Meprin ß knockout reduces brain Aß levels and rescues learning and memory impairments in the APP/lon mouse model for Alzheimer's disease.

ß-Site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) is the major described ß-secretase to generate Aß peptides in Alzheimer's disease (AD). However, all therapeutic attempts to block BACE1 activity and to improve AD symptoms have so far failed. A potential candidate for alternative Aß peptides generation is the metalloproteinase meprin ß, which cleaves APP predominantly at alanine in p2 and in this study we can detect an increased meprin ß expression in AD brain. Here, we report the generation of the transgenic APP/lon mouse model of AD lacking the functional Mep1b gene (APP/lon × Mep1b-/-). We examined levels of canonical and truncated Aß species using urea-SDS-PAGE, ELISA and immunohistochemistry in brains of APP/lon mouse × Mep1b-/-. Additionally, we investigated the cognitive abilities of these mice during the Morris water maze task. Aß1-40 and 1-42 levels are reduced in APP/lon mice when meprin ß is absent. Immunohistochemical staining of mouse brain sections revealed that N-terminally truncated Aß2-x peptide deposition is decreased in APP/lon × Mep1b-/- mice. Importantly, loss of meprin ß improved cognitive abilities and rescued learning behavior impairments in APP/lon mice. These observations indicate an important role of meprin ß within the amyloidogenic pathway and Aß production in vivo.

Metabolic control of adult neural stem cell self-renewal by the mitochondrial protease YME1L.

The transition between quiescence and activation in neural stem and progenitor cells (NSPCs) is coupled with reversible changes in energy metabolism with key implications for lifelong NSPC self-renewal and neurogenesis. How this metabolic plasticity is ensured between NSPC activity states is unclear. We find that a state-specific rewiring of the mitochondrial proteome by the i-AAA peptidase YME1L is required to preserve NSPC self-renewal. YME1L controls the abundance of numerous mitochondrial substrates in quiescent NSPCs, and its deletion activates a differentiation program characterized by broad metabolic changes causing the irreversible shift away from a fatty-acid-oxidation-dependent state. Conditional Yme1l deletion in adult NSPCs in vivo results in defective self-renewal and premature differentiation, ultimately leading to NSPC pool depletion. Our results disclose an important role for YME1L in coordinating the switch between metabolic states of NSPCs and suggest that NSPC fate is regulated by compartmentalized changes in protein network dynamics.

Deficiency of Nardilysin in the Liver Reduces Serum Cholesterol Levels.

Nardilysin (NRDC) has been shown to be involved in post-translational histone modifications, in addition to enhancement in ectodomain shedding of membrane-anchored protein, which play significant roles in various pathophysiology, including glucose homeostasis, inflammatory diseases and cancer. The present study sought to determine roles of NRDC in the liver on lipid and lipoprotein metabolism. We established liver-specific NRDC deficient mice by use of NRD1 floxed mice and albumin promoter-Cre recombinase (Cre) transgenic mice, and found that their serum low-density lipoprotein (LDL) cholesterol levels were significantly lower than those in control littermate mice. In the liver, LDL receptor (LDLR) mRNA expression was significantly upregulated, while inducible degrader of LDLR (IDOL) and microsomal triglyceride transfer protein (MTP) mRNA expression was significantly downregulated, in liver-specific NRDC deficient mice. Hepatic cell-surface LDLR expression levels were significantly elevated and serum pro-protein convertase subtilisin-kexin type 9 (PCSK9) levels were significantly reduced in mice with hepatic NRDC deficiency. In cultured hepatocytes, NRDC deficiency significantly reduced secreted PCSK9 and increased cell-surface LDLR expression. On the other hand, NRDC overexpression in cultured hepatocytes significantly increased secreted PCSK9 and lowered cell-surface LDLR expression. Thus, NRDC in murine hepatocytes appears to play key roles in cholesterol homeostasis, although the precise molecular mechanisms remain to be determined.

Targeting RAS-converting enzyme 1 overcomes senescence and improves progeria-like phenotypes of ZMPSTE24 deficiency.

