Motoneurons secrete angiogenin to induce RNA cleavage in astroglia

New evidence of vascular defects in neurodegenerative diseases revealed by single cell RNA sequencing

Neurodegenerative diseases (NDs) involve the progressive loss of neuronal structure or function in the brain and spinal cord. Despite their diverse etiologies, NDs manifest similar pathologies. Emerging research identifies vascular defects as a previously neglected hallmark of NDs. The development and popularization of single-cell RNA sequencing (scRNA-seq) technologies have significantly advanced our understanding of brain vascular cell types and their molecular characteristics, including gene expression changes at the single-cell level in NDs. These unprecedented insights deepen our understanding of the pathogenic mechanisms underlying NDs. However, the occurrence and role of vascular defects in disease progression remain largely unexplored. In this paper, we systematically summarize recent advances in the structure and organization of the central nervous system vasculature in mice, healthy individuals, and patients with NDs, focussing primarily on disease-specific alterations in vascular cell types or subtypes. Combining scRNA-seq with pathology evidence, we propose that vascular defects, characterized by disruptions in cell types and structural integrity, may serve as common early features of NDs. Finally, we discuss several pathways through which vascular defects in NDs lead to neuronal degeneration. A deeper understanding of the causes and contributions of vascular defects to NDs aids in elucidating the pathogenic mechanisms and developing meaningful therapeutic interventions.

Effects of Pathogenic Mutants of the Neuroprotective RNase 5-Angiogenin in Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that affects the motoneurons. More than 40 genes are related with ALS, and amyloidogenic proteins like SOD1 and/or TDP-43 mutants are directly involved in the onset of ALS through the formation of polymorphic fibrillogenic aggregates. However, efficacious therapeutic approaches are still lacking. Notably, heterozygous missense mutations affecting the gene coding for RNase 5, an enzyme also called angiogenin (ANG), were found to favor ALS onset. This is also true for the less-studied but angiogenic RNase 4. This review reports the substrate targets and illustrates the neuroprotective role of native ANG in the neo-vascularization of motoneurons. Then, it discusses the molecular determinants of many pathogenic ANG mutants, which almost always cause loss of function related to ALS, resulting in failures in angiogenesis and motoneuron protection. In addition, ANG mutations are sometimes combined with variants of other factors, thereby potentiating ALS effects. However, the activity of the native ANG enzyme should be finely balanced, and not excessive, to avoid possible harmful effects. Considering the interplay of these angiogenic RNases in many cellular processes, this review aims to stimulate further investigations to better elucidate the consequences of mutations in ANG and/or RNase 4 genes, in order to achieve early diagnosis and, possibly, successful therapies against ALS.

Structural mechanism of angiogenin activation by the ribosome

Angiogenin, an RNase-A-family protein, promotes angiogenesis and has been implicated in cancer, neurodegenerative diseases and epigenetic inheritance1-10. After activation during cellular stress, angiogenin cleaves tRNAs at the anticodon loop, resulting in translation repression11-15. However, the catalytic activity of isolated angiogenin is very low, and the mechanisms of the enzyme activation and tRNA specificity have remained a puzzle3,16-23. Here we identify these mechanisms using biochemical assays and cryogenic electron microscopy (cryo-EM). Our study reveals that the cytosolic ribosome is the activator of angiogenin. A cryo-EM structure features angiogenin bound in the A site of the 80S ribosome. The C-terminal tail of angiogenin is rearranged by interactions with the ribosome to activate the RNase catalytic centre, making the enzyme several orders of magnitude more efficient in tRNA cleavage. Additional 80S-angiogenin structures capture how tRNA substrate is directed by the ribosome into angiogenin's active site, demonstrating that the ribosome acts as the specificity factor. Our findings therefore suggest that angiogenin is activated by ribosomes with a vacant A site, the abundance of which increases during cellular stress24-27. These results may facilitate the development of therapeutics to treat cancer and neurodegenerative diseases.

RNA: The Unsuspected Conductor in the Orchestra of Macromolecular Crowding

This comprehensive Review delves into the chemical principles governing RNA-mediated crowding events, commonly referred to as granules or biological condensates. We explore the pivotal role played by RNA sequence, structure, and chemical modifications in these processes, uncovering their correlation with crowding phenomena under physiological conditions. Additionally, we investigate instances where crowding deviates from its intended function, leading to pathological consequences. By deepening our understanding of the delicate balance that governs molecular crowding driven by RNA and its implications for cellular homeostasis, we aim to shed light on this intriguing area of research. Our exploration extends to the methodologies employed to decipher the composition and structural intricacies of RNA granules, offering a comprehensive overview of the techniques used to characterize them, including relevant computational approaches. Through two detailed examples highlighting the significance of noncoding RNAs, NEAT1 and XIST, in the formation of phase-separated assemblies and their influence on the cellular landscape, we emphasize their crucial role in cellular organization and function. By elucidating the chemical underpinnings of RNA-mediated molecular crowding, investigating the role of modifications, structures, and composition of RNA granules, and exploring both physiological and aberrant phase separation phenomena, this Review provides a multifaceted understanding of the intriguing world of RNA-mediated biological condensates.

Oxidative Stress, Transfer RNA Metabolism, and Protein Synthesis

Significance: Oxidative stress refers to excessive intracellular levels of reactive oxygen species (ROS) due to an imbalance between ROS production and the antioxidant defense system. Under oxidative stress conditions, cells trigger various stress response pathways to protect themselves, among which repression of messenger RNA (mRNA) translation is one of the key hallmarks promoting cell survival. This regulation process minimizes cellular energy consumption, enabling cells to survive in adverse conditions and to promote recovery from stress-induced damage. Recent Advances: Recent studies suggest that transfer RNAs (tRNAs) play important roles in regulating translation as a part of stress response under adverse conditions. In particular, research relying on high-throughput techniques such as next-generation sequencing and mass spectrometry approaches has given us detailed information on mechanisms such as individual tRNA dynamics and crosstalk among post-transcriptional modifications. Critical Issues: Oxidative stress leads to dynamic tRNA changes, including their localization, cleavage, and alteration of expression profiles and modification patterns. Growing evidence suggests that these changes not only are tightly regulated by stress response mechanisms, but also can directly fine-tune the translation efficiency, which contributes to cell- or tissue-specific response to oxidative stress. Future Directions: In this review, we describe recent advances in the understanding of the dynamic changes of tRNAs caused by oxidative stress. We also highlight the emerging roles of tRNAs in translation regulation under the condition of oxidative stress. In addition, we discuss future perspectives in this research field. Antioxid. Redox Signal. 40, 715-735.

