Neuron-specific ablation of eIF5A or deoxyhypusine synthase leads to impairments in growth, viability, neurodevelopment, and cognitive functions in mice

Identifying Immune Response Protein Biomarkers in Parkinson's-Related Cognitive Impairment and Depression

A distinct immune microenvironment may develop in patients with Parkinson's disease (PD), influenced by the severity of cognitive impairment and the presence of depression. We aimed to identify blood-based immune response markers in patients with PD using a proximity extension assay (PEA). Peripheral plasma samples from 58 patients with PD and 30 healthy controls (HCs) were analyzed for 92 immune response-associated proteins using Olink's PEA technology. A panel of four proteins (SIT1, CLEC4C, EIF5A, and NFATC3) was identified, effectively differentiating patients with PD from HCs, with a combined area under the receiver operating characteristic (ROC) curve of 0.863. Among these, ITGA11 and EIF5A were particularly associated with the degree of cognitive impairment. After applying Bonferroni correction, five proteins-PPP1R9B, MILR1, BTN3A2, IRAK1, and TANK-demonstrated potentially significant differences between depressed and non-depressed patients with PD-cognitively normal (PD-CN). In the correlation analyses, PPP1R9B exhibited a positive correlation with the Hamilton Depression Rating Scale (HAMD) score (r = 0.509, P = 0.019). Furthermore, after adjusting for potential confounding factors in binary logistic regression analysis, PPP1R9B remained significantly associated with depression (P = 0.042). We identified potential blood-based immune response markers associated with the severity of cognitive impairment and depression in patients with PD. These findings provide preliminary insights into the immune-related pathology underlying non-motor symptoms of PD, potentially guiding future studies aimed at targeted therapeutic strategies. Further validation in larger, independent cohorts is warranted to confirm these associations and their clinical utility.

Hypusinated and unhypusinated isoforms of the translation factor eIF5A exert distinct effects in models of pancreas development and function

Hypusination of eukaryotic translation initiation factor 5A (eIF5A) is essential for its role in translation elongation and termination. Although the function of hypusinated eIF5A (eIF5AHyp) in cellular proliferation is well characterized, the role of its unhypusinated form (eIF5ALys) remains unclear. We hypothesized that eIF5ALys exerts independent and negative effects on cellular replication and metabolism, distinct from the loss of eIF5AHyp. To test this hypothesis, we utilized zebrafish and mouse models with inducible knockdowns of deoxyhypusine synthase (DHPS) and eIF5A to investigate their roles in cellular growth. Gene expression analysis via RNA sequencing and morphometric measurements of pancreas and β-cell mass were performed to assess phenotypic changes and identify affected biological pathways. Loss of DHPS in zebrafish resulted in significant defects in pancreatic growth, accompanied by changes in gene expression related to mRNA translation, neurogenesis, and stress pathways. By contrast, knockdown of eIF5A had minimal impact on pancreas development, suggesting that the effects of DHPS loss are not solely because of the lack of eIF5AHyp. In mice, β-cell-specific deletion of DHPS impaired β-cell mass expansion and glucose tolerance, whereas eIF5A deletion had no statistically significant effects. These findings provide evidence for an independent role for eIF5ALys in regulating developmental and functional responses in pancreas health and disease.

The Alteration of Proteomic Profiles in Hippocampus of Type 2 Diabetic Mice Associated With Cognitive Impairment

Clinical and experimental studies have demonstrated that type 2 diabetes mellitus (T2DM) affects the brain structure and function, in particular the hippocampus, leading to cognitive impairments. However, the molecular mechanisms underlying cognitive deficits induced by T2DM are not fully understood. In this study, we aimed to investigate the effects of T2DM on behavior, the proteome profile in the hippocampus, and the potential molecular pathways involved in the development of cognitive dysfunction in T2DM mice. We found that the diabetic mice exhibited cognitive impairment in the novel object location recognition test and the novel object recognition test. The proteomic analysis revealed that various molecular pathways were involved in this context. These included the upregulation of proteins in the protein synthesis and folding pathway (EIF5A, RSP24, and PPIB), endocytosis and cellular trafficking (VPS24, SNX12, and ARP2/3), cannabinoid receptor interacting (CRIP1), ubiquitination (SKP1), and oxidative stress response (NUDT3). Downregulated proteins were related to mitochondria function (ANT1), neuronal development (ELP1), protein glycosylation (RPN2), and endocytosis (VPS4). Our study shows that T2DM mice exhibit neurocognitive impairment, which is linked to the dysregulation of hippocampal proteins involved in various molecular pathways. These findings contribute to a better understanding of the pathophysiology of T2DM-related cognitive impairment and may identify molecular targets for drug development to treat T2DM-associated cognitive impairment conditions.