Several progeroid disorders are caused by deficiency in the endoprotease ZMPSTE24 which leads to accumulation of prelamin A at the nuclear envelope. ZMPSTE24 cleaves prelamin A twice: at the third carboxyl-terminal amino acid following farnesylation of a -CSIM motif; and 15 residues upstream to produce mature lamin A. The carboxyl-terminal cleavage can also be performed by RAS-converting enzyme 1 (RCE1) but little is known about the importance of this cleavage for the ability of prelamin A to cause disease. Here, we found that knockout of RCE1 delayed senescence and increased proliferation of ZMPSTE24-deficient fibroblasts from a patient with non-classical Hutchinson-Gilford progeria syndrome (HGPS), but did not influence proliferation of classical LMNA-mutant HGPS cells. Knockout of Rce1 in Zmpste24-deficient mice at postnatal week 4-5 increased body weight and doubled the median survival time. The absence of Rce1 in Zmpste24-deficient fibroblasts did not influence nuclear shape but reduced an interaction between prelamin A and AKT which activated AKT-mTOR signaling and was required for the increased proliferation. Prelamin A levels increased in Rce1-deficient cells due to a slower turnover rate but its localization at the nuclear rim was unaffected. These results strengthen the idea that the presence of misshapen nuclei does not prevent phenotype improvement and suggest that targeting RCE1 might be useful for treating the rare progeroid disorders associated with ZMPSTE24 deficiency.

Nardilysin controls cardiac sympathetic innervation patterning through regulation of p75 neurotrophin receptor.

Cardiac sympathetic innervation is critically involved in the regulation of circulatory dynamics. However, the molecular mechanism for the innervation patterning has remained elusive. Here, we demonstrate that nardilysin (NRDC, Nrdc), an enhancer of ectodomain shedding, regulates cardiac sympathetic innervation. Nardilysin-deficient (Nrdc-/- ) mice show hypoplastic hearts, hypotension, bradycardia, and abnormal sympathetic innervation patterning. While the innervation of left ventricle (LV) of wild-type mice is denser in the subepicardium than in the subendocardium, Nrdc-/- LV lacks such a polarity and is uniformly and more abundantly innervated. At the molecular level, the full-length form of p75 neurotrophin receptor (p75NTR , Ngfr) is increased in Nrdc-/- LV due to the reduced ectodomain shedding of p75NTR . Importantly, the reduction of p75NTR rescued the abnormal innervation phenotype of Nrdc-/- mice. Moreover, sympathetic neuron-specific, but not cardiomyocyte-specific deletion of Nrdc recapitulated the abnormal innervation patterning of Nrdc-/- mice. In conclusion, neuronal nardilysin critically regulates cardiac sympathetic innervation and circulatory dynamics via modulation of p75NTR .

Staphylococcus aureus Fatty Acid Kinase FakA Modulates Pathogenesis during Skin Infection via Proteases.

Staphylococcus aureus fatty acid kinase FakA is necessary for the incorporation of exogenous fatty acids into the lipid membrane. We previously demonstrated that the inactivation of fakA leads to decreased α-hemolysin (Hla) production but increased expression of the proteases SspAB and aureolysin in vitro, and that the ΔfakA mutant causes larger lesions than the wild type (WT) during murine skin infection. As expected, necrosis is Hla dependent in the presence or absence of FakA, as both hla and hla ΔfakA mutants are unable to cause necrosis of the skin. At day 4 postinfection, while the ΔfakA mutant maintains larger and more necrotic abscesses, bacterial numbers are similar to those of the WT, indicating the enhanced tissue damage of mice infected with the ΔfakA mutant is not due to an increase in bacterial burden. At this early stage of infection, skin infected with the ΔfakA mutant has decreased levels of proinflammatory cytokines, such as interleukin-17A (IL-17A) and IL-1α, compared to those of WT-infected skin. At a later stage of infection (day 7), abscess resolution and bacterial clearance are hindered in ΔfakA mutant-infected mice. The paradoxical findings of decreased Hla in vitro but increased necrosis in vivo led us to investigate the role of the proteases regulated by FakA. Utilizing Δaur and ΔsspAB mutants in both the WT and fakA mutant backgrounds, we found that the absence of these proteases in a fakA mutant reduced dermonecrosis to levels similar to those of the WT strain. These studies suggest that the overproduction of proteases is one factor contributing to the enhanced pathogenesis of the ΔfakA mutant during skin infection.

