Three decades of research on angiogenin: a review and perspective

Fluorescence Sensing Using DNA Aptamers in Cancer Research and Clinical Diagnostics

Among the various advantages of aptamers over antibodies, remarkable is their ability to tolerate a large number of chemical modifications within their backbone or at the termini without losing significant activity. Indeed, aptamers can be easily equipped with a wide variety of reporter groups or coupled to different carriers, nanoparticles, or other biomolecules, thus producing valuable molecular recognition tools effective for diagnostic and therapeutic purposes. This review reports an updated overview on fluorescent DNA aptamers, designed to recognize significant cancer biomarkers both in soluble or membrane-bound form. In many examples, the aptamer secondary structure switches induced by target recognition are suitably translated in a detectable fluorescent signal using either fluorescently-labelled or label-free aptamers. The fluorescence emission changes, producing an enhancement (“signal-on”) or a quenching (“signal-off”) effect, directly reflect the extent of the binding, thereby allowing for quantitative determination of the target in bioanalytical assays. Furthermore, several aptamers conjugated to fluorescent probes proved to be effective for applications in tumour diagnosis and intraoperative surgery, producing tumour-type specific, non-invasive in vivo imaging tools for cancer pre- and post-treatment assessment.

Calcitriol promotes proangiogenic molecules in keratinocytes in a diabetic foot ulcer model

Foot ulceration is one of the most common and complex sequelae of diabetes mellitus, generally posing a therapeutic challenge due to poor healing responses and high rates of complications, including peripheral vascular disease, ischemia and infections. Calcitriol, the most active vitamin D metabolite, induces antimicrobial peptides production in keratinocytes from diabetic foot ulcers (DFU); however, little is known about its effects on angiogenic factors in this pathology. Herein we aimed at studying whether calcitriol induces angiogenic molecules in keratinocytes under normoxic and hypoxic conditions, and if these molecules are able to improve cell migration in vitro. Evaluation of DFU samples by immunohistochemistry showed increased VEGF and decreased angiogenin and HIF-1α expression compared to controls, suggesting an altered pattern of angiogenic factors in DFU. Interestingly, incubation of keratinocytes with calcitriol significantly upregulated VEGFA, HIF-1α and angiogenin gene expression, while the resulting cell culture media stimulated both endothelial cells and keratinocytes migration in an in vitro wound closure assay under a normoxic environment (p<0.05). Moreover, the culture media of calcitriol-treated keratinocytes stimulated cell migration in a similar extent as exogenous VEGF or EGF in endothelial and keratinocytes cells. These results suggest that the altered profile of angiogenic molecules in DFU might be improved by local or systemic treatment with calcitriol under normoxic conditions, which could probably be achieved with hyperbaric oxygen therapy. Given that calcitriol not only augments proangiogenic factors but also induces antimicrobial peptides expression, this hormone should be further investigated in clinical trials of DFU.

Proteomic Analysis of Human Angiogenin Interactions Reveals Cytoplasmic PCNA as a Putative Binding Partner

Human Angiogenin (hAng) is a member of the ribonuclease A superfamily and a potent inducer of neovascularization. Protein interactions of hAng in the nucleus and cytoplasm of the human umbilical vein cell line EA.hy926 have been investigated by mass spectroscopy. Data are available via ProteomeXchange with identifiers PXD006583 and PXD006584. The first gel-free analysis of hAng immunoprecipitates revealed many statistically significant potential hAng-interacting proteins involved in crucial biological pathways. Surprisingly, proliferating cell nuclear antigen (PCNA), was found to be immunoprecipitated with hAng only in the cytoplasm. The hAng-PCNA interaction and colocalization in the specific cellular compartment was validated with immunoprecipitation, immunoblotting, and immunocytochemistry. The results revealed that PCNA is predominantly localized in the cytoplasm, while hAng is distributed both in the nucleus and in the cytoplasm. hAng and PCNA colocalize in the cytoplasm, suggesting that they may interact in this compartment.

L-mimosine and hypoxia can increase angiogenin production in dental pulp-derived cells

Background

Angiogenin is a key molecule in the healing process which has been successfully applied in the field of regenerative medicine. The role of angiogenin in dental pulp regeneration is unclear. Here we aimed to reveal the impact of the hypoxia mimetic agent L-mimosine (L-MIM) and hypoxia on angiogenin in the dental pulp.

Methods

Human dental pulp-derived cells (DPC) were cultured in monolayer and spheroid cultures and treated with L-MIM or hypoxia. In addition, tooth slice organ cultures were applied to mimic the pulp-dentin complex. We measured angiogenin mRNA and protein levels using qPCR and ELISA, respectively. Inhibitor studies with echinomycin were performed to reveal the role of hypoxia-inducible factor (HIF)-1 signaling.

Results

Both, L-MIM and hypoxia increased the production of angiogenin at the protein level in monolayer cultures of DPC, while the increase at the mRNA level did not reach the level of significance. The increase of angiogenin in response to treatment with L-MIM or hypoxia was reduced by echinomycin. In spheroid cultures, L-MIM increased angiogenin at protein levels while the effect of hypoxia was not significant. Angiogenin was also expressed and released in tooth slice organ cultures under normoxic and hypoxic conditions and in the presence of L-MIM.

Conclusions

L-MIM and hypoxia modulate production of angiogenin via HIF-1 differentially and the response depends on the culture model. Given the role of angiogenin in regeneration the here presented results are of high relevance for pre-conditioning approaches for cell therapy and tissue engineering in the field of regenerative endodontics.