Neural stem cell homeostasis is affected in cortical organoids carrying a mutation in Angiogenin

Mutations in Angiogenin (ANG) and TARDBP encoding the 43 kDa transactive response DNA binding protein (TDP-43) are associated with amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). ANG is neuroprotective and plays a role in stem cell dynamics in the haematopoietic system. We obtained skin fibroblasts from members of an ALS-FTD family, one with mutation in ANG, one with mutation in both TARDBP and ANG, and one with neither mutation. We reprogrammed these fibroblasts to induced pluripotent stem cells (iPSCs) and generated cortical organoids as well as induced stage-wise differentiation of the iPSCs to neurons. Using these two approaches we investigated the effects of FTD-associated mutations in ANG and TARDBP on neural precursor cells, neural differentiation, and response to stress. We observed striking neurodevelopmental defects such as abnormal and persistent rosettes in the organoids accompanied by increased self-renewal of neural precursor cells. There was also a propensity for differentiation to later-born neurons. In addition, cortical neurons showed increased susceptibility to stress, which is exacerbated in neurons carrying mutations in both ANG and TARDBP. The cortical organoids and neurons generated from patient-derived iPSCs carrying ANG and TARDBP gene variants recapitulate dysfunctions characteristic of frontotemporal lobar degeneration observed in FTD patients. These dysfunctions were ameliorated upon treatment with wild type ANG. In addition to its well-established role during the stress response of mature neurons, ANG also appears to play a role in neural progenitor dynamics. This has implications for neurogenesis and may indicate that subtle developmental defects play a role in disease susceptibility or onset. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

A Neglected Gene: The Role of the ANG Gene in the Pathogenesis of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease with a poor prognosis. To date, more than 40 ALS-related genes have been identified. However, there is still a lack of targeted therapeutic drugs for the treatment of ALS, especially for patients with acute onset and severe disease. A series of studies reported missense heterozygous mutations with loss of function in the coding region of the ANG gene in ALS patients. ANG deficiency is related to the pathogenesis of ALS, but the underlying mechanism has not been determined. This article aimed to synthesize and consolidate the knowledge of the pathological mechanism of ALS induced by ANG mutation and provide a theoretical basis for ALS diagnosis and targeted therapy. This article further delves into the mechanisms underlying the current understanding of the structure and function of the ANG gene, the association between ANG and ALS, and its pathogenesis. Mutations in ANG may lead to the development of ALS through the loss of neuroprotective function, induction of oxidative stress, or inhibition of rRNA synthesis. ANG mutations and genetic and environmental factors may cause disease heterogeneity and more severe disease than in ALS patients with the wild-type gene. Exploring this mechanism is expected to provide a new approach for ALS treatment through increasing ANG expression or angiogenin activity. However, the related study is still in its infancy; therefore, this article also highlights the need for further exploration of the application of ANG gene mutations in clinical trials and animal experiments is needed to achieve improved early diagnosis and treatment of ALS.

tRNA-derived RNAs: Biogenesis and roles in translational control

Transfer RNA (tRNA)-derived RNAs (tDRs) are a class of small non-coding RNAs that play important roles in different aspects of gene expression. These ubiquitous and heterogenous RNAs, which vary across different species and cell types, are proposed to regulate various biological processes. In this review, we will discuss aspects of their biogenesis, and specifically, their contribution into translational control. We will summarize diverse roles of tDRs and the molecular mechanisms underlying their functions in the regulation of protein synthesis and their impact on related events such as stress-induced translational reprogramming. This article is categorized under: RNA Processing > Processing of Small RNAs Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs Regulatory RNAs/RNAi/Riboswitches > Biogenesis of Effector Small RNAs.

Prospects for gene replacement therapies in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating and incurable neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons. ALS causes death, usually within 2-5 years of diagnosis. Riluzole, the only drug currently approved in Europe for the treatment of this condition, offers only a modest benefit, increasing survival by 3 months on average. Recent advances in our understanding of causative or disease-modifying genetic variants and in the development of genetic therapy strategies present exciting new therapeutic opportunities for ALS. In addition, the approval of adeno-associated virus-mediated delivery of functional copies of the SMN1 gene to treat spinal muscular atrophy represents an important therapeutic milestone and demonstrates the potential of gene replacement therapies for motor neuron disorders. In this Review, we describe the current landscape of genetic therapies in ALS, highlighting achievements and critical challenges. In particular, we discuss opportunities for gene replacement therapy in subgroups of people with ALS, and we describe loss-of-function mutations that are known to contribute to the pathophysiology of ALS and could represent novel targets for gene replacement therapies.

Quantification of substoichiometric modification reveals global tsRNA hypomodification, preferences for angiogenin-mediated tRNA cleavage, and idiosyncratic epitranscriptomes of human neuronal cell-lines

Modification of tRNA is an integral part of the epitranscriptome with a particularly pronounced potential to generate diversity in RNA expression. Eukaryotic tRNA contains modifications in up to 20% of their nucleotides, but not all sites are always fully modified. Combinations and permutations of partially modified sites in tRNAs can generate a plethora of tRNA isoforms, termed modivariants. Here, we investigate the stoichiometry of incompletely modified sites in tRNAs from human cell lines for their information content. Using a panel of RNA modification mapping methods, we assess the stoichiometry of sites that contain the modifications 5-methylcytidine (m5C), 2'-O-ribose methylation (Nm), 3-methylcytidine (m3C), 7-methylguanosine (m7G), and Dihydrouridine (D). We discovered that up to 75% of sites can be incompletely modified and that the differential modification status of a cellular tRNA population holds information that allows to discriminate e.g. different cell lines. As a further aspect, we investigated potential causal connectivity between tRNA modification and its processing into tRNA fragments (tiRNAs and tRFs). Upon exposure of cultured living cells to cell-penetrating angiogenin, the modification patterns of the corresponding RNA populations was changed. Importantly, we also found that tsRNAs were significantly less modified than their parent tRNAs at numerous sites, suggesting that tsRNAs might derive chiefly from hypomodified tRNAs.