Meprin-ß activity modulates the ß-catalytic subunit of protein kinase A in ischemia-reperfusion-induced acute kidney injury.

Meprin metalloproteases have been implicated in the progression of kidney injury. Previous work from our group has shown that meprins proteolytically process the catalytic subunit of protein kinase A (PKA-C), resulting in decreased PKA-C kinase activity. The goal of the present study was to determine the PKA-C isoforms impacted by meprin-ß and whether meprin-ß expression affects downstream mediators of the PKA signaling pathway in ischemia-reperfusion (IR)-induced kidney injury. IR was induced in 12-wk-old male wild-type (WT) and meprin-ß knockout (ßKO) mice. Madin-Darby canine kidney cells transfected with meprin-ß cDNA were also subjected to 2 h of hypoxia. Western blot analysis was used to evaluate levels of total PKA-C, PKA-Cα, PKA-Cß, phosphorylated (p-)PKA-C, and p-ERK1/2. Meprin-ß expression enhanced kidney injury as indicated by levels of neutrophil gelatinase-associated lipocalin and cystatin C. IR-associated decreases were observed in levels of p-PKA-C in kidney tissue from WT mice but not ßKO mice, suggesting that meprin-ß expression/activity is responsible for the in vivo reduction in kinase activity. Significant increases in levels of PKA-Cß were observed in kidney lysates for WT mice but not ßKO mice at 6 h post-IR. Proximal tubule PKA-Cß increases in WT but not ßKO kidneys were demonstrated by fluorescent microscopy. Furthermore, IR-induced injury was associated with significant increases in p-ERK levels for both genotypes. The present data demonstrate that meprin-ß enhances IR-induced kidney injury in part by modulating mediators of the PKA-Cß signaling pathway.

Deficiency in ZMPSTE24 and resulting farnesyl-prelamin A accumulation only modestly affect mouse adipose tissue stores.

Zinc metallopeptidase STE24 (ZMPSTE24) is essential for the conversion of farnesyl-prelamin A to mature lamin A, a key component of the nuclear lamina. In the absence of ZMPSTE24, farnesyl-prelamin A accumulates in the nucleus and exerts toxicity, causing a variety of disease phenotypes. By ∼4 months of age, both male and female Zmpste24-/- mice manifest a near-complete loss of adipose tissue, but it has never been clear whether this phenotype is a direct consequence of farnesyl-prelamin A toxicity in adipocytes. To address this question, we generated a conditional knockout Zmpste24 allele and used it to create adipocyte-specific Zmpste24-knockout mice. To boost farnesyl-prelamin A levels, we bred in the "prelamin A-only" Lmna allele. Gene expression, immunoblotting, and immunohistochemistry experiments revealed that adipose tissue in these mice had decreased Zmpste24 expression along with strikingly increased accumulation of prelamin A. In male mice, Zmpste24 deficiency in adipocytes was accompanied by modest changes in adipose stores (an 11% decrease in body weight, a 23% decrease in body fat mass, and significantly smaller gonadal and inguinal white adipose depots). No changes in adipose stores were detected in female mice, likely because prelamin A expression in adipose tissue is lower in female mice. Zmpste24 deficiency in adipocytes did not alter the number of macrophages in adipose tissue, nor did it alter plasma levels of glucose, triglycerides, or fatty acids. We conclude that ZMPSTE24 deficiency in adipocytes, and the accompanying accumulation of farnesyl-prelamin A, reduces adipose tissue stores, but only modestly and only in male mice.

Thimet Oligopeptidase (EC 3.4.24.15) Key Functions Suggested by Knockout Mice Phenotype Characterization.

