Vladimir Riabov

Stabilin-1 mediates phosphatidylserine-dependent clearance of cell corpses in alternatively activated macrophages

Stabilin-1 is specifically expressed in alternatively activated macrophages. These macrophages participate in anti-inflammatory and healing processes, and display a high phagocytic capacity. In this study, we provide evidence that stabilin-1 is a membrane receptor that performs a crucial function in the clearance of cell corpses. Stabilin-1 is expressed on the cell surface of alternatively activated macrophages and is recruited to the sites of recognition and engulfment of apoptotic bodies, as well as to early phagosomes. Blocking stabilin-1 in macrophages results in defective engulfment of aged red blood cells. Ectopic expression of stabilin-1 induces the binding and engulfment of aged cells in mouse fibroblast L cells. The binding and phagocytosis are dependent on phosphatidylserine (PS), which is well known as an engulfing ligand. Furthermore, using PS-coated beads, we demonstrate that PS directly interacts with stabilin-1 and is sufficient for stabilin-1-mediated phagocytosis. EGF-like domain repeat in stabilin-1 is responsible for PS recognition and binding. Thus, our results demonstrate that stabilin-1, found on alternatively activated macrophages, is a phagocytic receptor mediating the clearance of apoptotic cells in a PS-dependent manner. Therefore, this protein might play an important role in the maintenance of tissue homeostasis and prevention of autoimmunity.

Macrophage responses to implants: prospects for personalized medicine

Implants, transplants, and implantable biomedical devices are mainstream solutions for a wide variety of human pathologies. One of the persistent problems around nondegradable metallic and polymeric implants is failure of macrophages to resolve the inflammation and their tendency to stay in a state, named “frustrated phagocytosis.” During the initial phase, proinflammatory macrophages induce acute reactions to trauma and foreign materials, whereas tolerogenic anti‐inflammatory macrophages control resolution of inflammation and induce the subsequent healing stage. However, implanted materials can induce a mixed pro/anti‐inflammatory phenotype, supporting chronic inflammatory reactions accompanied by microbial contamination and resulting in implant failure. Several materials based on natural polymers for improved interaction with host tissue or surfaces that release anti‐inflammatory drugs/bioactive agents have been developed for implant coating to reduce implant rejection. However, no definitive, long‐term solution to avoid adverse immune responses to the implanted materials is available to date. The prevention of implant‐associated infections or chronic inflammation by manipulating the macrophage phenotype is a promising strategy to improve implant acceptance. The immunomodulatory properties of currently available implant coatings need to be improved to develop personalized therapeutic solutions. Human primary macrophages exposed to the implantable materials ex vivo can be used to predict the individuals reactions and allow selection of an optimal coating composition. Our review describes current understanding of the mechanisms of macrophage interactions with implantable materials and outlines the prospects for use of human primary macrophages for diagnostic and therapeutic approaches to personalized implant therapy.

A Novel GGA-Binding Site Is Required for Intracellular Sorting Mediated by Stabilin-1

ABSTRACT Stabilin-1 is a unique scavenger receptor that combines endocytic and intracellular sorting functions in macrophages. Stabilin-1 mediates the endocytosis of acetylated low-density lipoprotein (acLDL), SPARC, and growth hormone family member placental lactogen (PL). At the same time, stabilin-1 is involved in trans-Golgi network-to-endosome routing of the endogenous chitinase-like protein SI-CLP (stabilin-interacting chitinase-like protein). A DDSLL motif in the cytoplasmic tail of stabilin-1 interacts with GGA adaptors; however, the deletion of DDSLL reduces but does not abrogate this interaction. Here, we identified a novel GGA-binding site, EDDADDD, in the cytoplasmic tail of stabilin-1. The deletion of EDDADDD impaired and the deletion of both the DDSLL and EDDADDD sites abrogated the interaction of stabilin-1 with GGAs. The surface exposure of stabilin-1 and stabilin-1-mediated endocytosis of acLDL, SPARC, and PL were not affected by the deletion either of DDSLL or EDDADDD or both. At the same time, both GGA-binding sites were necessary for the intracellular sorting of SI-CLP performed by stabilin-1. Our data indicate that the novel GGA-binding site EDDADDD is essential for stabilin-1-mediated intracellular sorting but is not required for endocytosis.