Protective Effects of Recombinant Human Angiogenin in Keratinocytes: New Insights on Oxidative Stress Response Mediated by RNases

Human angiogenin (ANG) is a 14-kDa ribonuclease involved in different pathophysiological processes including tumorigenesis, neuroprotection, inflammation, innate immunity, reproduction, the regeneration of damaged tissues and stress cell response, depending on its intracellular localization. Under physiological conditions, ANG moves to the cell nucleus where it enhances rRNA transcription; conversely, recent reports indicate that under stress conditions, ANG accumulates in the cytoplasmic compartment and modulates the production of tiRNAs, a novel class of small RNAs that contribute to the translational inhibition and recruitment of stress granules (SGs). To date, there is still limited and controversial experimental evidence relating to a hypothetical role of ANG in the epidermis, the outermost layer of human skin, which is continually exposed to external stressors. The present study collects compelling evidence that endogenous ANG is able to modify its subcellular localization on HaCaT cells, depending on different cellular stresses. Furthermore, the use of recombinant ANG allowed to determine as this special enzyme is effectively able to counter at various levels the alterations of cellular homeostasis in HaCaT cells, actually opening a new vision on the possible functions that this special enzyme can support also in the stress response of human skin.

Angiogenin promotes angiogenesis via the endonucleolytic decay of miR-141 in colorectal cancer

Mature microRNA (miRNA) decay is a key step in miRNA turnover and gene expression regulation. Angiogenin (ANG), the first human tumor-derived angiogenic protein and also a member of the RNase A superfamily, can promote tumor growth and metastasis by regulating rRNA biogenesis and tiRNA production. However, its effect on miRNA has not been explored. In this study, we find that ANG exclusively downregulates mature miR-141 in human umbilical endothelial cells (HUVECs) via its ribonuclease activity and preferably cleaves single-stranded miR-141 at the A⁵/C⁶, U⁷/G⁸, and U¹⁴/A¹⁵ sites via endonucleolytic digestion. By downregulating miR-141, ANG promotes HUVECs proliferation, migration, tube formation, and angiogenesis both in vitro and in vivo. Conversely, downregulated ANG inhibits ANG-mediated miR-141 decay, thus decreasing the angiogenesis process of HUVECs. We also find an inverse correlation between ANG and miR-141 expression in colorectal cancer (CRC) tissues. Our study indicates that ANG regulates CRC progression by disrupting miR-141 and its regulation on angiogenesis-related target genes, not only revealing a new mechanism of ANG action but also newly identifying miR-141 as a substrate of ANG. This study suggests that targeting ANG nuclease activity might be valuable in treating angiogenesis-related diseases through coordinately regulating the metabolism of rRNA, tiRNA, and miRNA.

Transfer RNA-Derived Fragments and isomiRs Are Novel Components of Chronic TBI-Induced Neuropathology

Neuroinflammation is a secondary injury mechanism that evolves in the brain for months after traumatic brain injury (TBI). We hypothesized that an altered small non-coding RNA (sncRNA) signature plays a key role in modulating post-TBI secondary injury and neuroinflammation. At 3threemonths post-TBI, messenger RNA sequencing (seq) and small RNAseq were performed on samples from the ipsilateral thalamus and perilesional cortex of selected rats with a chronic inflammatory endophenotype, and sham-operated controls. The small RNAseq identified dysregulation of 2 and 19 miRNAs in the thalamus and cortex, respectively. The two candidates from the thalamus and the top ten from the cortex were selected for validation. In the thalamus, miR-146a-5p and miR-155-5p levels were upregulated, and in the cortex, miR-375-3p and miR-211-5p levels were upregulated. Analysis of isomiRs of differentially expressed miRNAs identified 3′ nucleotide additions that were increased after TBI. Surprisingly, we found fragments originating from 16 and 13 tRNAs in the thalamus and cortex, respectively. We further analyzed two upregulated fragments, 3′tRF-IleAAT and 3′tRF-LysTTT. Increased expression of the full miR-146a profile, and 3′tRF-IleAAT and 3′tRF-LysTTT was associated with a worse behavioral outcome in animals with chronic neuroinflammation. Our results highlight the importance of understanding the regulatory roles of as-yet unknown sncRNAs for developing better strategies to treat TBI and neuroinflammation.

Emerging biological functions of ribonuclease 1 and angiogenin

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

SLM2 Is A Novel Cardiac Splicing Factor Involved in Heart Failure due to Dilated Cardiomyopathy

Alternative mRNA splicing is a fundamental process to increase the versatility of the genome. In humans, cardiac mRNA splicing is involved in the pathophysiology of heart failure. Mutations in the splicing factor RNA binding motif protein 20 (RBM20) cause severe forms of cardiomyopathy. To identify novel cardiomyopathy-associated splicing factors, RNA-seq and tissue-enrichment analyses were performed, which identified up-regulated expression of Sam68-Like mammalian protein 2 (SLM2) in the left ventricle of dilated cardiomyopathy (DCM) patients. In the human heart, SLM2 binds to important transcripts of sarcomere constituents, such as those encoding myosin light chain 2 (MYL2), troponin I3 (TNNI3), troponin T2 (TNNT2), tropomyosin 1/2 (TPM1/2), and titin (TTN). Mechanistically, SLM2 mediates intron retention, prevents exon exclusion, and thereby mediates alternative splicing of the mRNA regions encoding the variable proline-, glutamate-, valine-, and lysine-rich (PEVK) domain and another part of the I-band region of titin. In summary, SLM2 is a novel cardiac splicing regulator with essential functions for maintaining cardiomyocyte integrity by binding to and processing the mRNAs of essential cardiac constituents such as titin.

tRNA-derived fragments: A new class of non-coding RNA with key roles in nervous system function and dysfunction

tRNA-derived small RNAs (tsRNA) are a recently identified family of non-coding RNA that have been associated with a variety of cellular functions including the regulation of protein translation and gene expression. Recent sequencing and bioinformatic studies have identified the broad spectrum of tsRNA in the nervous system and demonstrated that this new class of non-coding RNA is produced from tRNA by specific cleavage events catalysed by ribonucleases such as angiogenin and dicer. Evidence is also accumulating that production of tsRNA is increased during disease processes where they regulate stress responses, proteostasis, and neuronal survival. Mutations to tRNA cleaving and modifying enzymes have been implicated in several neurodegenerative disorders, and tsRNA levels in the blood are advancing as biomarkers for neurological disease. In this review we summarize the physiological importance of tsRNA in the central nervous system and their relevance to neurological disease.