Thimet oligopeptidase (THOP1) is thought to be involved in neuropeptide metabolism, antigen presentation, neurodegeneration, and cancer. Herein, the generation of THOP1 C57BL/6 knockout mice (THOP1-/-) is described showing that they are viable, have estrus cycle, fertility, and a number of puppies per litter similar to C57BL/6 wild type mice (WT). In specific brain regions, THOP1-/- exhibit altered mRNA expression of proteasome beta5, serotonin 5HT2a receptor and dopamine D2 receptor, but not of neurolysin (NLN). Peptidomic analysis identifies differences in intracellular peptide ratios between THOP1-/- and WT mice, which may affect normal cellular functioning. In an experimental model of multiple sclerosis THOP1-/- mice present worse clinical behavior scores compared to WT mice, corroborating its possible involvement in neurodegenerative diseases. THOP1-/- mice also exhibit better survival and improved behavior in a sepsis model, but also a greater peripheral pain sensitivity measured in the hot plate test after bradykinin administration in the paw. THOP1-/- mice show depressive-like behavior, as well as attention and memory retention deficits. Altogether, these results reveal a role of THOP1 on specific behaviors, immune-stimulated neurodegeneration, and infection-induced inflammation.

Astrocyte-specific deletion of the mitochondrial m-AAA protease reveals glial contribution to neurodegeneration.

Mitochondrial dysfunction causes neurodegeneration but whether impairment of mitochondrial homeostasis in astrocytes contributes to this pathological process remains largely unknown. The m-AAA protease exerts quality control and regulatory functions crucial for mitochondrial homeostasis. AFG3L2, which encodes one of the subunits of the m-AAA protease, is mutated in spinocerebellar ataxia SCA28 and in infantile syndromes characterized by spastic-ataxia, epilepsy and premature death. Here, we investigate the role of Afg3l2 and its redundant homologue Afg3l1 in the Bergmann glia (BG), radial astrocytes of the cerebellum that have functional connections with Purkinje cells (PC) and regulate glutamate homeostasis. We show that astrocyte-specific deletion of Afg3l2 in the mouse leads to late-onset motor impairment and to degeneration of BG, which display aberrant morphology, altered expression of the glutamate transporter EAAT2, and a reactive inflammatory signature. The neurological and glial phenotypes are drastically exacerbated when astrocytes lack both Afg31l and Afg3l2, and therefore, are totally depleted of the m-AAA protease. Moreover, mitochondrial stress responses and necroptotic markers are induced in the cerebellum. In both mouse models, targeted BG show a fragmented mitochondrial network and loss of mitochondrial cristae, but no signs of respiratory dysfunction. Importantly, astrocyte-specific deficiency of Afg3l1 and Afg3l2 triggers secondary morphological degeneration and electrophysiological changes in PCs, thus demonstrating a non-cell-autonomous role of glia in neurodegeneration. We propose that astrocyte dysfunction amplifies both neuroinflammation and glutamate excitotoxicity in patients carrying mutations in AFG3L2, leading to a vicious circle that contributes to neuronal death.

Loss of the mitochondrial i-AAA protease YME1L leads to ocular dysfunction and spinal axonopathy.

Disturbances in the morphology and function of mitochondria cause neurological diseases, which can affect the central and peripheral nervous system. The i-AAA protease YME1L ensures mitochondrial proteostasis and regulates mitochondrial dynamics by processing of the dynamin-like GTPase OPA1. Mutations in YME1L cause a multi-systemic mitochondriopathy associated with neurological dysfunction and mitochondrial fragmentation but pathogenic mechanisms remained enigmatic. Here, we report on striking cell-type-specific defects in mice lacking YME1L in the nervous system. YME1L-deficient mice manifest ocular dysfunction with microphthalmia and cataracts and develop deficiencies in locomotor activity due to specific degeneration of spinal cord axons, which relay proprioceptive signals from the hind limbs to the cerebellum. Mitochondrial fragmentation occurs throughout the nervous system and does not correlate with the degenerative phenotype. Deletion of Oma1 restores tubular mitochondria but deteriorates axonal degeneration in the absence of YME1L, demonstrating that impaired mitochondrial proteostasis rather than mitochondrial fragmentation causes the observed neurological defects.

Next-Generation Sequencing and Quantitative Proteomics of Hutchinson-Gilford progeria syndrome-derived cells point to a role of nucleotide metabolism in premature aging.

