The cerebral cavernous malformation 3 gene is necessary for senescence induction

Deficiency of Pdcd10 causes urothelium hypertrophy and vesicle trafficking defects in ureter

The scaffolding protein programmed cell death protein 10 (Pdcd10) has been demonstrated to play a critical role in renal epithelial cell homeostasis and function by maintaining appropriate water reabsorption in collecting ducts. Both ureter and kidney collecting duct systems are derived from the ureter bud during development. Here, we report that cadherin-16 (Cdh16)-cre drives gene recombination with high specificity in the ureter, but not the bladder, urothelium. The consequences of Pdcd10 deletion on the stratified ureter urothelium were investigated using an integrated approach including messenger RNA (mRNA) expression analysis, immunocytochemistry, and high-resolution confocal and electron microscopy. Loss of Pdcd10 in the ureter urothelium resulted in increased expression of uroplakins (Upks) and keratins (Krts), as well as hypertrophy of the ureter urothelium with an associated increase in the number of proliferation marker protein Ki-67 (Ki67)-expressing cells specifically within the basal urothelium layer. Ultrastructural analysis documented significant modification of the intracellular membrane system, including intracellular vesicle genesis and transport along the basal- to umbrella-cell-layer axis. Additionally, Pdcd10 loss resulted in swelling of Golgi compartments, disruption of mitochondrial cristae structure, and increased lysosomal fusion. Lack of Pdcd10 also resulted in decreased fusiform vesicle formation in umbrella cells, increased secretion of exosome vesicles, and alteration in microvillar structure on apical membranes. Our findings indicate that Pdcd10 expression and its influence on homeostasis is associated with modulation of endomembrane trafficking and organelle biogenesis in the ureter urothelium.

The Dual Role of PDCD10 in Cancers: A Promising Therapeutic Target

Programmed cell death 10 (PDCD10) was initially considered as a protein associated with apoptosis. However, recent studies showed that PDCD10 is actually an adaptor protein. By interacting with multiple molecules, PDCD10 participates in various physiological processes, such as cell survival, migration, cell differentiation, vesicle trafficking, cellular senescence, neurovascular development, and gonadogenesis. Moreover, over the past few decades, accumulating evidence has demonstrated that the aberrant expression or mutation of PDCD10 is extremely common in various pathological processes, especially in cancers. The dysfunction of PDCD10 has been strongly implicated in oncogenesis and tumor progression. However, the updated data seem to indicate that PDCD10 has a dual role (either pro- or anti-tumor effects) in various cancer types, depending on cell/tissue specificity with different cellular interactors. In this review, we aimed to summarize the knowledge of the dual role of PDCD10 in cancers with a special focus on its cellular function and potential molecular mechanism. With these efforts, we hoped to provide new insight into the future development and application of PDCD10 as a clinical therapeutic target in cancers.

Autophagy at the interface of endothelial cell homeostasis and vascular disease

Autophagy is an essential intracellular process for cellular quality control. It enables cell homeostasis through the selective degradation of harmful protein aggregates and damaged organelles. Autophagy is essential for recycling nutrients, generating energy to maintain cell viability in most tissues and during adverse conditions such as hypoxia/ischaemia. The progressive understanding of the mechanisms modulating autophagy in the vasculature has recently led numerous studies to link intact autophagic responses with endothelial cell (EC) homeostasis and function. Preserved autophagic flux within the ECs has an essential role in maintaining their physiological characteristics, whereas defective autophagy can promote endothelial pro-inflammatory and atherogenic phenotype. However, we still lack a good knowledge of the complete molecular repertoire controlling various aspects of endothelial autophagy and how this is associated with vascular diseases. Here, we provide an overview of the current state of the art of autophagy in ECs. We review the discoveries that have so far defined autophagy as an essential mechanism in vascular biology and analyse how autophagy influences ECs behaviour in vascular disease. Finally, we emphasise opportunities for compounds to regulate autophagy in ECs and discuss the challenges of exploiting them to resolve vascular disease.

GCKIII (Germinal Center Kinase III) Kinases STK24 and STK25 (Serine/Threonine Kinase 24 and 25) Inhibit Cavernoma Development

BACKGROUND

Cavernous cerebral malformations can arise because of mutations in the CCM1, CCM2, or CCM3 genes, and lack of Cdc42 has also been reported to induce these malformations in mice. However, the role of the CCM3 (cerebral cavernous malformation 3)-associated kinases in cavernoma development is not known, and we, therefore, have investigated their role in the process.

METHODS

We used a combination of an in vivo approach, using mice genetically modified to be deficient in the CCM3-associated kinases STK24 and STK25 (serine/threonine kinases 24 and 25), and the in vitro model of human endothelial cells in which expression of STK24 and STK25 was inhibited by RNA interference.

RESULTS

Mice deficient for both Stk24 and Stk25, but not for either of them individually, developed aggressive vascular lesions with the characteristics of cavernomas at an early age. Stk25 deficiency also gave rise to vascular anomalies in the context of Stk24 heterozygosity. Human endothelial cells deficient for both kinases phenocopied several of the consequences of CCM3 loss, and single STK25 deficiency also induced KLF2 expression, Golgi dispersion, altered distribution of β-catenin, and appearance of stress fibers.

CONCLUSIONS

The CCM3-associated kinases STK24 and STK25 play a major role in the inhibition of cavernoma development.

