Homeostatic, Non-Canonical Role of Macrophage Elastase in Vascular Integrity.

BACKGROUND: Matrix metalloproteinase (MMP)-12 is highly expressed in abdominal aortic aneurysms and its elastolytic function has been implicated in the pathogenesis. This concept is challenged, however, by conflicting data. Here, we sought to revisit the role of MMP-12 in abdominal aortic aneurysm. METHODS: Apoe-/- and Mmp12-/-/Apoe-/- mice were infused with Ang II (angiotensin). Expression of neutrophil extracellular traps (NETs) markers and complement component 3 (C3) levels were evaluated by immunostaining in aortas of surviving animals. Plasma complement components were analyzed by immunoassay. The effects of a complement inhibitor, IgG-FH1-5 (factor H-immunoglobulin G), and macrophage-specific MMP-12 deficiency on adverse aortic remodeling and death from rupture in Ang II-infused mice were determined. RESULTS: Unexpectedly, death from aortic rupture was significantly higher in Mmp12-/-/Apoe-/- mice. This associated with more neutrophils, citrullinated histone H3 and neutrophil elastase, markers of NETs, and C3 levels in Mmp12-/- aortas. These findings were recapitulated in additional models of abdominal aortic aneurysm. MMP-12 deficiency also led to more pronounced elastic laminae degradation and reduced collagen integrity. Higher plasma C5a in Mmp12-/- mice pointed to complement overactivation. Treatment with IgG-FH1-5 decreased aortic wall NETosis and reduced adverse aortic remodeling and death from rupture in Ang II-infused Mmp12-/- mice. Finally, macrophage-specific MMP-12 deficiency recapitulated the effects of global MMP-12 deficiency on complement deposition and NETosis, as well as adverse aortic remodeling and death from rupture in Ang II-infused mice. CONCLUSIONS: An MMP-12 deficiency/complement activation/NETosis pathway compromises aortic integrity, which predisposes to adverse vascular remodeling and abdominal aortic aneurysm rupture. Considering these new findings, the role of macrophage MMP-12 in vascular homeostasis demands re-evaluation of MMP-12 function in diverse settings.

Producing amyloid fibrils in vitro: A tool for studying AL amyloidosis.

Amyloid light-chain (AL) amyloidosis is the second most common form of systemic amyloidosis which is characterized by a high level of mortality and no effective treatment to remove fibril deposition. This disorder is caused by malfunctioning of B-cells resulting in production of abnormal protein fibrils composed of immunoglobulin light chain fragments that tend to deposit on various organs and tissues. AL amyloidosis is set apart from other forms of amyloidosis in that no specific sequences have been identified in the immunoglobulin light chains that are amyloid fibril formation causative and patient specific. This unusual feature hinders the therapeutic progress and requires either direct access to patient samples (which is not always possible) or a source of in vitro produced fibrils. While isolated reports of successful AL amyloid fibril formation from various patient-specific protein sequences can be found in literature, no systematic research on this topic was performed since 1999. In the present study we have developed a generalized approach to in vitro fibril production from various types of previously reported [[1], [2], [3]] amyloidogenic immunoglobulin light chains and their fragments. We describe the procedure from selection and generation of starting material, through finding of optimal assay conditions, to applying a panel of methods to confirm successful fibril formation. Procedure details are discussed in the light of the most recent findings and theories on amyloid fibril formation. The reported protocol produces high quality AL amyloid fibrils that can subsequently be used in the development of the much-needed amyloid-targeting diagnostic and therapeutic approaches.