Insights into eukaryotic translation initiation factor 5A: Its role and mechanisms in protein synthesis

The protein synthesis within eukaryotic cells is a complex process involving various translation factors. Among these factors, eukaryotic translation initiation factor 5 A (eIF5A) emerges as a crucial translation factor with high evolutionary conservation. eIF5A is unique as it is the only protein in eukaryotic cells containing the hypusine modification. Initially presumed to be a translation initiation factor, eIF5A was subsequently discovered to act mainly during the translation elongation phase. Notably, eIF5A facilitates the translation of peptide sequences containing polyproline stretches and exerts a universal regulatory effect on the elongation and termination phases of protein synthesis. Additionally, eIF5A indirectly affects various physiological processes within the cell by modulating the translation of specific proteins. This review provides a comprehensive overview of the structure, physiological functions, various post-translational modifications of eIF5A, and its association with various human diseases. The comparison between eIF5A and its bacterial homolog, EF-P, extends the discussion to the evolutionary conservation of eIF5A. This highlights its significance across different domains of life.

Spermidine mediates acetylhypusination of RIPK1 to suppress diabetes onset and progression

It has been established that N-acetyltransferase (murine NAT1 (mNAT1) and human NAT2 (hNAT2)) mediates insulin sensitivity in type 2 diabetes. Here we show that mNAT1 deficiency leads to a decrease in cellular spermidine-a natural polyamine exhibiting health-protective and anti-ageing effects-but understanding of its mechanism is limited. We identify that mNAT1 and hNAT2 modulate a type of post-translational modification involving acetylated spermidine, which we name acetylhypusination, on receptor-interacting serine/threonine-protein kinase 1 (RIPK1)-a key regulator of inflammation and cell death. Spermidine supplementation decreases RIPK1-mediated cell death and diabetic phenotypes induced by NAT1 deficiency in vivo. Furthermore, insulin resistance and diabetic kidney disease mediated by vascular pathology in NAT1-deficient mice can be blocked by inhibiting RIPK1. Finally, we demonstrate a decrease in spermidine and activation of RIPK1 in the vascular tissues of human patients with diabetes. Our study suggests a role for vascular pathology in diabetes onset and progression and identifies the inhibition of RIPK1 kinase as a potential therapeutic approach for the treatment of type 2 diabetes.

Manipulation of DHPS activity affects dendritic morphology and expression of synaptic proteins in primary rat cortical neurons

Deoxyhypusine synthase (DHPS) catalyzes the initial step of hypusine incorporation into the eukaryotic initiation factor 5A (eIF5A), leading to its activation. The activated eIF5A, in turn, plays a key role in regulating the protein translation of selected mRNAs and therefore appears to be a suitable target for therapeutic intervention strategies. In the present study, we analyzed the role of DHPS-mediated hypusination in regulating neuronal homeostasis using lentivirus-based gain and loss of function experiments in primary cortical cultures from rats. This model allows us to examine the impact of DHPS function on the composition of the dendritic and synaptic compartments, which may contribute to a better understanding of cognitive function and neurodevelopment in vivo. Our findings revealed that shRNA-mediated DHPS knockdown diminishes the amount of hypusinated eIF5A (eIF5AHyp), resulting in notable alterations in neuronal dendritic architecture. Furthermore, in neurons, the synaptic composition was also affected, showing both pre- and post-synaptic changes, while the overexpression of DHPS had only a minor impact. Therefore, we hypothesize that interfering with the eIF5A hypusination caused by reduced DHPS activity impairs neuronal and synaptic homeostasis.