Harnessing the Multifunctionality in Nature: A Bioactive Agent Release System with Self-Antimicrobial and Immunomodulatory Properties

Major problems with biomedical devices in particular implants located in nonsterile environments concern: (i) excessive immune response to the implant, (ii) development of bacterial biofilms, and (iii) yeast and fungi infections. An original multifunctional coating that addresses all these issues concomitantly is developed. A new exponentially growing polyelectrolyte multilayer film based on polyarginine (PAR) and hyaluronic acid (HA) is designed. The films have a strong inhibitory effect on the production of inflammatory cytokines released by human primary macrophage subpopulations. This could reduce potential chronic inflammatory reaction following implantation. Next, it is shown that PAR, due to its positive charges, has an antimicrobial activity in film format against Staphylococcus aureus for 24 h. In order to have a long-term antimicrobial activity, a precursor nanoscale silver coating is deposited on the surface before adding the PAR/HA films. Moreover, the PAR/HA films can be easily further functionalized by embedding antimicrobial peptides, like catestatin (CAT), a natural host defense peptide. This PAR/HA+CAT film proves to be effective as an antimicrobial coating against yeast and fungi and its cytocompatibility is also assessed. Finally, this all-in-one system constitutes an original strategy to limit inflammation and prevents bacteria, yeast, and fungi infections.

CD68+, but not stabilin-1+ tumor associated macrophages in gaps of ductal tumor structures negatively correlate with the lymphatic metastasis in human breast cancer

Tumor associated macrophages (TAM) support tumor growth and metastasis in several animal models of breast cancer, and TAM amount is predictive for efficient tumor growth and metastatic spread via blood circulation. However, limited information is available about intratumoral TAM heterogeneity and functional role of TAM subpopulations in tumor progression. The aim of our study was to examine correlation of TAM presence in various morphological segments of human breast cancer with clinical parameters. Thirty six female patients with nonspecific invasive breast cancer T1-4N0-3M0 were included in the study. Morphological examination was performed using Carl Zeiss Axio Lab.A1 and MiraxMidiZeiss. Immunohistochemical and immunofluorescence/confocal microcopy analysis was used to detect CD68 and stabilin-1 in 5 different tumor segments: (1) areas with soft fibrous stroma; (2) areas with coarse fibrous stroma; (3) areas of maximum stromal-and-parenchymal relationship; (4) parenchymal elements; (5) gaps of ductal tumor structures. The highest expression of CD68 was in areas with soft fibrous stroma or areas of maximum stromal-and-parenchymal relationship (79%). The lowest expression of CD68 was in areas with coarse fiber stroma (23%). Inverse correlation of tumor size and expression of CD68 in gaps of tubular tumor structures was found (R=-0.67; p=0.02). In case of the lymph node metastases the average score of CD68 expression in ductal gaps tumor structures was lower (1.4±0.5) compared to negative lymph nodes case (3.1±1.0; F=10.9; p=0.007). Confocal microscopy identified 3 phenotypes of TAM: CD68+/stabilin-1-; CD68+/stabilin-1+ (over 50%); and CD68-/stabilin-1+. However, expression of stabilin-1 did not correlate with lymph node metastasis. We concluded, that increased amount of CD68+TAM in gaps of ductal tumor structures is protective against metastatic spread in regional lymph nodes.

Novel monocyte biomarkers of atherogenic conditions.

Hidden low grade inflammation underlines various cardio-metabolic diseases. This type of inflammation is triggered by abnormal reaction to unwanted self products or deregulation of cellular response to cytokines. In the case of atherosclerosis hidden inflammation is induced by modified lipoproteins and develops under control of different cytokines including IL-4 and TGFβ. The key innate immune cells reacting on these factors are monocytes and macrophages. It is well established that monocytes represent a heterogeneous cell population that easily reacts to pathologic changes in the organism. The best studied marker which expression on monocytes is changed in inflammatory conditions is CD16. Although this marker was shown to be associated with various pathologic conditions its specificity is highly questionable. There is an urgent need of identification of new monocyte-expressed biomarkers that may help not only to detect hidden inflammation but also to determine its type. Our analysis of type 2 activation of human monocytes resulted in identification of 3 novel biomarkers for hidden type 2 inflammation. These include stabilin-1, FOXQ1 and IL17RB. These markers are expressed by monocytes/macrophages under stimulation with IL-4 or its combination with TGFβ - 2 cytokines playing important role in atherogenesis. Stabilin-1 was demonstrated on the monocytes in patients with hyperholisterolemia and in macrophages within atherosclerotic lesions. Association of FoxQ1 and IL17RB with atherosclerosis can be deduced from published data but requires experimental confirmation. Functions of all three proteins suggest that they are not only diagnostic markers, but also involved in atherogenesis and can be used as targets for novel therapeutic approaches.