Strengths and Challenges of Secretory Ribonucleases as AntiTumor Agents

Approaches to develop effective drugs to kill cancer cells are mainly focused either on the improvement of the currently used chemotherapeutics or on the development of targeted therapies aimed at the selective destruction of cancer cells by steering specific molecules and/or enhancing the immune response. The former strategy is limited by its genotoxicity and severe side effects, while the second one is not always effective due to tumor cell heterogeneity and variability of targets in cancer cells. Between these two strategies, several approaches target different types of RNA in tumor cells. RNA degradation alters gene expression at different levels inducing cell death. However, unlike DNA targeting, it is a pleotropic but a non-genotoxic process. Among the ways to destroy RNA, we find the use of ribonucleases with antitumor properties. In the last few years, there has been a significant progress in the understanding of the mechanism by which these enzymes kill cancer cells and in the development of more effective variants. All the approaches seek to maintain the requirements of the ribonucleases to be specifically cytotoxic for tumor cells. These requirements start with the competence of the enzymes to interact with the cell membrane, a process that is critical for their internalization and selectivity for tumor cells and continue with the downstream effects mainly relying on changes in the RNA molecular profile, which are not only due to the ribonucleolytic activity of these enzymes. Although the great improvements achieved in the antitumor activity by designing new ribonuclease variants, some drawbacks still need to be addressed. In the present review, we will focus on the known mechanisms used by ribonucleases to kill cancer cells and on recent strategies to solve the shortcomings that they show as antitumor agents, mainly their pharmacokinetics.

ER Stress-Induced Secretion of Proteins and Their Extracellular Functions in the Heart

Endoplasmic reticulum (ER) stress is a result of conditions that imbalance protein homeostasis or proteostasis at the ER, for example ischemia, and is a common event in various human pathologies, including the diseased heart. Cardiac integrity and function depend on the active secretion of mature proteins from a variety of cell types in the heart, a process that requires an intact ER environment for efficient protein folding and trafficking to the secretory pathway. As a consequence of ER stress, most protein secretion by the ER secretory pathway is decreased. Strikingly, there is a select group of proteins that are secreted in greater quantities during ER stress. ER stress resulting from the dysregulation of ER Ca²⁺ levels, for instance, stimulates the secretion of Ca²⁺-binding ER chaperones, especially GRP78, GRP94, calreticulin, and mesencephalic astrocyte-derived neurotrophic factor (MANF), which play a multitude of roles outside the cell, strongly depending on the cell type and tissue. Here we review current insights in ER stress-induced secretion of proteins, particularly from the heart, and highlight the extracellular functions of these proteins, ranging from the augmentation of cardiac cell viability to the modulation of pro- and anti-apoptotic, oncogenic, and immune-stimulatory cell signaling, cell invasion, extracellular proteostasis, and more. Many of the roles of ER stress-induced protein secretion remain to be explored in the heart. This article is part of a special issue entitled “The Role of Proteostasis Derailment in Cardiac Diseases.”

5'ValCAC tRNA fragment generated as part of a protective angiogenin response provides prognostic value in amyotrophic lateral sclerosis

Loss-of-function mutations in the ribonuclease angiogenin are associated with amyotrophic lateral sclerosis. Angiogenin has been shown to cleave transfer RNAs during stress to produce ‘transfer-derived stress-induced RNAs’. Stress-induced tRNA cleavage is preserved from single-celled organisms to humans indicating it represents part of a highly conserved stress response. However, to date, the role of tRNA cleavage in amyotrophic lateral sclerosis remains to be fully elucidated. To this end, we performed small RNA sequencing on a human astrocytoma cell line to identify the complete repertoire of tRNA fragments generated by angiogenin. We found that only a specific subset of tRNAs is cleaved by angiogenin and identified 5′ValCAC transfer-derived stress-induced RNA to be secreted from neural cells. 5′ValCAC was quantified in spinal cord and serum from SOD1^G93A amyotrophic lateral sclerosis mouse models where we found it to be significantly elevated at symptom onset correlating with increased angiogenin expression, imbalanced protein translation initiation factors and slower disease progression. In amyotrophic lateral sclerosis patient serum samples, we found 5′ValCAC to be significantly higher in patients with slow disease progression, and interestingly, we find 5′ValCAC to hold prognostic value for amyotrophic lateral sclerosis patients. Here, we report that angiogenin cleaves a specific subset of tRNAs and provide evidence for 5′ValCAC as a prognostic biomarker in amyotrophic lateral sclerosis. We propose that increased serum 5′ValCAC levels indicate an enhanced angiogenin-mediated stress response within motor neurons that correlates with increased survival. These data suggest that the previously reported beneficial effects of angiogenin in SOD1^G93A mice may result from elevated levels of 5′ValCAC transfer RNA fragment.

Angiogenin and tRNA fragments in Parkinson's disease and neurodegeneration

In this review, we summarise the evidence for a role of the ribonuclease angiogenin in the pathophysiology of neurodegenerative disorders, with a specific focus on Parkinson’s disease (PD). Angiogenin is a stress-induced, secreted ribonuclease with both nuclear and cytosolic activities. Loss-of-function mutations in the angiogenin gene (ANG) have been initially discovered in familial cases of amyotrophic lateral sclerosis (ALS), however, variants in ANG have subsequently been identified in PD and Alzheimer’s disease. Delivery of angiogenin protein reduces neurodegeneration and delays disease progression in in vitro and in vivo models of ALS and in vitro models of PD. In the nucleus, angiogenin promotes ribosomal RNA transcription. Under stress conditions, angiogenin also translocates to the cytosol where it cleaves non-coding RNA into RNA fragments, in particular transfer RNAs (tRNAs). Stress-induced tRNA fragments have been proposed to have multiple cellular functions, including inhibition of ribosome biogenesis, inhibition of protein translation and inhibition of apoptosis. We will discuss recent evidence of tRNA fragment accumulation in PD, as well as their potential neuroprotective activities.

