Collagen inhibits phagocytosis of amyloid in vitro and in vivo and may act as a ‘don’t eat me’ signal

Abstract

Background

Systemic amyloidosis refers to a group of protein misfolding disorders characterized by the extracellular deposition of amyloid fibrils in organs and tissues. For reasons heretofore unknown, amyloid deposits are not recognized by the immune system, and progressive deposition leads to organ dysfunction.

Methods

In vitro and in vivo phagocytosis assays were performed to elucidate the impact of collagen and other amyloid associated proteins (eg serum amyloid p component and apolipoprotein E) had on amyloid phagocytosis. Immunohistochemical and histopathological staining regimens were employed to analyze collagen-amyloid interactions and immune responses.

Results

Histological analysis of amyloid-laden tissue indicated that collagen is intimately associated with amyloid deposits. We report that collagen inhibits phagocytosis of amyloid fibrils by macrophages. Treatment of 15 patient-derived amyloid extracts with collagenase significantly enhanced amyloid phagocytosis. Preclinical mouse studies indicated that collagenase treatment of amyloid extracts significantly enhanced clearance as compared to controls, coincident with increased immune cell infiltration of the subcutaneous amyloid lesion.

Conclusions

These data suggest that amyloid-associated collagen serves as a ‘don’t eat me’ signal, thereby hindering clearance of amyloid. Targeted degradation of amyloid-associated collagen could result in innate immune cell recognition and clearance of pathologic amyloid deposits.

Keywords:

• AL amyloidosis
• amyloid clearance
• amyloid phagocytosis
• ATTR amyloidosis
• collagen

Acknowledgements

We thank Jim Wesley for tissue processing, slide preparation and performing the Masson-Trichrome histological stain. This work was supported by internal funds provided by the University of Tennessee Graduate School of Medicine.

Author contributions

JWJ, JSF, EBM, SM, CW, MB, TR and ADM performed the experiments; REH performed statistical analyses; JWJ, JSF, SJK and JSW wrote, revised and finalized the manuscript; JWJ, JSF and JSW designed the studies; JWJ, EBM, REH and JSW analyzed data; and JWJ and JSF share co–first authorship for equal contributions to the design and execution of the studies.

Disclosure statement

EBM, TR and SJK are founders and shareholders, and JSW is interim CSO, founder and shareholder of Attralus Inc.

Additional information

Funding

This work was supported by Univeristy of Tennessee Graduate School of Medicine Gift Fund.