Lysosomal-associated membrane protein-2 plays an important role in the pathogenesis of primary cutaneous vasculitis

Small-molecule α-lipoic acid targets ELK1 to balance human neutrophil and erythrocyte differentiation

BACKGROUND

Erythroid and myeloid differentiation disorders are commonly occurred in leukemia. Given that the relationship between erythroid and myeloid lineages is still unclear. To find the co-regulators in erythroid and myeloid differentiation might help to find new target for therapy of myeloid leukemia. In hematopoiesis, ALA (alpha lipoic acid) is reported to inhibit neutrophil lineage determination by targeting transcription factor ELK1 in granulocyte-monocyte progenitors via splicing factor SF3B1. However, further exploration is needed to determine whether ELK1 is a common regulatory factor for erythroid and myeloid differentiation.

METHODS

In vitro culture of isolated CD34+, CMPs (common myeloid progenitors) and CD34+ CD371- HSPCs (hematopoietic stem progenitor cells) were performed to assay the differentiation potential of monocytes, neutrophils, and erythrocytes. Overexpression lentivirus of long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 transduced CD34+ HSPCs were transplanted into NSG mice to assay the human lymphocyte and myeloid differentiation differences 3 months after transplantation. Knocking down of SRSF11, which was high expressed in CD371+GMPs (granulocyte-monocyte progenitors), upregulated by ALA and binding to ELK1-RNA splicing site, was performed to analyze the function in erythroid differentiation derived from CD34+ CD123mid CD38+ CD371- HPCs (hematopoietic progenitor cells). RNA sequencing of L-ELK1 and S-ELK1 overexpressed CD34+ CD123mid CD38+ CD371- HPCs were performed to assay the signals changed by ELK1.

RESULTS

Here, we presented new evidence that ALA promoted erythroid differentiation by targeting the transcription factor ELK1 in CD34+ CD371- hematopoietic stem progenitor cells (HSPCs). Overexpression of either the long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 inhibited erythroid-cell differentiation, but knockdown of ELK1 did not affect erythroid-cell differentiation. RNAseq analysis of CD34+ CD123mid CD38+ CD371- HPCs showed that L-ELK1 upregulated the expression of genes related to neutrophil activity, phosphorylation, and hypoxia signals, while S-ELK1 mainly regulated hypoxia-related signals. However, most of the genes that were upregulated by L-ELK1 were only moderately upregulated by S-ELK1, which might be due to a lack of serum response factor interaction and regulation domains in S-ELK1 compared to L-ELK1. In summary, the differentiation of neutrophils and erythrocytes might need to rely on the dose of L-ELK1 and S-ELK1 to achieve precise regulation via RNA splicing signals at early lineage commitment.

CONCLUSIONS

ALA and ELK1 are found to regulate both human granulopoiesis and erythropoiesis via RNA spliceosome, and ALA-ELK1 signal might be the target of human leukemia therapy.

Recent topics related to etiology and clinical manifestations of cutaneous arteritis

Cutaneous polyarteritis nodosa (cPAN) was first reported by Lindberg in 1931. It has been recognized as a skin-limited vasculitis whose cutaneous histopathological features are indistinguishable from those of PAN. Cutaneous arteritis (CA) was defined as a form of single-organ vasculitis in the revised Chapel Hill Classification and was recognized as the same disease as cPAN. It became known that deficiency of adenosine deaminase 2 (DADA2) cases were included in cases that had been diagnosed with CA. Because of their similarity and differences in the treatment methods, DADA2 should be considered in CA cases, especially if they are diagnosed or developed in early childhood. Cutaneous arteritis may be classified as an immune complex-mediated vasculitis. It was reported that the pathogenesis of anti-lysosomal-associated membrane protein-2 (LAMP-2) antibodies and anti-phosphatidylserine-prothrombin complex (PS/PT) antibodies as good parameters in CA. The main skin manifestations include livedo racemosa, subcutaneous nodules, and ulcers. Although CA is recognized to have a benign clinical course, it has become known that it is easy to relapse. The existence of skin ulcers upon diagnosis or sensory neuropathies was suggested to be a predictor of poor prognosis. Cutaneous arteritis with them may need to be treated with more intensive therapies.