Deoxyhypusine synthase deficiency syndrome zebrafish model: aberrant morphology, epileptiform activity, and reduced arborization of inhibitory interneurons

DHPS deficiency syndrome is an ultra-rare neurodevelopmental disorder (NDD) which results from biallelic mutations in the gene encoding the enzyme deoxyhypusine synthase (DHPS). DHPS is essential to synthesize hypusine, a rare amino acid formed by post-translational modification of a conserved lysine in eukaryotic initiation factor 5 A (eIF5A). DHPS deficiency syndrome causes epilepsy, cognitive and motor impairments, and mild facial dysmorphology. In mice, a brain-specific genetic deletion of Dhps at birth impairs eIF5AHYP-dependent mRNA translation. This alters expression of proteins required for neuronal development and function, and phenotypically models features of human DHPS deficiency. We studied the role of DHPS in early brain development using a zebrafish loss-of-function model generated by knockdown of dhps expression with an antisense morpholino oligomer (MO) targeting the exon 2/intron 2 (E2I2) splice site of the dhps pre-mRNA. dhps knockdown embryos exhibited dose-dependent developmental delay and dysmorphology, including microcephaly, axis truncation, and body curvature. In dhps knockdown larvae, electrophysiological analysis showed increased epileptiform activity, and confocal microscopy analysis revealed reduced arborisation of GABAergic neurons. Our findings confirm that hypusination of eIF5A by DHPS is needed for early brain development, and zebrafish with an antisense knockdown of dhps model features of DHPS deficiency syndrome.

Spermidine-eIF5A axis is essential for muscle stem cell activation via translational control

Adult skeletal muscle stem cells, also known satellite cells (SCs), are quiescent and activate in response to injury. However, the activation mechanisms of quiescent SCs (QSCs) remain largely unknown. Here, we investigated the metabolic regulation of SC activation by identifying regulatory metabolites that promote SC activation. Using targeted metabolomics, we found that spermidine acts as a regulatory metabolite to promote SC activation and muscle regeneration in mice. Mechanistically, spermidine activates SCs via generating hypusinated eIF5A. Using SC-specific eIF5A-knockout (KO) and Myod-KO mice, we further found that eIF5A is required for spermidine-mediated SC activation by controlling MyoD translation. More significantly, depletion of eIF5A in SCs results in impaired muscle regeneration in mice. Together, the findings of our study define a novel mechanism that is essential for SC activation and acts via spermidine-eIF5A-mediated MyoD translation. Our findings suggest that the spermidine-eIF5A axis represents a promising pharmacological target in efforts to activate endogenous SCs for the treatment of muscular disease.

Integrative Analysis of Morphine-Induced Differential Circular RNAs and ceRNA Networks in the Medial Prefrontal Cortex

Circular RNAs (circRNAs) are a novel type of non-coding RNAs. Despite the fact that the functional mechanisms of most circRNAs remain unknown, emerging evidence indicates that circRNAs could sponge microRNAs (miRNAs), bind to RNA binding proteins (RBP), and even be translated into protein. Recent research has demonstrated the crucial roles played by circRNAs in neuropsychiatric disorders. The medial prefrontal cortex (mPFC) is a crucial component of drug reward circuitry and exerts top-down control over cognitive functions. However, there is currently limited knowledge about the correlation between circRNAs and morphine-associated contextual memory in the mPFC. Here, we performed morphine-induced conditioned place preference (CPP) in mice and extracted mPFC tissue for RNA-sequencing. Our study represented the first attempt to identify differentially expressed circRNAs (DEcircRNAs) and mRNAs (DEmRNAs) in the mPFC after morphine-induced CPP. We identified 47 significantly up-regulated DEcircRNAs and 429 significantly up-regulated DEmRNAs, along with 74 significantly down-regulated DEcircRNAs and 391 significantly down-regulated DEmRNAs. Functional analysis revealed that both DEcircRNAs and DEmRNAs were closely associated with neuroplasticity. To further validate the DEcircRNAs, we conducted qRT-PCR, Sanger sequencing, and RNase R digestion assays. Additionally, using an integrated bioinformatics approach, we constructed ceRNA networks and identified critical circRNA/miRNA/mRNA axes that contributed to the development of morphine-associated contextual memory. In summary, our study provided novel insights into the role of circRNAs in drug-related memory, specifically from the perspective of ceRNAs.

A Translational Regulatory Mechanism Mediated by Hypusinated Eukaryotic Initiation Factor 5A Facilitates β-Cell Identity and Function

As professional secretory cells, β-cells require adaptable mRNA translation to facilitate a rapid synthesis of proteins, including insulin, in response to changing metabolic cues. Specialized mRNA translation programs are essential drivers of cellular development and differentiation. However, in the pancreatic β-cell, the majority of factors identified to promote growth and development function primarily at the level of transcription. Therefore, despite its importance, the regulatory role of mRNA translation in the formation and maintenance of functional β-cells is not well defined. In this study, we have identified a translational regulatory mechanism mediated by the specialized mRNA translation factor eukaryotic initiation factor 5A (eIF5A), which facilitates the maintenance of β-cell identity and function. The mRNA translation function of eIF5A is only active when it is posttranslationally modified ("hypusinated") by the enzyme deoxyhypusine synthase (DHPS). We have discovered that the absence of β-cell DHPS in mice reduces the synthesis of proteins critical to β-cell identity and function at the stage of β-cell maturation, leading to a rapid and reproducible onset of diabetes. Therefore, our work has revealed a gatekeeper of specialized mRNA translation that permits the β-cell, a metabolically responsive secretory cell, to maintain the integrity of protein synthesis necessary during times of induced or increased demand.