Hutchinson-Gilford progeria syndrome (HGPS) is a very rare fatal disease characterized for accelerated aging. Although the causal agent, a point mutation in LMNA gene, was identified more than a decade ago, the molecular mechanisms underlying HGPS are still not fully understood and, currently, there is no cure for the patients, which die at a mean age of thirteen. With the aim of unraveling non-previously altered molecular pathways in the premature aging process, human cell lines from HGPS patients and from healthy parental controls were studied in parallel using Next-Generation Sequencing (RNAseq) and High-Resolution Quantitative Proteomics (iTRAQ) techniques. After selection of significant proteins and transcripts and crosschecking of the results a small set of protein/transcript pairs were chosen for validation. One of those proteins, ribose-phosphate pyrophosphokinase 1 (PRPS1), is essential for nucleotide synthesis. PRPS1 loss-of-function mutants present lower levels of purine. PRPS1 protein and transcript levels are detected as significantly decreased in HGPS cell lines vs. healthy parental controls. This modulation was orthogonally confirmed by targeted techniques in cell lines and also in an animal model of Progeria, the ZMPSTE24 knock-out mouse. In addition, functional experiments through supplementation with S-adenosyl-methionine (SAMe), a metabolite that is an alternative source of purine, were done. Results indicate that SAMe has a positive effect in the proliferative capacity and reduces senescence-associated Beta-galactosidase staining of the HPGS cell lines. Altogether, our data suggests that nucleotide and, specifically, purine-metabolism, are altered in premature aging, opening a new window for the therapeutic treatment of the disease.

Aspergillus fumigatus conidial metalloprotease Mep1p cleaves host complement proteins.

Innate immunity in animals including humans encompasses the complement system, which is considered an important host defense mechanism against Aspergillus fumigatus, one of the most ubiquitous opportunistic human fungal pathogens. Previously, it has been shown that the alkaline protease Alp1p secreted from A. fumigatus mycelia degrades the complement components C3, C4, and C5. However, it remains unclear how the fungal spores (i.e. conidia) defend themselves against the activities of the complement system immediately after inhalation into the lung. Here, we show that A. fumigatus conidia contain a metalloprotease Mep1p, which is released upon conidial contact with collagen and inactivates all three complement pathways. In particular, Mep1p efficiently inactivated the major complement components C3, C4, and C5 and their activation products (C3a, C4a, and C5a) as well as the pattern-recognition molecules MBL and ficolin-1, either by directly cleaving them or by cleaving them to a form that is further broken down by other proteases of the complement system. Moreover, incubation of Mep1p with human serum significantly inhibited the complement hemolytic activity and conidial opsonization by C3b and their subsequent phagocytosis by macrophages. Together, these results indicate that Mep1p associated with and released from A. fumigatus conidia likely facilitates early immune evasion by disarming the complement defense in the human host.

Preventing loss of mechanosensation by the nuclear membranes of alveolar cells reduces lung injury in mice during mechanical ventilation.

The nuclear membrane acts as a mechanosensor that drives cellular responses following changes in the extracellular environment. Mechanically ventilated lungs are exposed to an abnormally high mechanical load that may result in clinically relevant alveolar damage. We report that mechanical ventilation in mice increased the expression of Lamin-A, a major determinant of nuclear membrane stiffness, in alveolar epithelial cells. Lamin-A expression increased and nuclear membrane compliance decreased in human bronchial epithelial cells after a mechanical stretch stimulus and in a murine model of lung injury after positive-pressure ventilation. Reducing Lamin-A maturation by depletion of the protease-encoding gene Zmpste24 preserved alveolar nuclear membrane compliance after mechanical ventilation in mice. Ventilator-induced proapoptotic gene expression changes and lung injury were reduced in mice lacking Zmpste24 compared to wild-type control animals. Similarly, treatment with the human immunodeficiency virus protease inhibitors lopinavir and ritonavir reduced the accumulation of Lamin-A at nuclear membranes and preserved nuclear membrane compliance after mechanical ventilation, mimicking the protective phenotype of Zmpste24-/- animals. These results show that the pathophysiological response to lung mechanical stretch is sensed by the nuclear membranes of lung alveolar cells, and suggest that protease inhibitors might be effective in preventing ventilator-induced lung injury.

Abnormal nuclear morphology is independent of longevity in a zmpste24-deficient fish model of Hutchinson-Gilford progeria syndrome (HGPS).

