Mer signaling participates in a novel inhibitory pathway in TLR activation. The purpose of the present study was to examine the role of Mer signaling in the down-regulation of TLR4 activation-driven immune responses in mice, i.t.-treated with LPS, using the specific Mer-blocking antibody. At 4 h and 24 h after LPS treatment, expression of Mer protein in alveolar macrophages and lung tissue decreased, sMer in BALF increased significantly, and Mer activation increased. Pretreatment with anti-Mer antibody did not influence the protein levels of Mer and sMer levels. Anti-Mer antibody significantly reduced LPS-induced Mer activation, phosphorylation of Akt and FAK, STAT1 activation, and expression of SOCS1 and -3. Anti-Mer antibody enhanced LPS-induced inflammatory responses, including activation of the NF-κB pathway; the production of TNF-α, IL-1β, and MIP-2 and MMP-9 activity; and accumulation of inflammatory cells and the total protein levels in BALF. These results indicate that Mer plays as an intrinsic feedback inhibitor of the TLR4- and inflammatory mediator-driven immune responses during acute lung injury.

Mer receptor tyrosine kinase (Mer) signaling plays a central role in the intrinsic inhibition of the inflammatory response to Tolllike receptor activation. Previously, we found that lung Mer protein expression decreased after lipopolysaccharide (LPS) treatment due to enhanced Mer cleavage. The purpose of the present study was to examine whether pharmacologically restored membrane-bound Mer expression upregulates the Mer signaling pathways and suppresses lung inflammatory responses. Pretreatment with the ADAM17 (a disintegrin and metalloproteinase-17) inhibitor TAPI-0 (tumor necrosis factor alpha protease inhibitor-0) reduced LPS-induced production of soluble Mer protein in bronchoalveolar lavage (BAL) fluid, restored membrane-bound Mer expression, and increased Mer activation in alveolar macrophages and lungs after LPS treatment. TAPI-0 also enhanced Mer downstream signaling, including phosphorylation of protein kinase b, focal adhesion kinase, and signal transducer and activator of transcription 1. As expected from enhanced Mer signaling, TAPI-0 also augmented suppressor of cytokine signaling-1 and -3 mRNA and protein levels and inhibited nuclear factor kB activation at 4 and 24 hours after LPS treatment. TAPI-0 suppressed LPS-induced inflammatory cell accumulation, total protein level elevation in BAL fluid, and production of inflammatory mediators, including tumor necrosis factor-a, interleukin-1b, and macrophage inflammatory protein-2. Additionally, the effects of TAPI-0 on the activation of Mer signaling and the production of inflammatory responses could be reversed by cotreatment with specific Merneutralizing antibody. Restored Mer protein expression by treatment with TAPI-0 efficiently prevents the inflammatory cascade during acute lung injury.

Pseudoxanthoma elasticum-like papillary dermal elastolysis is a rare acquired elastolytic disorder characterized by papules that resemble pseudoxanthoma elasticum, and it typically affects elderly women. Histopathological examination shows atrophic epidermis and band-like loss of elastic tissue in the papillary dermis. The pathogenesis is assumed to be related to intrinsic aging because it affects elderly people and shows the loss of elastic tissue. We report a case of pseudoxanthoma elasticum-like papillary dermal elastolysis in early middle age presenting typical clinical and histopathological findings. The patient was a 41-year-old woman who had had her lesions for 10 years. We propose that younger patients, hitherto unknown, can be affected by this disorder and suggest that mechanisms other than intrinsic aging are involved in its pathogenesis.

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