ARTICLE HIGHLIGHTS

Prognostic value and immunological role of PD-L1 gene in pan-cancer

OBJECTIVE

PD-L1, a target of immune checkpoint blockade, has been proven to take the role of an oncogene in most human tumors. However, the role of PD-L1 in human pan-cancers has not yet been fully investigated.

MATERIALS AND METHODS

Pan-cancer analysis was conducted to analyze expression, genetic alterations, prognosis analysis, and immunological characteristics of PD-L1. Estimating the correlation between PD-L1 expression and survival involved using pooled odds ratios and hazard ratios with 95% CI. The Kaplan-Meier (K-M) technique, COX analysis, and receiver operating characteristic (ROC) curves were applied to the survival analysis. Additionally, we investigated the relationships between PD-L1 and microsatellite instability (MSI), tumor mutational burden (TMB), DNA methyltransferases (DNMTs), the associated genes of mismatch repair (MMR), and immune checkpoint biomarkers using Spearman's correlation analysis. Also, immunohistochemical analysis and qRT-PCR were employed in evaluating PD-L1's protein and mRNA expression in pan-caner.

RESULTS

PD-L1 showed abnormal mRNA and protein expression in a variety of cancers and predicted prognosis in cancer patients. Furthermore, across a variety of cancer types, the aberrant PD-L1 expression was connected to the MSI, MMR, TMB, drug sensitivity, and tumor immune microenvironment (TIME). Moreover, PD-L1 was significantly correlated with infiltrating levels of immune cells (T cell CD8 + , neutrophil, and so on).

CONCLUSION

Our study provides a better theoretical basis and guidance for the clinical treatment of PD-L1.

Expression profiles and function prediction of tRNA-derived fragments in glioma

BACKGROUND

Glioblastoma (GBM) is the most aggressive malignant primary brain tumor. The transfer RNA-derived fragments (tRFs) are a new group of small noncoding RNAs, which are dysregulated in many cancers. Until now, the expression and function of tRFs in glioma remain unknown.

METHODS

The expression profiles of tRF subtypes were analyzed using the Cancer Genome Atlas (TCGA)-low-grade gliomas (LGG)/GBM dataset. The target genes of tRFs were subjected to Gene Ontology, Kyoto Encyclopedia and Gene set enrichment analysis of Genes and Genomes pathway enrichment analysis. The protein-protein interaction enrichment analysis was performed by STRING. QRT-PCR was performed to detect the expressions of tRFs in human glioma cell lines U87, U373, U251, and human astrocyte cell line SVG p12. Western blot assay was used to detect to the expression of S100A11. The interaction between tRF-19-R118LOJX and S100A11 mRNA 3'UTR was detected by dual-luciferase reporter assay. The effects of tRF-19-R118LOJX, tRF-19-6SM83OJX and S100A11 on the glioma cell proliferation, migration and in vitro vasculogenic mimicry formation ability were examined by CCK-8 proliferation assay, EdU assay, HoloMonitor cell migration assay and tube formation assay, respectively.

RESULTS

tRF-19-R118LOJX and tRF-19-6SM83OJX are the most differentially expressed tRFs between LGG and GBM groups. The functional enrichment analysis showed that the target genes of tRF-19-R118LOJX and tRF-19-6SM83OJX are enriched in regulating blood vessel development. The upregulated target genes are linked to adverse survival outcomes in glioma patients. tRF-19-R118LOJX and tRF-19-6SM83OJX were identified to suppress glioma cell proliferation, migration, and in vitro vasculogenic mimicry formation. The mechanism of tRF-19-R118LOJX might be related to its function as an RNA silencer by targeting the S100A11 mRNA 3'UTR.

CONCLUSION

tRFs would become novel diagnostic biomarkers and therapeutic targets of glioma, and the mechanism might be related to its post-transcriptionally regulation of gene expression by targeting mRNA 3'UTR.

