Mactinin, a fragment of cytoskeletal alpha-actinin, is a novel inducer of heat shock protein (Hsp)-90 mediated monocyte activation

New insights into fibrosis from the ECM degradation perspective: the macrophage-MMP-ECM interaction

Fibrosis is a pathological feature of a variety of chronic inflammatory diseases that can affect almost all organs, which can cause severe consequences and even lead to death. Fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) due to disruption of the balance between ECM production and degradation. Although overabundance of ECM proteins has long been the focus of studies on fibrosis, another facet of the problem—impaired degradation of the ECM—is gaining increasing attention. Matrix metalloproteinase (MMP) and the tissue inhibitor of metalloproteinase (TIMP) system is the main molecular system contributing to ECM degradation, and macrophages are the major regulators of ECM. However, the relationship among macrophages, the MMP/TIMP system and the ECM is not fully understood in the context of fibrosis. Here, we discuss in detail the role played by the ECM in the development of fibrosis and highlight the macrophage-MMP-ECM interaction that is involved in fibrogenesis and may be a potential therapeutic target for fibrosis.

Changes in the levels of α-actinin-4 in differentiating human myeloid leukemia cells induced by retinoic acid

Retinoic acid (RA) induces granulocytic differentiation and inhibits the growth of human promyelocytic leukemia HL60 cells. α-Actinin-4 is a member of the α-actinin family, which exhibits unique mechanosensory regulation. Herein, we elucidated the effects of RA on α-actinin-4 expression during cell differentiation. RA increased the levels of α-actinin-4 protein significantly, while mRNA expression remained unchanged. In addition, RA treatment altered the intracellular localization of α-actinin-4 from the nucleus to the cytoplasm. Cells pretreated with RA, maintained α-actinin-4 protein levels after cycloheximide treatment as compared with control cells. The amount of ubiquitylated α-actinin-4 protein in RA-treated cells was less than in control cells. These results indicate that RA may inhibit nuclei transport and proteasomal degradation of α-actinin-4 protein. α-Actinin-4 may play a significant role in RA-induced differentiation, including the promotion of cytomorphology changes.

Involvement of cell surface 90 kDa heat shock protein (HSP90) in pattern recognition by human monocyte-derived macrophages

Heat shock proteins (HSPs) are typical intracellular chaperones which also appear on the cell surface and in extracellular milieu. HSP90, which chaperones many proteins involved in signal transduction, is also a regular component of LPS-signaling complexes on Mϕ. As LPS is a prototypical PAMP, we speculated that HSP90 is engaged in pattern recognition by professional phagocytes. In this report, we provide the first evidence, to our knowledge, of the geldanamycin (Ge)-inhibitable HSP90 on the surface of live monocyte-derived Mϕs (hMDMs). Using cytometry and specific Abs, we showed both HSP90 isoforms (α and β) on the surface of human monocytes and hMDMs. The cell-surface HSP90 pool was also labeled with cell-impermeable Ge derivatives. Confocal analysis of hMDMs revealed that HSP90-inhibitor complexes were rapidly clustered on the cell surface and recycled through the endosomal compartment. This finding suggests that the N-terminal (ATPase) domain of HSP90 is exposed and accessible from the extracellular space. To study the role of cell-surface HSP90 in pattern recognition, we used pathogen (PAMPs)- or apoptotic cell-associated molecular patterns (ACAMPs). We showed that blocking the cell-surface HSP90 pool leads to a dramatic decrease in TNF production by monocytes and hMDMs exposed to soluble (TLRs-specific ligands) and particulate [bacteria Staphylococcus aureus (SA) and Porphyromonas gingivalis (PG)] PAMPs. Surprisingly, in hMDMs the functional cell-surface HSP90 was not necessary for the engulfment of either apoptotic neutrophils or bacteria. The presented data suggest that the cell-surface HSP90 is a "signaling complex chaperone," with activity that is essential for cytokine response but not for target engulfment by Mϕ.

MMP generated matrikines

Matrikines originate from the fragmentation of extracellular matrix proteins and regulate cellular activities by interacting with specific receptors. Matrikines are implicated in inflammation, immune responses, organ development, wound repair, angiogenesis, atherosclerosis, tumor progression and metastasis due to their ability to alter cellular migration, chemotaxis, and mitogenesis. Matrix metalloproteinases (MMPs) degrade extracellular matrix components under normal circumstances and in disease processes. Of the 20 MMPs identified, MMP-1, MMP-2, MMP-8, MMP-9, and MMP-12 have been implicated in regulating the matrikines Val-Gly-Val-Ala-Pro-Gly (elastin peptide) and proline-glycine-proline (PGP). Elastin peptide fragments are generated by elastolytic enzymes and have implications in atherosclerosis, neovascularization, chronic obstructive pulmonary disease, skin disease, as well as tumor invasion and spread. PGP is produced through a multistep pathway that liberates the tripeptide fragment from extracellular collagen. PGP is best described for its role in neutrophil chemotaxis and is implicated in the pathogenesis of corneal ulcers and in chronic lung conditions. In chronic cigarette smoke related lung disease, the PGP pathway can become a self-propagating cycle of inflammation through cigarette-smoke mediated inhibition of leukotriene A4 hydrolase, the enzyme responsible for degrading PGP and halting acute inflammation. This review highlights the roles of MMPs in generating these important matrikines.

Heat-shock proteins in cardiovascular disease

Heat-shock proteins (HSPs) belong to a group of highly conserved families of proteins expressed by all cells and organisms and their expression may be constitutive or inducible. They are generally considered as protective molecules against different types of stress and have numerous intracellular functions. Secretion or release of HSPs has also been described, and potential roles for extracellular HSPs reported. HSP expression is modulated by different stimuli involved in all steps of atherogenesis including oxidative stress, proteolytic aggression, or inflammation. Also, antibodies to HSPs may be used to monitor the response to different types of stress able to induce changes in HSP levels. In the present review, we will focus on the potential implication of HSPs in atherogenesis and discuss the limitations to the use of HSPs and anti-HSPs as biomarkers of atherothrombosis. HSPs could also be considered as potential therapeutic targets to reinforce vascular defenses and delay or avoid clinical complications associated with atherothrombosis.