjected to whole transcriptome and protein profiling. Results: AOIs with low neointima significantly increased markers for activated inflammatory infiltrates, transcripts of EC activation and gene modules involved in activating metalloproteinases and TP53 regulation of caspases. Inflammatory and apoptotic protein markers significantly correlated with inflammatory modules in AOIs with low neointima. AOIs with high neointima increased TGF?-regulated transcripts and modules enriched for platelet activation/aggregation. Proteins encoding SMCs and growth factors/survival correlated with modules enriched for proliferation/repair in AOIs with high neointima. Key transcripts in promoting proliferation, migration, and EndoMT were significantly associated with increasing neointima scores. Conclusion: Our results reveal new protein and transcriptomic signatures associated with CAV progression. Lesions exhibiting inflammatory profiles appear to be early lesions that transition to later proliferative/pro-fibrotic phenotype CAV lesions. These findings should form the foundation for the identification of improved biomarkers to guide CAV treatment.
Cardiac allograft vasculopathy (CAV) is the leading cause of graft failure following heart transplantation. Donor specific antibodies (DSA) contribute to CAV by triggering vessel inflammation and endothelial cell injury. This results in thickening of the arterial intima and vessel occlusion. In this study, we aim to define the innate and adaptive immune cells mediating inflammation and vessel neointima formation using CAV+DSA+ rejected cardiac explants (N=3) and GeoMx digital spatial profiling (DSP). Arterial regions containing macrophages (CD68+CD163+) within vessels (CD34+) were selected for whole genome sequencing and a 76-protein panel. Arteries were scored as containing ‘low’ or ‘high’ neointima based on H&E. A total of 41 proteins including markers of inflammation and apoptosis were found to be expressed in all arteries. The expression of CD8, CD56, CD20, CD127, and CD11c exhibited a significantly positive correlation with RNA counterparts. A total of 15 differentially expressed proteins (e.g., T-cell makers: CD8, CD45RO, and CD127), and high expression of genes related to inflammation (ITGAX), and apoptosis (TP63), along with pathways for antigen presentation were elevated in arteries with low neointima. High neointima arteries showed higher SMA protein expression and increased genes related to cell growth (LECT2), complement regulation (CFHR3) and anti-inflammatory factors (FNDC4). Enriched pathways in high neointimal arteries included platelet activation/degranulation and cell migration. Our results provide insight into the mechanisms mediating CAV progression seen by inflammatory profiles in arteries with low neointima followed by pro-fibrotic/reparative phenotypes in high neointima arteries. This work is funded by the Ruth L. Kirschstein National Research Service Award (NRSA) T32HL069766 (UCLA Vascular Biology Training grant), the Eugene V. Cota Robles Fellowship and NIH Grant 441450 ER 29762
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