Neuronal RBM5 modulates cell signaling responses to traumatic and hypoxic-ischemic injury in a sex-dependent manner

It is not clear if inhibiting the pro-death gene RNA binding motif 5 (RBM5) is neuroprotective in isolated primary neurons or if it regulates cell survival in a sex-dependent manner. Here we established sex-dichotomized primary cortical neuron cultures from transgenic mice harboring a floxed RBM5 gene-trap. Lentivirus-mediated expression of CRE was used to silence RBM5 expression. Male and female neurons were maintained in next-generation Neurobasal-Plus media and subjected to a mechanical stretch-injury (to model traumatic brain injury) or oxygen-glucose deprivation/OGD (to model ischemia). RBM5 KO did not affect 24 h post-injury survival as determined by lactate dehydrogenase (LDH) release, in either paradigm. In contrast, female KO neurons had increased spectrin breakdown products post-insult (in both models). Furthermore, in OGD, RBM5 KO in male neurons exacerbated injury-induced downregulation of pro-survival AKT activation (pAKT473) but conversely led to pAKT473 sparing in female neurons. Moreover, global proteomics identified 19 differentially expressed (DE) proteins in OGD-injured male neurons, and 102 DE proteins in injured female neurons. Two novel RBM5-regulated proteins (PIGQ and EST1C) were identified in injured male KO neurons, and 8 novel proteins identified in injured female KO neurons (S35A5, DHTK1, STX3, IF3M, RN167, K1C14, DYHS, and MED13). In summary, RBM5 inhibition does not modify neuronal survival in primary mouse neurons in 2 clinically relevant models of excitotoxic insult, but RBM5 does regulate intracellular responses to injury in a sex-dependent manner.

Multiphase CT radiomics nomogram for preoperatively predicting the WHO/ISUP nuclear grade of small (< 4 cm) clear cell renal cell carcinoma

BACKGROUND

Small (< 4 cm) clear cell renal cell carcinoma (ccRCC) is the most common type of small renal cancer and its prognosis is poor. However, conventional radiological characteristics obtained by computed tomography (CT) are not sufficient to predict the nuclear grade of small ccRCC before surgery.

METHODS

A total of 113 patients with histologically confirmed ccRCC were randomly assigned to the training set (n = 67) and the testing set (n = 46). The baseline and CT imaging data of the patients were evaluated statistically to develop a clinical model. A radiomics model was created, and the radiomics score (Rad-score) was calculated by extracting radiomics features from the CT images. Then, a clinical radiomics nomogram was developed using multivariate logistic regression analysis by combining the Rad-score and critical clinical characteristics. The receiver operating characteristic (ROC) curve was used to evaluate the discrimination of small ccRCC in both the training and testing sets.

RESULTS

The radiomics model was constructed using six features obtained from the CT images. The shape and relative enhancement value of the nephrographic phase (REV of the NP) were found to be independent risk factors in the clinical model. The area under the curve (AUC) values for the training and testing sets for the clinical radiomics nomogram were 0.940 and 0.902, respectively. Decision curve analysis (DCA) revealed that the radiomics nomogram model was a better predictor, with the highest degree of coincidence.

CONCLUSION

The CT-based radiomics nomogram has the potential to be a noninvasive and preoperative method for predicting the WHO/ISUP grade of small ccRCC.

Deubiquitinase OTUD3: a double-edged sword in immunity and disease

Deubiquitination is an important form of post-translational modification that regulates protein homeostasis. Ovarian tumor domain-containing proteins (OTUDs) subfamily member OTUD3 was identified as a deubiquitinating enzyme involved in the regulation of various physiological processes such as immunity and inflammation. Disturbances in these physiological processes trigger diseases in humans and animals, such as cancer, neurodegenerative diseases, diabetes, mastitis, etc. OTUD3 is aberrantly expressed in tumors and is a double-edged sword, exerting tumor-promoting or anti-tumor effects in different types of tumors affecting cancer cell proliferation, metastasis, and metabolism. OTUD3 is regulated at the transcriptional level by a number of MicroRNAs, such as miR-520h, miR-32, and miR101-3p. In addition, OTUD3 is regulated by a number of post-translational modifications, such as acetylation and ubiquitination. Therefore, understanding the regulatory mechanisms of OTUD3 expression can help provide insight into its function in human immunity and disease, offering the possibility of its use as a therapeutic target to diagnose or treat disease.