Lamin is an intermediate protein underlying the nuclear envelope and it plays a key role in maintaining the integrity of the nucleus. A defect in the processing of its precursor by a metalloprotease, ZMPSTE24, results in the accumulation of farnesylated prelamin in the nucleus and causes various diseases, including Hutchinson-Gilford progeria syndrome (HGPS). However, the role of lamin processing is unclear in fish species. Here, we generated zmpste24-deficient medaka and evaluated their phenotype. Unlike humans and mice, homozygous mutants did not show growth defects or lifespan shortening, despite lamin precursor accumulation. Gonadosomatic indices, blood glucose levels, and regenerative capacity of fins were similar in 1-year-old mutants and their wild-type (WT) siblings. Histological examination showed that the muscles, subcutaneous fat tissues, and gonads were normal in the mutants at the age of 1 year. However, the mutants showed hypersensitivity to X-ray irradiation, although p53target genes, p21 and mdm2, were induced 6 h after irradiation. Immunostaining of primary cultured cells from caudal fins and visualization of nuclei using H2B-GFP fusion proteins revealed an abnormal nuclear shape in the mutants both in vitro and in vivo. The telomere lengths were significantly shorter in the mutants compared to WT. Taken together, these results suggest that zmpste24-deficient medaka phenocopied HGPS only partially and that abnormal nuclear morphology and lifespan shortening are two independent events in vertebrates.

Loss of the Drosophila m-AAA mitochondrial protease paraplegin results in mitochondrial dysfunction, shortened lifespan, and neuronal and muscular degeneration.

The progressive accumulation of dysfunctional mitochondria is implicated in aging and in common diseases of the elderly. To oppose this occurrence, organisms employ a variety of strategies, including the selective degradation of oxidatively damaged and misfolded mitochondrial proteins. Genetic studies in yeast indicate that the ATPase Associated with diverse cellular Activities (AAA+) family of mitochondrial proteases account for a substantial fraction of this protein degradation, but their metazoan counterparts have been little studied, despite the fact that mutations in the genes encoding these proteases cause a variety of human diseases. To begin to explore the biological roles of the metazoan mitochondrial AAA+ protease family, we have created a CRISPR/Cas9 allele of the Drosophila homolog of SPG7, which encodes an inner membrane-localized AAA+ protease known as paraplegin. Drosophila SPG7 mutants exhibited shortened lifespan, progressive locomotor defects, sensitivity to chemical and environmental stress, and muscular and neuronal degeneration. Ultrastructural examination of photoreceptor neurons indicated that the neurodegenerative phenotype of SPG7 mutants initiates at the synaptic terminal. A variety of mitochondrial defects accompanied the degenerative phenotypes of SPG7 mutants, including altered axonal transport of mitochondria, accumulation of electron-dense material in the matrix of flight muscle mitochondria, reduced activities of respiratory chain complexes I and II, and severely swollen and dysmorphic mitochondria in the synaptic terminals of photoreceptors. Drosophila SPG7 mutants recapitulate key features of human diseases caused by mutations in SPG7, and thus provide a foundation for the identification of Drosophila paraplegin substrates and strategies that could be used to ameliorate the symptoms of these diseases.

Phenotypic heterogeneity of ZMPSTE24 deficiency.

A 4-year-old girl was referred to the Undiagnosed Diseases Network with a history of short stature, thin and translucent skin, macrocephaly, small hands, and camptodactyly. She had been diagnosed with possible Hallerman-Streiff syndrome. Her evaluation showed that she was mosaic for uniparental isodisomy of chromosome 1, which harbored a pathogenic c.1077dupT variant in ZMPSTE24 which predicts p.(Leu362fsX18). ZMPSTE24 is a zinc metalloproteinase that is involved in processing farnesylated proteins and pathogenic ZMPSTE24 variants cause accumulation of abnormal farnesylated forms of prelamin A. This, in turn, causes a spectrum of disease severity which is based on enzyme activity. The current patient has an intermediate form, which is a genocopy of severe Progeria.

miR­342­5p promotes Zmpste24­deficient mouse embryonic fibroblasts proliferation by suppressing GAS2.

