Resolvin D1 promotes the targeting and clearance of necroptotic cells

Abstract

Inflammation-resolution is a protective response that is mediated by specialized pro-resolving mediators (SPMs). The clearance of dead cells or efferocytosis is a critical cellular program of inflammation-resolution. Impaired efferocytosis can lead to tissue damage in prevalent human diseases, like atherosclerosis. Therefore understanding mechanisms associated with swift clearance of dead cells is of utmost clinical importance. Recently, the accumulation of necroptotic cells (NCs) was observed in human plaques and we postulated that this is due to defective clearance programs. Here we present evidence that NCs are inefficiently taken up by macrophages because they have increased surface expression of a well-known "don't eat me" signal called CD47. High levels of CD47 on NCs stimulated RhoA-pMLC signaling in macrophages that promoted "nibbling", rather than whole-cell engulfment of NCs. Anti-CD47 blocking antibodies limited RhoA-p-MLC signaling and promoted whole-cell NC engulfment. Treatment with anti-CD47 blocking antibodies to Ldlr −/− mice with established atherosclerosis decreased necrotic cores, limited the accumulation of plaque NCs and increased lesional SPMs, including Resolvin D1 (RvD1) compared with IgG controls. Mechanistically, RvD1 promoted whole-cell engulfment of NCs by decreasing RhoA signaling and activating CDC42. RvD1 specifically targeted NCs for engulfment by facilitating the release of the well-known "eat me signal" called calreticulin from macrophages in a CDC42 dependent manner. Lastly, RvD1 enhanced the clearance of NCs in advanced murine plaques. Together, these results suggest new molecules and signaling associated with the clearance of NCs, provide a new paradigm for the regulation of inflammation-resolution, and offer a potential treatment strategy for diseases where NCs underpin the pathology.

Carcinogenesis: Failure of resolution of inflammation?

“…Hepatocellular carcinoma ensues in the presence of excessive hepatic apoptosis and necroptosis in the tumor microenvironment which directs lineage commitment to either hepatocellular carcinoma or intrahepatic cholangiocarcinoma ( Seehawer et al, 2018 ). The clearance of necroptotic cells are inefficiently taken up by macrophages in diseases characterized by impaired inflammation resolution ( Gerlach et al, 2020 ) . Necroptotic cells are inefficiently taken up by macrophages because they have increased surface expression of CD47, a “don't eat me” signal ( Gerlach et al, 2020 ).…”

“…The clearance of necroptotic cells are inefficiently taken up by macrophages in diseases characterized by impaired inflammation resolution ( Gerlach et al, 2020 ) . Necroptotic cells are inefficiently taken up by macrophages because they have increased surface expression of CD47, a “don't eat me” signal ( Gerlach et al, 2020 ). Resolvin D1 enhanced the clearance of necroptotic cells in advanced murine plaques by the release of the “eat me signal” calreticulin from macrophages in a CDC42 dependent manner ( Gerlach et al, 2020 ) .…”

Calreticulin Blockade Attenuates Murine Acute Lung Injury by Inducing Polarization of M2 Subtype Macrophages

“…A body of evidences showed that CALR is highly expressed in tumor cells and transported onto cell membrane to serve as a C1q receptor and prophagocytic signal for macrophage phagocytosis of cancer cells and dead cells (12,13). Because the exposed CALR can be released into extracellular milieu (14,15), the serum CALR is highly elevated in the tumor patients and positively correlated to the prognosis of tumor (16,17). Therefore, serum CALR is considered as a useful biomarker in cancer diagnosis and prognosis evaluation.…”

Necroptosis in Immuno-Oncology and Cancer Immunotherapy

“…However, the critical evidence supporting exposure of surface calreticulin (CALR) by necroptotic cells is largely absent. Moreover, CD47, a well-known "do not eat me" signal, has been found to modulate phagocytic clearance of necroptotic cells [157,159]. Irrespective of these observations, it is generally accepted that the uptake of necroptotic cells might not be as proficient as that of apoptotic cells [156][157][158][159], although an opposite scenario in which necroptotic cells were efferocytosed more efficiently, has also been proposed [137].…”