Deoxyhypusine synthase mutations alter the post-translational modification of eukaryotic initiation factor 5A resulting in impaired human and mouse neural homeostasis

DHPS deficiency is a rare genetic disease caused by biallelic hypomorphic variants in the Deoxyhypusine synthase (DHPS) gene. The DHPS enzyme functions in mRNA translation by catalyzing the post-translational modification, and therefore activation, of eukaryotic initiation factor 5A (eIF5A). The observed clinical outcomes associated with human mutations in DHPS include developmental delay, intellectual disability, and seizures. Therefore, to increase our understanding of this rare disease, it is critical to determine the mechanisms by which mutations in DHPS alter neurodevelopment. In this study, we have generated patient-derived lymphoblast cell lines and demonstrated that human DHPS variants alter DHPS protein abundance and impair enzyme function. Moreover, we observe a shift in the abundance of the post-translationally modified forms of eIF5A; specifically, an increase in the nuclear localized acetylated form (eIF5A^AcK47) and concomitant decrease in the cytoplasmic localized hypusinated form (eIF5A^HYP). Generation and characterization of a mouse model with a genetic deletion of Dhps in the brain at birth shows that loss of hypusine biosynthesis impacts neuronal function due to impaired eIF5A^HYP-dependent mRNA translation; this translation defect results in altered expression of proteins required for proper neuronal development and function. This study reveals new insight into the biological consequences and molecular impact of human DHPS deficiency and provides valuable information toward the goal of developing treatment strategies for this rare disease.

Deoxyhypusine synthase is required for the translational regulation of pancreatic beta cell maturation

As professional secretory cells, beta cells require adaptable mRNA translation to facilitate a rapid synthesis of proteins, including insulin, in response to changing metabolic cues. Specialized mRNA translation programs are essential drivers of cellular development and differentiation. However, in the pancreatic beta cell, the majority of factors identified to promote growth and development function primarily at the level of transcription. Therefore, despite its importance, the regulatory role of mRNA translation in the formation and maintenance of functional beta cells is not well defined. In this study, we have identified a translational regulatory mechanism in the beta cell driven by the specialized mRNA translation factor, eukaryotic initiation factor 5A (eIF5A), which facilitates beta cell maturation. The mRNA translation function of eIF5A is only active when it is post-translationally modified ("hypusinated") by the enzyme deoxyhypusine synthase (DHPS). We have discovered that the absence of beta cell DHPS in mice reduces the synthesis of proteins critical to beta cell identity and function at the stage of beta cell maturation, leading to a rapid and reproducible onset of diabetes. Therefore, our work has revealed a gatekeeper of specialized mRNA translation that permits the beta cell, a metabolically responsive secretory cell, to maintain the integrity of protein synthesis necessary during times of induced or increased demand.

ARTICLE HIGHLIGHTS

Pancreatic beta cells are professional secretory cells that require adaptable mRNA translation for the rapid, inducible synthesis of proteins, including insulin, in response to changing metabolic cues. Our previous work in the exocrine pancreas showed that development and function of the acinar cells, which are also professional secretory cells, is regulated at the level of mRNA translation by a specialized mRNA translation factor, eIF5A ^HYP . We hypothesized that this translational regulation, which can be a response to stress such as changes in growth or metabolism, may also occur in beta cells. Given that the mRNA translation function of eIF5A is only active when the factor is post-translationally modified ("hypusinated") by the enzyme deoxyhypusine synthase (DHPS), we asked the question: does DHPS/eIF5A ^HYP regulate the formation and maintenance of functional beta cells? We discovered that in the absence of beta cell DHPS in mice, eIF5A is not hypusinated (activated), which leads to a reduction in the synthesis of critical beta cell proteins that interrupts pathways critical for identity and function. This translational regulation occurs at weaning age, which is a stage of cellular stress and maturation for the beta cell. Therefore without DHPS/eIF5A ^HYP , beta cells do not mature and mice progress to hyperglycemia and diabetes. Our findings suggest that secretory cells have a mechanism to regulate mRNA translation during times of cellular stress. Our work also implies that driving an increase in mRNA translation in the beta cell might overcome or possibly reverse the beta cell defects that contribute to early dysfunction and the progression to diabetes.