Loss of angiogenin function is related to earlier ALS onset and a paradoxical increase in ALS duration

0.5-1% of ALS (Amyotrophic Lateral Sclerosis) and Parkinson's disease (PD) are associated with mutations in the angiogenin (ANG). These mutations are thought to cause disease through a loss of ANG function, but this hypothesis has not been evaluated statistically. In addition, the potential for ANG to promote disease has not been considered. With the goal of better defining the etiology of ANG-ALS, we assembled all clinical onset and disease duration data and determined if these were correlated with biochemical properties of ANG variants. Loss of ANG stability and ribonuclease activity were found to correlate with early ALS onset, confirming an aspect of the prevailing model of ANG-ALS. Conversely, loss of ANG stability and ribonuclease activity correlated with longer survival following diagnosis, which is inconsistent with the prevailing model. These results indicate that functional ANG appears to decrease the risk of developing ALS but exacerbate ALS once in progress. These findings are rationalized in terms of studies demonstrating that distinct mechanisms contribute to ALS onset and progression and propose that ANG replacement or stabilization would benefit pre-symptomatic ANG-ALS patients. However, this study challenges the prevailing hypothesis that augmenting ANG will benefit symptomatic ANG-ALS patients. Instead, our results suggest that silencing of ANG activity may be beneficial for symptomatic ALS patients. This study will serve as a call-to-arms for neurologists to consistently publish ALS and PD patient's clinical data-if all ANG-ALS patients' data were available our findings could be tested with considerable statistical power.

Astrocytes in Motor Neuron Diseases

Motor neuron disorders are highly debilitating and mostly fatal conditions for which only limited therapeutic options are available. To overcome this limitation and develop more effective therapeutic strategies, it is critical to discover the pathogenic mechanisms that trigger and sustain motor neuron degeneration with the greatest accuracy and detail. In the case of Amyotrophic Lateral Sclerosis (ALS), several genes have been associated with familial forms of the disease, whilst the vast majority of cases develop sporadically and no defined cause can be held responsible. On the contrary, the huge majority of Spinal Muscular Atrophy (SMA) occurrences are caused by loss-of-function mutations in a single gene, SMN1. Although the typical hallmark of both diseases is the loss of motor neurons, there is increasing awareness that pathological lesions are also present in the neighbouring glia, whose dysfunction clearly contributes to generating a toxic environment in the central nervous system. Here, ALS and SMA are sequentially presented, each disease section having a brief introduction, followed by a focussed discussion on the role of the astrocytes in the disease pathogenesis. Such a dissertation is substantiated by the findings that built awareness on the glial involvement and how the glial-neuronal interplay is perturbed, along with the appraisal of this new cellular site for possible therapeutic intervention.

Angiogenin generates specific stress-induced tRNA halves and is not involved in tRF-3-mediated gene silencing

tRNA fragments (tRFs) and tRNA halves have been implicated in various cellular processes, including gene silencing, translation, stress granule assembly, cell differentiation, retrotransposon activity, symbiosis, apoptosis, and more. Overexpressed angiogenin (ANG) cleaves tRNA anticodons and produces tRNA halves similar to those produced in response to stress. However, it is not clear whether endogenous ANG is essential for producing the stress-induced tRNA halves. It is also not clear whether smaller tRFs are generated from the tRNA halves. Here, using global short RNA-Seq approach, we found that ANG overexpression selectively cleaves a subset of tRNAs, including tRNA^Glu, tRNA^Gly, tRNA^Lys, tRNA^Val, tRNA^His, tRNA^Asp, and tRNA^SeC to produce tRNA halves and tRF-5s that are 26-30 bases long. Surprisingly, ANG knockout revealed that the majority of stress-induced tRNA halves, except for the 5' half from tRNA^HisGTG and the 3' half from tRNA^AspGTC, are ANG independent, suggesting there are other RNases that produce tRNA halves. We also found that the 17-25 bases-long tRF-3s and tRF-5s that could enter into Argonaute complexes are not induced by ANG overexpression, suggesting that they are generated independently from tRNA halves. Consistent with this, ANG knockout did not decrease tRF-3 levels or gene-silencing activity. We conclude that ANG cleaves specific tRNAs and is not the only RNase that creates tRNA halves and that the shorter tRFs are not generated from the tRNA halves or from independent tRNA cleavage by ANG.

Angiogenin activates the astrocytic Nrf2/antioxidant-response element pathway and thereby protects murine neurons from oxidative stress

The angiogenin (ANG) gene is mutated frequently in individuals with amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by the progressive loss of motor neurons. Delivering human ANG to mice that display ALS-like symptoms extends their lifespan and improves motor function. ANG is a secretory vertebrate RNase that enters neuronal cells and cleaves a subset of tRNAs, leading to the inhibition of translation initiation and the assembly of stress granules. Here, using murine neuronal and astrocytic cell lines, we find that ANG triggers the activation of the Nrf2 (nuclear factor erythroid 2-related factor 2) pathway, which provides a critical cellular defense against oxidative stress. This activation, which occurred in astrocytes but not in neurons, promoted the survival of proximal neurons that had oxidative injury. These findings extend the role of ANG as a neuroprotective agent and underscore its potential utility in ALS management.

Functional roles of the human ribonuclease A superfamily in RNA metabolism and membrane receptor biology

The human ribonuclease A (hRNase A) superfamily is comprised of 13 members of secretory RNases, most of which are recognized as catabolic enzymes for their ribonucleolytic activity to degrade ribonucleic acids (RNAs) in the extracellular space, where they play a role in innate host defense and physiological homeostasis. Interestingly, human RNases 9-13, which belong to a non-canonical subgroup of the hRNase A superfamily, are ribonucleolytic activity-deficient proteins with unclear biological functions. Moreover, accumulating evidence indicates that secretory RNases, such as human RNase 5, can be internalized into cells facilitated by membrane receptors like the epidermal growth factor receptor to regulate intracellular RNA species, in particular non-coding RNAs, and signaling pathways by either a ribonucleolytic activity-dependent or -independent manner. In this review, we summarize the classical role of hRNase A superfamily in the metabolism of extracellular and intracellular RNAs and update its non-classical function as a cognate ligand of membrane receptors. We further discuss the biological significance and translational potential of using secretory RNases as predictive biomarkers or therapeutic agents in certain human diseases and the pathological settings for future investigations.