The Association of Serum Anti-Lysosomal-Associated Membrane Protein-2 Antibody with Vasculitis Combined with Hypertension

The aim of this study was to explore the association of serum anti-lysosomal-associated membrane protein-2 (anti-LAMP-2) antibody with vasculitis combined with hypertension (VAS-HTN). A total of 51 VAS-HTN patients, 46 essential hypertension (EH) patients, and 46 healthy controls (HC) were included in the study. Serum anti-LAMP-2 antibody levels are increased in VAS-HTN patients as compared with EH and HC (all $P<0.05$ ). Serum anti-LAMP-2 antibody levels were significantly higher in active stage patients than those in non-active stage patients and HC (all $P<0.05$ ). The correlation analysis showed a significant positive correlation between serum anti-LAMP-2 antibody levels and the Birmingham Vasculitis Activity Score (BVAS) and hypersensitive C-reactive protein (Hs-CRP) (all $P<0.05$ ). Among the subsets of VAS-HTN, the levels of serum anti-LAMP-2 antibody were remarkably higher in all VAS-HTN subsets compared with HC (all $P<0.05$ ). More interestingly, the levels of serum anti-LAMP-2 antibody were remarkably increased in polyarteritis nodosa (PAN) patients compared with ANCA-associated vasculitis and Takayasu arteritis patients (all $P<0.05$ ). In addition, there was a significant positive correlation between serum anti-LAMP-2 antibody levels and BAVS and Hs-CRP in PAN patients (all $P<0.05$ ). Multivariate logistic regression analysis showed that the anti-LAMP-2 antibody was independently associated with VAS-HTN. The levels of serum anti-LAMP-2 antibody were remarkably increased in VAS-HTN patients compared to EH and HC and might reflect the disease activity. The anti-LAMP-2 antibody may be a potential biomarker for diagnosis and estimating the disease activity in VAS-HTN.

Durvalumab-associated vasculitis presenting as 'the blue toe syndrome'

Durvalumab is a selective, high-affinity human immunoglobulin monoclonal antibody in a class called check point inhibitors, that blocks PD-L1 on tumour cells. Despite clinical success in increasing progression-free survival rates in patients with stage III non-small-cell lung cancer, durvalumab has been associated with immune-related side effects such as pneumonitis and colitis. We present a case of an 84-year-old woman with acral vasculitis presenting as blue toe syndrome, associated with prolonged use of durvalumab. After 1 year of fortnightly durvalumab therapy postchemoradiation therapy, the patient came in with a left blue big toe, and later developed bilateral livedo racemosa. The diagnosis of durvalumab-associated vasculitis was made and treatment with prednisolone was started with clinical improvement.

Biomarkers in Vasculitides of the Nervous System

Besides being affected by the rare and severe primary angiitis of the central nervous system (PACNS) the nervous system is also affected by primary systemic vasculitides (PSV). In contrast to PACNS, PSV affect not only the central but also the peripheral nervous system, resulting in a large array of potential symptoms. Given the high burden of disease, difficulties in distinguishing between differential diagnoses, and incomplete pathophysiological insights, there is an urgent need for additional precise diagnostic tools to enable an earlier diagnosis and initiation of effective treatments. Methods available to date, such as inflammatory markers, antibodies, cerebrospinal fluid (CSF) analysis, imaging, and biopsy, turn out to be insufficient to meet all current challenges. We highlight the use of biomarkers as an approach to extend current knowledge and, ultimately, improve patient management. Biomarkers are considered to be useful for disease diagnosis and monitoring, for predicting response to treatment, and for prognosis in clinical practice, as well as for establishing outcome parameters in clinical trials. In this article, we review the recent literature on biomarkers which have been applied in the context of different types of nervous system vasculitides including PACNS, giant-cell arteritis, Takayasu's arteritis, polyarteritis nodosa, ANCA (anti-neutrophil cytoplasm antibody)-associated vasculitides, cryoglobulinemic vasculitis, IgA vasculitis, and Behçet's disease. Overall, the majority of biomarkers is not specific for vasculitides of the nervous system.

New insights on biomarkers in systemic vasculitis

The systemic vasculitis is a heterogeneous group of diseases characterized by the inflammation of blood vessels. The development of advanced diagnostic tests and genetic studies have resulted in greater improvement in our understanding of vasculitis pathogenesis and thus in the development of newer therapies. However, there is still an unmet need in the management of systemic vasculitis, focused on developing of new biomarkers that would enable distinction between active disease from damage or infection and predict treatment response and prognosis.