Cryo-EM structure of human eIF5A-DHS complex reveals the molecular basis of hypusination-associated neurodegenerative disorders

Hypusination is a unique post-translational modification of the eukaryotic translation factor 5A (eIF5A) that is essential for overcoming ribosome stalling at polyproline sequence stretches. The initial step of hypusination, the formation of deoxyhypusine, is catalyzed by deoxyhypusine synthase (DHS), however, the molecular details of the DHS-mediated reaction remained elusive. Recently, patient-derived variants of DHS and eIF5A have been linked to rare neurodevelopmental disorders. Here, we present the cryo-EM structure of the human eIF5A-DHS complex at 2.8 Å resolution and a crystal structure of DHS trapped in the key reaction transition state. Furthermore, we show that disease-associated DHS variants influence the complex formation and hypusination efficiency. Hence, our work dissects the molecular details of the deoxyhypusine synthesis reaction and reveals how clinically-relevant mutations affect this crucial cellular process.

New K50R mutant mouse models reveal impaired hypusination of eif5a2 with alterations in cell metabolite landscape

The eukaryotic translation initiation factor 5A1 (eIF5A1) and 5A2 (eIF5A2) are important proteins in a variety of physiological and pathophysiological processes and their function has been linked to neurodevelopmental disorders, cancer, and viral infections. Here, we report two new genome-edited mouse models, generated using a CRISPR-Cas9 approach, in which the amino acid residue lysine 50 is replaced with arginine 50 (K50R) in eIF5A1 or in the closely related eIF5A2 protein. This mutation prevents the spermidine-dependent post-translational formation of hypusine, a unique lysine derivative that is necessary for activation of eIF5A1 and eIF5A2. Mouse brain lysates from homozygous eif5a2-K50R mutant mice (eif5a2K50R/K50R) confirmed the absence of hypusine formation of eIF5A2, and metabolomic analysis of primary mouse dermal fibroblasts revealed significant alterations in the metabolite landscape compared to controls including increased levels of tryptophan, kyrunenine, pyridoxine, nicotinamide adenine dinucleotide, riboflavin, flavin adenine dinucleotide, pantothenate, and coenzyme A. Further supported by new publicly available bioinformatics data, these new mouse models represent excellent in vivo models to study hypusine-dependent biological processes, hypusination-related disorders caused by eIF5A1 and eIF5A2 gene aberrations or mRNA expression dysregulation, as well as several major human cancer types and potential therapies.

Mechanisms of spermidine-induced autophagy and geroprotection

Aging involves the systemic deterioration of all known cell types in most eukaryotes. Several recently discovered compounds that extend the healthspan and lifespan of model organisms decelerate pathways that govern the aging process. Among these geroprotectors, spermidine, a natural polyamine ubiquitously found in organisms from all kingdoms, prolongs the lifespan of fungi, nematodes, insects and rodents. In mice, it also postpones the manifestation of various age-associated disorders such as cardiovascular disease and neurodegeneration. The specific features of spermidine, including its presence in common food items, make it an interesting candidate for translational aging research. Here, we review novel insights into the geroprotective mode of action of spermidine at the molecular level, as we discuss strategies for elucidating its clinical potential.

Conditional deletion of MAD2B in forebrain neurons enhances hippocampus-dependent learning and memory in mice

Mitotic arrest deficient 2-like protein 2 (MAD2B) is not only a DNA damage repair agent but also a cell cycle regulator that is widely expressed in the hippocampus and the cerebral cortex. However, the functions of MAD2B in hippocampal and cerebral cortical neurons are poorly understood. In this study, we crossed MAD2Bflox/flox and calcium/calmodulin-dependent protein kinase II alpha (Camk2a)-Cre mice to conditionally knock out MAD2B in the forebrain pyramidal neurons by the Cre/loxP recombinase system. First, RNA sequencing suggested that the differentially expressed genes in the hippocampus and the cerebral cortex between the WT and the MAD2B cKO mice were related to learning and memory. Then, the results of behavioral tests, including the Morris water maze test, the novel object recognition test, and the contextual fear conditioning experiment, suggested that the learning and memory abilities of the MAD2B cKO mice had improved. Moreover, conditional knockout of MAD2B increased the number of neurons without affecting the number of glial cells in the hippocampal CA1 and the cerebral cortex. At the same time, the number of doublecortin-positive (DCX+) cells was increased in the dentate gyrus (DG) of the MAD2B cKO mice. In addition, as shown by Golgi staining, the MAD2B cKO mice had more mushroom-like and long-like spines than the WT mice. Transmission electron microscopy (TEM) revealed that spine synapses increased and shaft synapses decreased in the CA1 of the MAD2B cKO mice. Taken together, our findings indicated that MAD2B plays an essential role in regulating learning and memory.