RNase A Promotes Proliferation of Neuronal Progenitor Cells via an ERK-Dependent Pathway

Members of the ribonuclease A (RNase A) superfamily regulate various physiological processes. RNase A, the best-studied member of the RNase A superfamily, is widely expressed in different tissues, including brains. We unexpectedly found that RNase A can trigger proliferation of neuronal progenitor cells (NPC) both in vitro and in vivo. RNase A treatment induced cell proliferation in dissociated neuronal cultures and increased cell mass in neurosphere cultures. BrdU (5-Bromo-2'-Deoxyuridine) labeling confirmed the effect of RNase A on cell proliferation. Those dividing cells were Nestin- and SOX2-positive, suggesting that RNase A triggers NPC proliferation. The proliferation inhibitor Ara-C completely suppressed the effect of RNase A on NPC counts, further supporting that RNase A increases NPC number mainly by promoting proliferation. Moreover, we found that RNase A treatment increased ERK phosphorylation and blockade of the ERK pathway inhibited the effect of RNase A on NPC proliferation. Intracerebroventricular injection of RNase A into mouse brain increased the population of 5-ethynyl-2'-deoxyuridine (EdU) or BrdU-labeled cells in the subventricular zone. Those RNase A-induced NPCs were able to migrate into other brain areas, including hippocampus, amygdala, cortex, striatum, and thalamus. In conclusion, our study shows that RNase A promotes proliferation of NPCs via an ERK-dependent pathway and further diversifies the physiological functions of the RNase A family.

Human angiogenin is a potent cytotoxin in the absence of ribonuclease inhibitor

Angiogenin (ANG) is a secretory ribonuclease that promotes the proliferation of endothelial cells, leading to angiogenesis. This function relies on its ribonucleolytic activity, which is low for simple RNA substrates. Upon entry into the cytosol, ANG is sequestered by the ribonuclease inhibitor protein (RNH1). We find that ANG is a potent cytotoxin for RNH1-knockout HeLa cells, belying its inefficiency as a nonspecific catalyst. The toxicity does, however, rely on the ribonucleolytic activity of ANG and a cytosolic localization, which lead to the accumulation of particular tRNA fragments (tRFs), such as tRF-5 Gly-GCC. These up-regulated tRFs are highly cytotoxic at physiological concentrations. Although ANG is well-known for its promotion of cell growth, our results reveal that ANG can also cause cell death.

Gold nanoparticles functionalized with angiogenin-mimicking peptides modulate cell membrane interactions

Angiogenin is a protein crucial in angiogenesis, and it is overexpressed in many cancers and downregulated in neurodegenerative diseases, respectively. The protein interaction with actin, through the loop encompassing the 60-68 residues, is an essential step in the cellular cytoskeleton reorganization. This, in turn, influences the cell proliferation and migration processes. In this work, hybrid nanoassemblies of gold nanoparticles with angiogenin fragments containing the 60-68 sequence were prepared and characterized in their interaction with both model membranes of supported lipid bilayers (SLBs) and cellular membranes of cancer (neuroblastoma) and normal (fibroblasts) cell lines. The comparison between physisorption and chemisorption mechanisms was performed by the parallel investigation of the 60-68 sequence and the peptide analogous containing an extra cysteine residue. Moreover, steric hindrance and charge effects were considered with a third analogous peptide sequence, conjugated with a fluorescent carboxyfluorescein (Fam) moiety. The hybrid nanobiointerface was characterized by means of ultraviolet-visible, atomic force microscopy and circular dichroism, to scrutinize plasmonic changes, nanoparticles coverage and conformational features, respectively. Lateral diffusion measurements on SLBs "perturbed" by the interaction with the gold nanoparticles-peptides point to a stronger membrane interaction in comparison with the uncoated nanoparticles. Cell viability and proliferation assays indicate a slight nanotoxicity in neuroblastoma cells and a proliferative activity in fibroblasts. The actin staining confirms different levels of interaction between the hybrid assemblies and the cell membranes.

Potential skin involvement in ALS: revisiting Charcot's observation - a review of skin abnormalities in ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons of the brain and spinal cord, leading to progressive paralysis and death. Interestingly, many skin changes have been reported in ALS patients, but never as yet fully explained. These observations could be due to the common embryonic origin of the skin and neural tissue known as the ectodermal germ layer. Following the first observation in ALS patients' skin by Dr Charcot in the 19th century, in the absence of bedsores unlike other bedridden patients, other morphological and molecular changes have been observed. Thus, the skin could be of interest in the study of ALS and other neurodegenerative diseases. This review summarizes skin changes reported in the literature over the years and discusses about a novel in vitro ALS tissue-engineered skin model, derived from patients, for the study of ALS.

The cellular uptake of angiogenin, an angiogenic and neurotrophic factor is through multiple pathways and largely dynamin independent

Angiogenin (ANG), a member of the RNase superfamily (also known as RNase 5) has neurotrophic, neuroprotective and angiogenic activities. Recently it has also been shown to be important in stem cell homeostasis. Mutations in ANG are associated with neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS) and Fronto-temporal dementia (FTD). ANG is a secreted protein which is taken up by cells and translocated to the nucleus. However, the import pathway/s through which ANG is taken up is/are still largely unclear. We have characterised the uptake of ANG in neuronal, astrocytic and microglial cell lines as well as primary neurons and astrocytes using pharmacological agents as well as dominant negative dynamin and Rab5 to perturb uptake and intracellular trafficking. We find that uptake of ANG is largely clathrin/dynamin independent and microtubule depolymerisation has a marginal effect. Perturbation of membrane ruffling and macropinocytosis significantly inhibited ANG uptake suggesting an uptake mechanism similar to RNase A. Our findings shed light on why mutations which do not overtly affect RNase activity but cause impaired localization are associated with neurodegenerative disease.