Working Intricately with Moh Daha

Moh Daha has been instrumental for initiating and coordinating many European consortia in the area of immunopathogenesis of glomerulonephritis including a number with the author. This review provides a personal history of these developments, ending with INTRICATE, an FP7 medium scale project investigating ANCA-associated vasculitis (AAV). The current status of this research and recent insight in the autoimmune reactions and autoantigens in AAV are briefly summarized.

Emerging concepts in the pathogenesis of antineutrophil cytoplasmic antibody-associated vasculitis

PURPOSE OF REVIEW

Antineutrophil cytoplasmic antibodies (ANCAs) remain central to our current understanding of the pathogenesis of ANCA-associated vasculitis (AAV), and this review considers recent developments in the context of four key questions: are there targets for ANCA beyond myeloperoxidase (MPO) and proteinase 3 (PR3); are all ANCA pathogenic; how are ANCAs generated; and how do ANCA cause disease?

RECENT FINDINGS

B-cell epitope mapping raises the possibility that only a subset of ANCA may be pathogenic. Anti-lysosomal-associated membrane protein 2 autoantibodies have recently emerged as a novel form of ANCA and can be found in anti-MPO and anti-PR3 negative disease. These also provide recent evidence for molecular mimicry in the pathogenesis of AAV, but a definitive proof in human AAV remains elusive. Neutrophil extracellular traps may represent an important mechanism by which MPO and PR3 are taken up by dendritic cells for presentation to the adaptive immune system, and the role of the alternative pathway of complement in AAV has recently been emphasized, with therapeutic implications.

SUMMARY

Our current understanding of the pathogenesis of AAV not only reinforces the central role of neutrophils but also provides a sound rationale for B-cell and complement-directed therapies.

Biomarkers in vasculitis

PURPOSE OF REVIEW

Better biomarkers are needed for guiding management of patients with vasculitis. Large cohorts and technological advances had led to an increase in preclinical studies of potential biomarkers.

RECENT FINDINGS

The most interesting markers described recently include a gene expression signature in CD8+ T cells that predicts tendency to relapse or remain relapse-free in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, and a pair of urinary proteins that are elevated in Kawasaki disease but not other febrile illnesses. Both of these studies used 'omics' technologies to generate and then test hypotheses. More conventional hypothesis-based studies have indicated that the following circulating proteins have potential to improve upon clinically available tests: pentraxin-3 in giant cell arteritis and Takayasu's arteritis; von Willebrand factor antigen in childhood central nervous system vasculitis; eotaxin-3 and other markers related to eosinophils or Th2 immune responses in eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome); and matrix metalloproteinase-3, tissue inhibitor of metalloproteinase-1, and CXCL13 in ANCA-associated vasculitis.

SUMMARY

New markers testable in blood and urine have the potential to assist with diagnosis, staging, assessment of current disease activity, and prognosis. However, the standards for clinical usefulness, in particular, the demonstration of either very high sensitivity or very high specificity have yet to be met for clinically relevant outcomes.

Autoantibodies to hLAMP-2 in ANCA-negative pauci-immune focal necrotizing GN

Pauci-immune focal necrotizing GN (piFNGN) is usually associated with ANCAs that are thought to be pathogenic. However, 10%-15% of patients are ANCA negative and the cause of their injury is unknown. We previously reported a high frequency of autoantibodies to human lysosome-associated membrane protein-2 (hLAMP-2) in ANCA-associated piFNGN, and have now investigated whether the same is true in ANCA-negative patients. Of 11 patients, 8 (73%) had anti-hLAMP-2 antibodies detected by ELISA and confirmed by immunoblotting and indirect immunofluorescence. The autoantibodies from all 8 patients bound to native LAMP-2 purified from human glomeruli and recombinant hLAMP-2 expressed in ldlD cells, both with molecular masses of 110 kD. However, in contrast to anti-LAMP-2 antibodies from ANCA-positive patients, these antibodies from ANCA-negative patients failed to bind the more complexly glycosylated native neutrophil hLAMP-2 (190 kD). Treatment with the deglycosylating enzyme, endo-β-galactosidase, reduced the mass of neutrophil hLAMP-2 to 110 kD and enabled autoantibody binding. Similarly, pretreating neutrophils with endo-β-galactosidase or neuraminidase converted ANCA assay results from negative to positive. Finally, IgG from LAMP-2-positive ANCA-negative patients bound specifically to normal human kidney sections and to human glomerular endothelial cells in culture. In conclusion, in patients with ANCA-negative piFNGN, we have identified autoantibodies to hLAMP-2 that bind native glomerular but not neutrophil hLAMP-2, suggesting a role in pathogenesis.