Bi-allelic variants in DOHH, catalyzing the last step of hypusine biosynthesis, are associated with a neurodevelopmental disorder

Deoxyhypusine hydroxylase (DOHH) is the enzyme catalyzing the second step in the post-translational synthesis of hypusine [N^ε-(4-amino-2-hydroxybutyl)lysine] in the eukaryotic initiation factor 5A (eIF5A). Hypusine is formed exclusively in eIF5A by two sequential enzymatic steps catalyzed by deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Hypusinated eIF5A is essential for translation and cell proliferation in eukaryotes, and all three genes encoding eIF5A, DHPS, and DOHH are highly conserved throughout eukaryotes. Pathogenic variants affecting either DHPS or EIF5A have been previously associated with neurodevelopmental disorders. Using trio exome sequencing, we identified rare bi-allelic pathogenic missense and truncating DOHH variants segregating with disease in five affected individuals from four unrelated families. The DOHH variants are associated with a neurodevelopmental phenotype that is similar to phenotypes caused by DHPS or EIF5A variants and includes global developmental delay, intellectual disability, facial dysmorphism, and microcephaly. A two-dimensional gel analyses revealed the accumulation of deoxyhypusine-containing eIF5A [eIF5A(Dhp)] and a reduction in the hypusinated eIF5A in fibroblasts derived from affected individuals, providing biochemical evidence for deficiency of DOHH activity in cells carrying the bi-allelic DOHH variants. Our data suggest that rare bi-allelic variants in DOHH result in reduced enzyme activity, limit the hypusination of eIF5A, and thereby lead to a neurodevelopmental disorder.

Eukaryotic Initiation Factor 5A2 Regulates Expression of Antiviral Genes

Translation factors are essential for regulation of protein synthesis. The eukaryotic translation initiation factor 5A (eIF5A) family is made up of two paralogues - eIF5A1 and eIF5A2 - which display high sequence homology but distinct tissue tropism. While eIF5A1 directly binds to the ribosome and regulates translation initiation, elongation, and termination, the molecular function of eIF5A2 remains poorly understood. Here, we engineer an eIF5A2 knockout allele in the SW480 colon cancer cell line. Using ribosome profiling and RNA-Sequencing, we reveal that eIF5A2 is functionally distinct from eIF5A1 and does not regulate transcript-specific or global protein synthesis. Instead, eIF5A2 knockout leads to decreased intrinsic antiviral gene expression, including members of the IFITM and APOBEC3 family. Furthermore, cells lacking eIF5A2 display increased permissiveness to virus infection. Our results uncover eIF5A2 as a factor involved regulating the antiviral transcriptome, and reveal an example of how gene duplications of translation factors can result in proteins with distinct functions.

The eukaryotic initiation factor 5A (eIF5A1), the molecule, mechanisms and recent insights into the pathophysiological roles

Since the demonstration of its involvement in cell proliferation, the eukaryotic initiation factor 5A (eIF5A) has been studied principally in relation to the development and progression of cancers in which the isoform A2 is mainly expressed. However, an increasing number of studies report that the isoform A1, which is ubiquitously expressed in normal cells, exhibits novel molecular features that reveal its new relationships between cellular functions and organ homeostasis. At a first glance, eIF5A can be regarded, among other things, as a factor implicated in the initiation of translation. Nevertheless, at least three specificities: (1) its extreme conservation between species, including plants, throughout evolution, (2) its very special and unique post-translational modification through the activating-hypusination process, and finally (3) its close relationship with the polyamine pathway, suggest that the role of eIF5A in living beings remains to be uncovered. In fact, and beyond its involvement in facilitating the translation of proteins containing polyproline residues, eIF5A is implicated in various physiological processes including ischemic tolerance, metabolic adaptation, aging, development, and immune cell differentiation. These newly discovered physiological properties open up huge opportunities in the clinic for pathologies such as, for example, the ones in which the oxygen supply is disrupted. In this latter case, organ transplantation, myocardial infarction or stroke are concerned, and the current literature defines eIF5A as a new drug target with a high level of potential benefit for patients with these diseases or injuries. Moreover, the recent use of genomic and transcriptomic association along with metadata studies also revealed the implication of eIF5A in genetic diseases. Thus, this review provides an overview of eIF5A from its molecular mechanism of action to its physiological roles and the clinical possibilities that have been recently reported in the literature.