Tumor-associated macrophages in human breast cancer parenchyma negatively correlate with lymphatic metastasis after neoadjuvant chemotherapy

Breast cancer is the leading cause of cancer death in women worldwide with high morbidity and mortality. Tumor-associated macrophages (TAM) are major innate immune cells in the tumor microenvironment controlling primary tumor growth and metastasis. Neoadjuvant chemotherapy (NACT) is a conventional pre-operative treatment for breast cancer. In the present study we examined the distribution of TAM in five distinct intratumoral morphological compartments of human breast cancer and their correlation with clinical parameters after NACT. Our data indicated that CD68+ but not stabilin-1+ TAM in areas with parenchymal elements negatively correlate with lymphatic metastasis after NACT. However, in cases where lymphatic metastases were detected (28 out of 50 analyzed samples) both amount of CD68+ and stabilin-1+ macrophages in the areas with coarse fibrous stroma directly correlated with the number of positive lymph nodes. In patients with complete response to the preoperative NACT the average score of CD68 expression in the areas with coarse fibrous stroma was lower compared with cases of a partial response and stable disease. We concluded that function of TAM after NACT depends on their intratumoral localization and local tumor microenvironment which plays an important role in polarization of macrophages towards tumor-suppressive or tumor-supportive types.

Deconvoluting hepatic processing of carbon nanotubes.

Single-wall carbon nanotubes present unique opportunities for drug delivery, but have not advanced into the clinic. Differential nanotube accretion and clearance from critical organs have been observed, but the mechanism not fully elucidated. The liver has a complex cellular composition that regulates a range of metabolic functions and coincidently accumulates most particulate drugs. Here we provide the unexpected details of hepatic processing of covalently functionalized nanotubes including receptor-mediated endocytosis, cellular trafficking and biliary elimination. Ammonium-functionalized fibrillar nanocarbon is found to preferentially localize in the fenestrated sinusoidal endothelium of the liver but not resident macrophages. Stabilin receptors mediate the endocytic clearance of nanotubes. Biocompatibility is evidenced by the absence of cell death and no immune cell infiltration. Towards clinical application of this platform, nanotubes were evaluated for the first time in non-human primates. The pharmacologic profile in cynomolgus monkeys is equivalent to what was reported in mice and suggests that nanotubes should behave similarly in humans.

Role of the immune component of tumor microenvironment in the efficiency of cancer treatment: perspectives for the personalized therapy

Despite significant progress in cancer diagnostics and development of novel therapeutic regimens, successful treatment of advanced forms of cancer is still a challenge and may require personalized therapeutic approaches. In this review, we analyzed major mechanisms responsible for tumor cells chemoresistance and emphasized that intratumor heterogeneity is a critical factor that limits efficiency of cancer treatment. Intratumor heterogeneity is caused by genomic instability in cancer cells, resulting in the selection of resistant clones. Moreover, cancer cells in solid tumors are surrounded by cellular and molecular microenvironment that actively influences tumor cell behavior. Local tumor microenvironment (TME) consisting of immune cells with diverse phenotypes and functions strongly contributes to intratumor heterogeneity and modulates responses to treatment. Thus, targeting specific components of TME is a novel treatment strategy that can improve the outcome of conventional anti-cancer therapy. Here, we discuss modern immunotherapeutic approaches based on targeting tumorinfiltrating immune cells including neutrophils, dendritic cells, NK cells, T cells, B cells and macrophages. Among those, tumor-associated macrophages (TAM) that display a pronounced heterogeneity and phenotypic plasticity appear to be a major component in the TME of solid tumors, and emerge as perspective targets for cancer immunotherapy. TAM intratumor heterogeneity and the possible existence of patient-specific phenotype signature generate the basis for the development of individualized TAM-based therapeutic approaches.

Stabilin-1 is expressed in human breast cancer and supports tumor growth in mammary adenocarcinoma mouse model

Stabilin-1 is a multifunctional scavenger receptor expressed on alternatively-activated macrophages. Stabilin-1 mediates phagocytosis of “unwanted-self” components, intracellular sorting, and endocytic clearance of extracellular ligands including SPARC that modulates breast cancer growth. The expression of stabilin-1 was found on tumor-associated macrophages (TAM) in mouse and human cancers including melanoma, lymphoma, glioblastoma, and pancreatic insulinoma. Despite its tumor-promoting role in mouse models of melanoma and lymphoma the expression and functional role of stabilin-1 in breast cancer was unknown. Here, we demonstrate that stabilin-1 is expressed on TAM in human breast cancer, and its expression is most pronounced on stage I disease. Using stabilin-1 knockout (ko) mice we show that stabilin-1 facilitates growth of mouse TS/A mammary adenocarcinoma. Endocytosis assay on stabilin-1 ko TAM demonstrated impaired clearance of stabilin-1 ligands including SPARC that was capable of inducing cell death in TS/A cells. Affymetrix microarray analysis on purified TAM and reporter assays in stabilin-1 expressing cell lines demonstrated no influence of stabilin-1 expression on intracellular signalling. Our results suggest stabilin-1 mediated silent clearance of extracellular tumor growth-inhibiting factors (e.g. SPARC) as a mechanism of stabilin-1 induced tumor growth. Silent clearance function of stabilin-1 makes it an attractive candidate for delivery of immunomodulatory anti-cancer therapeutic drugs to TAM.