Tim4 recognizes carbon nanotubes and mediates phagocytosis leading to granuloma formation.

Macrophage recognition and phagocytosis of crystals is critical for the associated fibrosis and cancer. Of note, multi-walled carbon nanotubes (MWCNTs), the highly representative products of nanotechnology, induce macrophage NLRP3 inflammasome activation and cause asbestosis-like pathogenesis. However, it remains largely unknown how macrophages efficiently recognize MWCNTs on their cell surfaces. Here, we identify by a targeted screening of phagocyte receptors the phosphatidylserine receptors T cell immunoglobulin mucin 4 (Tim4) and Tim1 as the pattern-recognition receptors for carbon crystals. Docking simulation studies reveal spatiotemporally stable interfaces between aromatic residues in the extracellular IgV domain of Tim4 and one-dimensional carbon crystals. Further, CRISPR-Cas9-mediated deletion of Tim4 and Tim1 reveals that Tim4, but not Tim1, critically contributes to the recognition of MWCNTs by peritoneal macrophages and to granuloma development in a mouse model of direct mesothelium exposure to MWCNTs. These results suggest that Tim4 recognizes MWCNTs through aromatic interactions and mediates phagocytosis leading to granulomas.

A hypomorphic variant in EYS detected by genome-wide association study contributes toward retinitis pigmentosa.

The genetic basis of Japanese autosomal recessive retinitis pigmentosa (ARRP) remains largely unknown. Herein, we applied a 2-step genome-wide association study (GWAS) in 640 Japanese patients. Meta-GWAS identified three independent peaks at P < 5.0 × 10-8, all within the major ARRP gene EYS. Two of the three were each in linkage disequilibrium with a different low frequency variant (allele frequency < 0.05); a known founder Mendelian mutation (c.4957dupA, p.S1653Kfs*2) and a non-synonymous variant (c.2528 G > A, p.G843E) of unknown significance. mRNA harboring c.2528 G > A failed to restore rhodopsin mislocalization induced by morpholino-mediated knockdown of eys in zebrafish, consistent with the variant being pathogenic. c.2528 G > A solved an additional 7.0% of Japanese ARRP cases. The third peak was in linkage disequilibrium with a common non-synonymous variant (c.7666 A > T, p.S2556C), possibly representing an unreported disease-susceptibility signal. GWAS successfully unraveled genetic causes of a rare monogenic disorder and identified a high frequency variant potentially linked to development of local genome therapeutics.

SiO2 and TiO2 nanoparticles synergistically trigger macrophage inflammatory responses.

Silicon dioxide (SiO2) nanoparticles (NPs) and titanium dioxide (TiO2) NPs are the most widely used inorganic nanomaterials. Although the individual toxicities of SiO2 and TiO2 NPs have been extensively studied, the combined toxicity of these NPs is much less understood. In this study, we observed unexpected and drastic activation of the caspase-1 inflammasome and production of IL-1ß in mouse bone marrow-derived macrophages stimulated simultaneously with SiO2 and TiO2 NPs at concentrations at which these NPs individually do not cause macrophage activation. Consistent with this, marked lung inflammation was observed in mice treated intratracheally with both SiO2 and TiO2 NPs. In macrophages, SiO2 NPs localized in lysosomes and TiO2 NPs did not; while only TiO2 NPs produced ROS, suggesting that these NPs induce distinct cellular damage leading to caspase-1 inflammasome activation. Intriguingly, dynamic light scattering measurements revealed that, although individual SiO2 and TiO2 NPs immediately aggregated to be micrometer size, the mixture of these NPs formed a stable and relatively monodisperse complex with a size of ~250 nm in the presence of divalent cations. Taken together, these results suggest that SiO2 and TiO2 NPs synergistically induce macrophage inflammatory responses and subsequent lung inflammation. Thus, we propose that it is important to assess the synergistic toxicity of various combinations of nanomaterials.

SR-B1 Is a Silica Receptor that Mediates Canonical Inflammasome Activation.

The inhalation of silica dust is associated with fibrosis and lung cancer, which are triggered by macrophage inflammatory responses; however, how macrophages recognize silica remains largely unknown. Here, we identify by functional expression cloning the class B scavenger receptor SR-B1 as a silica receptor. Through an extracellular α-helix, both mouse and human SR-B1 specifically recognized amorphous and crystalline silica, but not titanium dioxide nanoparticles, latex nanoparticles, or monosodium urate crystals, although all particles exhibited negative surface potentials. Genetic deletion of SR-B1 and masking of SR-B1 by monoclonal antibodies showed that SR-B1-mediated recognition of silica is associated with caspase-1-mediated inflammatory responses in mouse macrophages and human peripheral blood monocytes. Furthermore, SR-B1 was involved in silica-induced pulmonary inflammation in mice. These results indicate that SR-B1 is a silica receptor associated with canonical inflammasome activation.