Extracellular Actin in Health and Disease

This review considers the functions of extracellular actin - cell surface bound, associated with extracellular matrix, or freely circulating. The role of this protein in different pathological processes is analyzed: its toxic effects and involvement in autoimmune diseases as an autoantigen. The extracellular actin clearance system and its role in protection against the negative effects of actin are characterized. Levels of free-circulating actin, anti-actin immunoglobulins, and components of the actin clearance system as prognostic biomarkers for different diseases are reviewed. Experimental approaches to protection against excessive amounts of free-circulating F-actin are discussed.

Structural insights into human angiogenin variants implicated in Parkinson's disease and Amyotrophic Lateral Sclerosis

Mutations in Angiogenin (ANG), a member of the Ribonuclease A superfamily (also known as RNase 5) are known to be associated with Amyotrophic Lateral Sclerosis (ALS, motor neurone disease) (sporadic and familial) and Parkinson’s Disease (PD). In our previous studies we have shown that ANG is expressed in neurons during neuro-ectodermal differentiation, and that it has both neurotrophic and neuroprotective functions. In addition, in an extensive study on selective ANG-ALS variants we correlated the structural changes to the effects on neuronal survival and the ability to induce stress granules in neuronal cell lines. Furthermore, we have established that ANG-ALS variants which affect the structure of the catalytic site and either decrease or increase the RNase activity affect neuronal survival. Neuronal cell lines expressing the ANG-ALS variants also lack the ability to form stress granules. Here, we report a detailed experimental structural study on eleven new ANG-PD/ALS variants which will have implications in understanding the molecular basis underlying their role in PD and ALS.

Short communication: Early-lactation, but not mid-lactation, bovine lactoferrin preparation increases epithelial barrier integrity of Caco-2 cell layers

Bovine lactoferrin is an important milk protein with many health-promoting properties, including improving intestinal barrier integrity. Dysfunction of this barrier, commonly referred to as "leaky gut," has been linked to inflammatory and autoimmune diseases. With some processing techniques, lactoferrin isolated from milk collected at the start of the milking season (early lactation) may have lower purity than that isolated from milk collected during the rest of the milking season (mid-lactation) and could result in differences in bioactivity based on the stage of lactation. We compared reversed-phase HPLC chromatographs of early-lactation and mid-lactation preparations and found that both had large chromatograph peaks at the time predicted for lactoferrin. The notable difference between the 2 chromatographs was a much larger peak in the early-lactation lactoferrin sample that was determined to be angiogenin. Angiogenin was first identified due to its ability to induce new blood vessel formation, but is now known to be involved in numerous physiological processes. Then, we compared the effects of early-lactation and mid-lactation lactoferrin preparations in 2 bioassays: trans-epithelial electrical resistance (TEER), a measure of intestinal barrier integrity, and peripheral blood mononuclear cell cytokine secretion, a measure of immune-stimulatory properties. We found that early-lactation lactoferrin increased TEER across Caco-2 cell layers compared with control from 10 to 48 h, mid-lactation lactoferrin did not alter TEER. We also found that early-lactation lactoferrin reduced the amount of IL-8 produced by peripheral blood mononuclear cells (compared with those treated with control medium) to a greater extent than mid-lactation lactoferrin. A pro-inflammatory chemokine, IL-8 is also known to decrease barrier function. These results suggest that the decrease in IL-8 production in the presence of early-lactation lactoferrin may be the mechanism by which it increases TEER. The anti-inflammatory effect of early-lactation lactoferrin may be related to the presence of angiogenin, which is known to suppress inflammatory responses. This work indicates that products rich in angiogenin may have intestinal health benefits, and further work to investigate this is warranted.

The Ribonuclease A Superfamily in Humans: Canonical RNases as the Buttress of Innate Immunity

In humans, the ribonuclease A (RNase A) superfamily contains eight different members that have RNase activities, and all of these members are encoded on chromosome 14. The proteins are secreted by a large variety of different tissues and cells; however, a comprehensive understanding of these proteins’ physiological roles is lacking. Different biological effects can be attributed to each protein, including antiviral, antibacterial and antifungal activities as well as cytotoxic effects against host cells and parasites. Different immunomodulatory effects have also been demonstrated. This review summarizes the available data on the human RNase A superfamily and illustrates the significant role of the eight canonical RNases in inflammation and the host defence system against infections.

Coordination Environment of Cu(II) Ions Bound to N-Terminal Peptide Fragments of Angiogenin Protein

Angiogenin (Ang) is a potent angiogenic factor, strongly overexpressed in patients affected by different types of cancers. The specific Ang cellular receptors have not been identified, but it is known that Ang-actin interaction induces changes both in the cell cytoskeleton and in the extracellular matrix. Most in vitro studies use the recombinant form (r-Ang) instead of the form that is normally present in vivo ("wild-type", wt-Ang). The first residue of r-Ang is a methionine, with a free amino group, whereas wt-Ang has a glutamic acid, whose amino group spontaneously cyclizes in the pyro-glutamate form. The Ang biological activity is influenced by copper ions. To elucidate the role of such a free amino group on the protein-copper binding, we scrutinized the copper(II) complexes with the peptide fragments Ang(1-17) and AcAng(1-17), which encompass the sequence 1-17 of angiogenin (QDNSRYTHFLTQHYDAK-NH₂), with free amino and acetylated N-terminus, respectively. Potentiometric, ultraviolet-visible (UV-vis), nuclear magnetic resonance (NMR) and circular dichroism (CD) studies demonstrate that the two peptides show a different metal coordination environment. Confocal microscopy imaging of neuroblastoma cells with the actin staining supports the spectroscopic results, with the finding of different responses in the cytoskeleton organization upon the interaction, in the presence or not of copper ions, with the free amino and the acetylated N-terminus peptides.