Pleiotropic activity of systemically delivered angiogenin in the SOD1G93A mouse model

Loss-of-function mutations in the angiogenin (ANG) gene have been identified in familial and sporadic ALS patients. Previous work from our group identified human ANG (huANG) to protect motoneurons in vitro, and provided proof-of-concept that daily intraperitoneal (i.p.) huANG injections post-symptom onset increased lifespan and delayed disease progression in SOD1^G93A mice. huANG's mechanism of action remains less well understood. Here, we implemented a preclinical in vivo design to validate our previous results, provide pharmacokinetic and protein distribution data after systemic administration, and explore potential pleiotropic activities of huANG in vivo. SOD1^G93A mice (n = 45) and non-transgenic controls (n = 31) were sex- age- and litter-matched according to the 2010 European ALS/MND group guidelines, and treated with huANG (1 μg, i.p., 3 times/week) or vehicle from 90 days on. huANG treatment increased survival and delayed motor dysfunction as assessed by rotarod in SOD1^G93A mice. Increased huANG serum levels were detectable 2 and 24 h after i.p. injection equally in transgenic and non-transgenic mice. Exogenous huANG localized to spinal cord astrocytes, supporting a glia-mediated, paracrine mechanism of action; uptake into endothelial cells was also observed. 1 μg huANG or vehicle were administered from 90 to 115 days of age for histological analysis. Vehicle-treated SOD1^G93A mice showed decreased motoneuron numbers and vascular length per ventral horn area, while huANG treatment resulted in improved vascular network maintenance and motoneuron survival. Our data suggest huANG represents a new class of pleiotropic ALS therapeutic that acts on the spinal cord vasculature and glia to delay motoneuron degeneration and disease progression.

hiPSC-derived neural stem cells from patients with schizophrenia induce an impaired angiogenesis

Schizophrenia is a neurodevelopmental disease characterized by cerebral connectivity impairment and loss of gray matter. It was described in adult schizophrenia patients (SZP) that concentration of VEGFA, a master angiogenic factor, is decreased. Recent evidence suggests cerebral hypoperfusion related to a dysfunctional Blood Brain Barrier (BBB) in SZP. Since neurogenesis and blood-vessel formation occur in a coincident and coordinated fashion, a defect in neurovascular development could result in increased vascular permeability and, therefore, in poor functionality of the SZP's neurons. Here, we characterized the conditioned media (CM) of human induced Pluripotent Stem Cells (hiPSC)-derived Neural Stem Cells of SZP (SZP NSC) versus healthy subjects (Ctrl NSC), and its impact on angiogenesis. Our results reveal that SZP NSC have an imbalance in the secretion and expression of several angiogenic factors, among them non-canonical neuro-angiogenic guidance factors. SZP NSC migrated less and their CM was less effective in inducing migration and angiogenesis both in vitro and in vivo. Since SZP originates during embryonic brain development, our findings suggest a defective crosstalk between NSC and endothelial cells (EC) during the formation of the neuro-angiogenic niche.

Spinal Cord Molecular and Cellular Changes Induced by Adenoviral Vector- and Cell-Mediated Triple Gene Therapy after Severe Contusion

The gene therapy has been successful in treatment of spinal cord injury (SCI) in several animal models, although it still remains unavailable for clinical practice. Surprisingly, regardless the fact that multiple reports showed motor recovery with gene therapy, little is known about molecular and cellular changes in the post-traumatic spinal cord following viral vector- or cell-mediated gene therapy. In this study we evaluated the therapeutic efficacy and changes in spinal cord after treatment with the genes encoding vascular endothelial growth factor (VEGF), glial cell-derived neurotrophic factor (GDNF), angiogenin (ANG), and neuronal cell adhesion molecule (NCAM) applied using both approaches. Therapeutic genes were used for viral vector- and cell-mediated gene therapy in two combinations: (1) VEGF+GDNF+NCAM and (2) VEGF+ANG+NCAM. For direct gene therapy adenoviral vectors based on serotype 5 (Ad5) were injected intrathecally and for cell-mediated gene delivery human umbilical cord blood mononuclear cells (UCB-MC) were simultaneously transduced with three Ad5 vectors and injected intrathecally 4 h after the SCI. The efficacy of both treatments was confirmed by improvement in behavioral (BBB) test. Molecular and cellular changes following post-traumatic recovery were evaluated with immunofluorescent staining using antibodies against the functional markers of motorneurons (Hsp27, synaptophysin, PSD95), astrocytes (GFAP, vimentin), oligodendrocytes (Olig2, NG2, Cx47) and microglial cells (Iba1). Our results suggest that both approaches with intrathecal delivery of therapeutic genes may support functional recovery of post-traumatic spinal cord via lowering the stress (down regulation of Hsp25) and enhancing the synaptic plasticity (up regulation of PSD95 and synaptophysin), supporting oligodendrocyte proliferation (up regulation of NG2) and myelination (up regulation of Olig2 and Cx47), modulating astrogliosis by reducing number of astrocytes (down regulation of GFAP and vimetin) and microglial cells (down regulation of Iba1).

RNA biology of angiogenin: Current state and perspectives

Angiogenin (ANG) is a secreted ribonuclease best known for its ability to promote formation of blood vessels. Extensive research over many years has elucidated its structure and biophysical properties, although our knowledge of molecular mechanisms underlying ANG-associated biologic processes remains limited. Intriguingly, many of processes require the ribonuclease activity of ANG, thus highlighting the importance of identifying and characterizing RNA targets and intermediates of ANG-mediated endonucleolytic cleavage. While ANG demonstrates ribonuclease activity toward many RNA substrates in vitro, specific target of ANG, namely mature tRNA, was only recently identified in vivo. ANG-mediated tRNA cleavage is an unorthodox manner of generating non-coding RNAs with diverse biologic activities. In addition, the ribonuclease activity of ANG has been reported to be crucial for rRNA transcription. Here we critically discuss various aspects of ANG biology related to its RNase activity and discuss areas in need of further investigation.

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.

Heparanase: Potential roles in multiple sclerosis

Heparanase is a heparan sulfate degrading enzyme that cleaves heparan sulfate (HS) chains present on HS proteoglycans (HSPGs), and has been well characterized for its roles in tumor metastasis and inflammation. However, heparanase is emerging as a contributing factor in the genesis and severity of a variety of neurodegenerative diseases and conditions. This is in part due to the wide variety of HSPGs on which the presence or absence of HS moieties dictates protein function. This includes growth factors, chemokines, cytokines, as well as components of the extracellular matrix (ECM) which in turn regulate leukocyte infiltration into the CNS. Roles for heparanase in stroke, Alzheimer's disease, and glioma growth have been described; roles for heparanase in other disease such as multiple sclerosis (MS) are less well established. However, given its known roles in inflammation and leukocyte infiltration, it is likely that heparanase also contributes to MS pathology. In this review, we will briefly summarize what is known about heparanase roles in the CNS, and speculate as to its potential role in regulating disease progression in MS and its animal model EAE (experimental autoimmune encephalitis), which may justify testing of heparanase inhibitors for MS treatment.

Dynamin regulates the fusion pore of endo- and exocytotic vesicles as revealed by membrane capacitance measurements

BACKGROUND

Dynamin is a multidomain GTPase exhibiting mechanochemical and catalytic properties involved in vesicle scission from the plasmalemma during endocytosis. New evidence indicates that dynamin is also involved in exocytotic release of catecholamines, suggesting the existence of a dynamin-regulated structure that couples endo- to exocytosis.