Cellular senescence is an irreversible growth arrest of cells that maintain their metabolic activities. Premature senescence can be induced by different stress factors and occurs in mouse embryonic fibroblasts (MEFs) derived from Zmpste24 metalloproteinase­deficient mice, a progeria mouse model of Hutchinson­Gilford Progeria Syndrome. Previous studies have shown that miR­342­5p, an intronic microRNA (miRNA/miR) reportedly involved in ageing associated diseases, is downregulated in Zmpste24­/­ MEFs. However, whether miR­342­5p is associated with the premature senescence phenotype of Zmpste24­/­ MEFs remains unclear. Thus, the present study investigated the effects of miR­342­5p on cellular senescence and cell proliferation in Zmpste24­/­ MEFs. The results showed that miR­342­5p overexpression ameliorated the cellular senescence phenotype to a certain extent, promoted cell proliferation and increased the G2+M cell cycle phase in Zmpste24­/­ MEFs. Nonetheless, it was difficult to observe the opposite cell phenotypes in wild­type (WT) MEFs transfected with the miR­342­5p inhibitor. Growth­arrest­specific 2 (GAS2) was identified as a target gene of miR­342­5p in Zmpste24­/­ MEFs. In addition, miR­342­5p was identified to be downregulated in WT MEFs during replicative senescence, while Gas2 was upregulated. Taken together, these findings suggest that downregulated miR­342­5p is involved in regulating cell proliferation and cell cycles in Zmpste24­/­ MEFs by suppressing GAS2 in vitro.

Mutations in KEOPS-complex genes cause nephrotic syndrome with primary microcephaly.

Galloway-Mowat syndrome (GAMOS) is an autosomal-recessive disease characterized by the combination of early-onset nephrotic syndrome (SRNS) and microcephaly with brain anomalies. Here we identified recessive mutations in OSGEP, TP53RK, TPRKB, and LAGE3, genes encoding the four subunits of the KEOPS complex, in 37 individuals from 32 families with GAMOS. CRISPR-Cas9 knockout in zebrafish and mice recapitulated the human phenotype of primary microcephaly and resulted in early lethality. Knockdown of OSGEP, TP53RK, or TPRKB inhibited cell proliferation, which human mutations did not rescue. Furthermore, knockdown of these genes impaired protein translation, caused endoplasmic reticulum stress, activated DNA-damage-response signaling, and ultimately induced apoptosis. Knockdown of OSGEP or TP53RK induced defects in the actin cytoskeleton and decreased the migration rate of human podocytes, an established intermediate phenotype of SRNS. We thus identified four new monogenic causes of GAMOS, describe a link between KEOPS function and human disease, and delineate potential pathogenic mechanisms.

Damage-induced neuronal endopeptidase (DINE) enhances axonal regeneration potential of retinal ganglion cells after optic nerve injury.

Damage-induced neuronal endopeptidase (DINE)/endothelin-converting enzyme-like 1 (ECEL1) is a membrane-bound metalloprotease that we identified as a nerve regeneration-associated molecule. The expression of DINE is upregulated in response to nerve injury in both the peripheral and central nervous systems, while its transcription is regulated by the activating transcription factor 3 (ATF3), a potent hub-transcription factor for nerve regeneration. Despite its unique hallmark of injury-induced upregulation, the physiological relevance of DINE in injured neurons has been unclear. In this study, we have demonstrated that the expression of DINE is upregulated in injured retinal ganglion cells (RGCs) in a coordinated manner with that of ATF3 after optic nerve injury, whereas DINE and ATF3 are not observed in any normal retinal cells. Recently, we have generated a mature DINE-deficient (KOTg) mouse, in which exogenous DINE is overexpressed specifically in embryonic motor neurons to avoid aberrant arborization of motor nerves and lethality after birth that occurs in the conventional DINE KO mouse. The DINE KOTg mice did not show any difference in retinal structure and the projection to brain from that of wild-type (wild type) mice under normal conditions. However, injured RGCs of DINE KOTg mice failed to regenerate even after the zymosan treatment, which is a well-known regeneration-promoting reagent. Furthermore, a DINE KOTg mouse crossed with a Atf3:BAC Tg mouse, in which green fluorescent protein (GFP) is visualized specifically in injured RGCs and optic nerves, has verified that DINE deficiency leads to regeneration failure. These findings suggest that injury-induced DINE is a crucial endopeptidase for injured RGCs to promote axonal regeneration after optic nerve injury. Thus, a DINE-mediated proteolytic mechanism would provide us with a new therapeutic strategy for nerve regeneration.