A Chemotactic Peptide from Laminin α5 Functions as a Regulator of Inflammatory Immune Responses via TNFα-mediated Signaling

Abstract

Tissue injury triggers inflammatory responses that may result in release of degradation products or exposure of cryptic domains of extracellular matrix components. Previously, we have shown that a cryptic peptide (AQARSAASKVKVSMKF) in the α-chain of laminin-10 (α5β1γ1), a prominent basement membrane component, is chemotactic for both neutrophils (PMNs) and macrophages (Mφs) and induces matrix metalloproteinase-9 (MMP-9) production. To determine whether AQARSAASKVKVSMKF has additional effects on inflammatory cells, we performed microarray analysis of RNA from RAW264.7 Mφs stimulated with AQARSAASKVKVSMKF. Several cytokines and cytokine receptors were increased >3-fold in response to the laminin α5 peptide. Among these were TNF-α and one of its receptors, the p75 TNFR (TNFR-II), increasing 3.5- and 5.7-fold, respectively. However, the peptide had no effect on p55 TNFR (TNFR-I) expression. Corroborating the microarray data, the protein levels of TNF-α and TNFR-II were increased following stimulation of RAW264.7 cells with AQARSAASKVKVSMKF. In addition, we determined that the production of TNF-α and TNFR-II in response to AQARSAASKVKVSMKF preceded the production of MMP-9. Furthermore, using primary Mφs from mice deficient in TNFR-I, TNFR-II, or both TNF-α receptors (TNFRs), we determined that AQARSAASKVKVSMKF induces MMP-9 expression by Mφs through a pathway triggered by TNFR-II. However, TNF-α signaling is not required for AQARSAASKVKVSMKF-induced PMN release of MMP-9 or PMN emigration. These data suggest that interactions of inflammatory cells with basement membrane components may orchestrate immune responses by inducing expression of cytokines, recruitment of inflammatory cells, and release of proteinases.

A Murine Model of Volumetric Muscle Loss and a Regenerative Medicine Approach for Tissue Replacement

“…Each stage is regulated in part by the temporal expression of well-recognized muscle transcription factors of the basic helix-loop-helix family. 5 However, this regenerative response is critically dependent upon the type and severity of muscle insult. 4 When skeletal muscle injury is more severe and cannot be compensated via inherent regenerative mechanisms, the resulting irrecoverable loss of tissue is referred to as volumetric muscle loss (VML).…”

Regulation of the Immune System by Laminins

“…However, addition of laminin 111 isolated from EHS sarcoma cells to macrophage or monocyte cultures enhances their phagocytic function [84], and upregulates macrophage urokinase-type plasminogen activator and MMP-9 expression [85], mediated by a specific peptide sequence present in laminin α1 and α5 subunits [86]. This cryptic peptide is also chemotactic for neutrophils and macrophages, and increases TNF-α production and TNF receptor expression by macrophages [87]. However, it is not clear whether the laminin α5 sequence that has been shown in vitro to have chemotactic effects is indeed exposed in the intact molecule.…”

MMP generated matrikines

“…A number of laminins have been shown to be cleaved by MMPs, leading to bioactive ECM products. A previous manuscript highlighted that liberation of a specific cryptic epitope of laminin α5 (presumably by proteolytic digestion) releases a 16 amino acid peptide capable of recruiting PMNs and macrophages, along with inducing MMP-9 release from immune cells 67 . More recently, MMP-2 has been shown to cleave laminin-111, liberating a 60kD fragment capable of inducing epithelial-mesenchymal transition in embryonic stem cells 68 .…”