METHODS

Thus we here employed high-resolution cell-attached capacitance measurements and super-resolution structured illumination microscopy to directly examine single vesicle interactions with the plasmalemma in cultured rat astrocytes treated with distinct pharmacological modulators of dynamin activity. Fluorescent dextrans and the lipophilic plasmalemmal marker DiD were utilized to monitor uptake and distribution of vesicles in the peri-plasmalemmal space and in the cell cytosol.

RESULTS

Dynamin inhibition with Dynole™-34-2 and Dyngo™-4a prevented vesicle internalization into the cytosol and decreased fusion pore conductance of vesicles that remained attached to the plasmalemma via a narrow fusion pore that lapsed into a state of repetitive opening and closing - flickering. In contrast, the dynamin activator Ryngo™-1-23 promoted vesicle internalization and favored fusion pore closure by prolonging closed and shortening open fusion pore dwell times. Immunocytochemical staining revealed dextran uptake into dynamin-positive vesicles and increased dextran uptake into Syt4- and VAMP2-positive vesicles after dynamin inhibition, indicating prolonged retention of these vesicles at the plasmalemma.

CONCLUSIONS

Our results have provided direct evidence for a role of dynamin in regulation of fusion pore geometry and kinetics of endo- and exocytotic vesicles, indicating that both share a common dynamin-regulated structural intermediate, the fusion pore.

Yeast genetic interaction screen of human genes associated with amyotrophic lateral sclerosis: identification of MAP2K5 kinase as a potential drug target

To understand disease mechanisms, a large-scale analysis of human–yeast genetic interactions was performed. Of 1305 human disease genes assayed, 20 genes exhibited strong toxicity in yeast. Human–yeast genetic interactions were identified by en masse transformation of the human disease genes into a pool of 4653 homozygous diploid yeast deletion mutants with unique barcode sequences, followed by multiplexed barcode sequencing to identify yeast toxicity modifiers. Subsequent network analyses focusing on amyotrophic lateral sclerosis (ALS)-associated genes, such as optineurin (OPTN) and angiogenin (ANG), showed that the human orthologs of the yeast toxicity modifiers of these ALS genes are enriched for several biological processes, such as cell death, lipid metabolism, and molecular transport. When yeast genetic interaction partners held in common between human OPTN and ANG were validated in mammalian cells and zebrafish, MAP2K5 kinase emerged as a potential drug target for ALS therapy. The toxicity modifiers identified in this study may deepen our understanding of the pathogenic mechanisms of ALS and other devastating diseases.

A Boronic Acid Conjugate of Angiogenin that Shows ROS-Responsive Neuroprotective Activity

Angiogenin (ANG) is a human ribonuclease that is compromised in patients with amyotrophic lateral sclerosis (ALS). ANG also promotes neovascularization, and can induce hemorrhage and encourage tumor growth. The causal neurodegeneration of ALS is associated with reactive oxygen species, which are also known to elicit the oxidative cleavage of carbon-boron bonds. We have developed a synthetic boronic acid mask that restrains the ribonucleolytic activity of ANG. The masked ANG does not stimulate endothelial cell proliferation but protects astrocytes from oxidative stress. By differentiating between the two dichotomous biological activities of ANG, this strategy could provide a viable pharmacological approach for the treatment of ALS.

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.

Molecular basis for the autonomous promotion of cell proliferation by angiogenin

Canonical growth factors act indirectly via receptor-mediated signal transduction pathways. Here, we report on an autonomous pathway in which a growth factor is internalized, has its localization regulated by phosphorylation, and ultimately uses intrinsic catalytic activity to effect epigenetic change. Angiogenin (ANG), a secreted vertebrate ribonuclease, is known to promote cell proliferation, leading to neovascularization as well as neuroprotection in mammals. Upon entering cells, ANG encounters the cytosolic ribonuclease inhibitor protein, which binds with femtomolar affinity. We find that protein kinase C and cyclin-dependent kinase phosphorylate ANG, enabling ANG to evade its inhibitor and enter the nucleus. After migrating to the nucleolus, ANG cleaves promoter-associated RNA, which prevents the recruitment of the nucleolar remodeling complex to the ribosomal DNA promoter. The ensuing derepression of rDNA transcription promotes cell proliferation. The biochemical basis for this unprecedented mechanism of signal transduction suggests new modalities for the treatment of cancers and neurological disorders.

Three decades of research on angiogenin: a review and perspective

As a member of the vertebrate-specific secreted ribonucleases, angiogenin (ANG) was first isolated and identified solely by its ability to induce new blood vessel formation, and now, it has been recognized to play important roles in various physiological and pathological processes through regulating cell proliferation, survival, migration, invasion, and/or differentiation. ANG exhibits very weak ribonucleolytic activity that is critical for its biological functions, and exerts its functions through activating different signaling transduction pathways in different target cells. A series of recent studies have indicated that ANG contributes to cellular nucleic acid metabolism. Here, we comprehensively review the results of studies regarding the structure, mechanism, and function of ANG over the past three decades. Moreover, current problems and future research directions of ANG are discussed. The understanding of the function and mechanism of ANG in a wide context will help to better delineate its roles in diseases, especially in cancer and neurodegenerative diseases.

The established and emerging roles of astrocytes and microglia in amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two progressive, fatal neurodegenerative syndromes with considerable clinical, genetic and pathological overlap. Clinical symptoms of FTD can be seen in ALS patients and vice versa. Recent genetic discoveries conclusively link the two diseases, and several common molecular players have been identified (TDP-43, FUS, C9ORF72). The definitive etiologies of ALS and FTD are currently unknown and both disorders lack a cure. Glia, specifically astrocytes and microglia are heavily implicated in the onset and progression of neurodegeneration witnessed in ALS and FTD. In this review, we summarize the current understanding of the role of microglia and astrocytes involved in ALS and FTD, highlighting their recent implications in neuroinflammation, alterations in waste clearance involving phagocytosis and the newly described glymphatic system, and vascular abnormalities. Elucidating the precise mechanisms of how astrocytes and microglia are involved in ALS and FTD will be crucial in characterizing these two disorders and may represent more effective interventions for disease progression and treatment options in the future.