The multifaceted PDCD10/CCM3 gene

The programmed cell death 10 (PDCD10) gene was originally identified as an apoptosis-related gene, although it is now usually known as CCM3, as the third causative gene of cerebral cavernous malformation (CCM). CCM is a neurovascular disease that is characterized by vascular malformations and is associated with headaches, seizures, focal neurological deficits, and cerebral hemorrhage. The PDCD10/CCM3 protein has multiple subcellular localizations and interacts with several multi-protein complexes and signaling pathways. Thus PDCD10/CCM3 governs many cellular functions, which include cell-to-cell junctions and cytoskeleton organization, cell proliferation and apoptosis, and exocytosis and angiogenesis. Given its central role in the maintenance of homeostasis of the cell, dysregulation of PDCD10/CCM3 can result in a wide range of altered cell functions. This can lead to severe diseases, including CCM, cognitive disability, and several types of cancers. Here, we review the multifaceted roles of PDCD10/CCM3 in physiology and pathology, with a focus on its functions beyond CCM.

Cellular senescence at the crossroads of inflammation and Alzheimer's disease

Aging is a key risk factor for Alzheimer's disease (AD), but the reasons for this association are not well understood. Senescent cells accumulate in aged tissues and have been shown to play causal roles in age-related pathologies through their proinflammatory secretome. The question arises whether senescence-induced inflammation might contribute to AD and bridge the gap between aging and AD. Here, we highlight the role of cellular senescence as a driver of the aging phenotype, and discuss the current evidence that connects senescence with AD and neurodegeneration.

CCM2-deficient endothelial cells undergo a ROCK-dependent reprogramming into senescence-associated secretory phenotype

Cerebral cavernous malformation (CCM) is a cerebrovascular disease in which stacks of dilated haemorrhagic capillaries form focally in the brain. Whether and how defective mechanotransduction, cellular mosaicism and inflammation interplay to sustain the progression of CCM disease is unknown. Here, we reveal that CCM1- and CCM2-silenced endothelial cells expanded in vitro enter into senescence-associated secretory phenotype (SASP) that they use to invade the extracellular matrix and attract surrounding wild-type endothelial and immune cells. Further, we demonstrate that this SASP is driven by the cytoskeletal, molecular and transcriptomic disorders provoked by ROCK dysfunctions. By this, we propose that CCM2 and ROCK could be parts of a scaffold controlling senescence, bringing new insights into the emerging field of the control of ageing by cellular mechanics. These in vitro findings reconcile the known dysregulated traits of CCM2-deficient endothelial cells into a unique endothelial fate. Based on these in vitro results, we propose that a SASP could link the increased ROCK-dependent cell contractility in CCM2-deficient endothelial cells with microenvironment remodelling and long-range chemo-attraction of endothelial and immune cells.

Endothelial cell senescence: A machine learning-based meta-analysis of transcriptomic studies

Numerous systemic vascular dysfunction that leads to age-related diseases is highly associated with endothelial cell (EC) senescence; thus, identifying consensus features of EC senescence is crucial in understanding the mechanisms and identifying potential therapeutic targets. Here, by utilizing a total of 8 screened studies from different origins of ECs, we have successfully obtained common features in both gene and pathway level via sophisticated machine learning algorithms. A total of 400 differentially expressed genes (DEGs) were newly discovered with meta-analysis when compared to the usage of individual studies. The generated parsimonious model established 36 genes and 57 pathways features with non-zero coefficient, suggesting remarkable association of phosphoglycerate dehydrogenase and serine biosynthesis pathway with endothelial cellular senescence. For the cross-validation process to measure model performance of 36 deduced features, leave-one-study-out cross-validation (LOSOCV) was employed, resulting in an overall area under the receiver operating characteristic (AUROC) of 0.983 (95 % CI, 0.952, 1.000) showing excellent discriminative performance. Moreover, pathway-level analysis was performed by Pathifier algorithm, obtaining a total of 698 pathway deregulation scores from the 10,416 merged genes. In this process, high dimensional data was eventually narrowed down to 57 core pathways with AUROC value of 0.982 (95 % CI, 0.945, 1.000). The robust model with high performance underscores the merit of utilizing sophisticated meta-analysis in finding consensus features of endothelial cell senescence, which may lead to the development of therapeutic targets and advanced understanding of vascular dysfunction pathogenesis with further elucidation.

High Levels of Receptor Tyrosine Kinases in CCM3-Deficient Cells Increase Their Susceptibility to Tyrosine Kinase Inhibition

Cerebral cavernous malformations (CCMs) are vascular malformations that can be the result of the deficiency of one of the CCM genes. Their only present treatment is surgical removal, which is not always possible, and an alternative pharmacological strategy to eliminate them is actively sought. We have studied the effect of the lack of one of the CCM genes, CCM3, in endothelial and non-endothelial cells. By comparing protein expression in control and CCM3-silenced cells, we found that the levels of the Epidermal Growth Factor Receptor (EGFR) are higher in CCM3-deficient cells, which adds to the known upregulation of Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) in these cells. Whereas VEGFR2 is upregulated at the mRNA level, EGFR has a prolonged half-life. Inhibition of EGFR family members in CCM3-deficient cells does not revert the known cellular effects of lack of CCM genes, but it induces significantly more apoptosis in CCM3-deficient cells than in control cells. We propose that the susceptibility to tyrosine kinase inhibitors of CCM3-deficient cells can be harnessed to kill the abnormal cells of these lesions and thus treat CCMs pharmacologically.

Detection of p62/SQSTM1 Aggregates in Cellular Models of CCM Disease by Immunofluorescence

Cerebral cavernous malformations (CCM) is a familial or sporadic rare disorder that is characterized by capillary vascular lesions with a mulberry-like appearance on MRI scans. Three distinct genes have been associated to CCM disease, known as CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10. Loss-of-functions mutations on these genes lead to deregulation in multiple signaling pathways, thereby resulting in disturbed vessel organization and function. Insufficient autophagy has been observed upon downregulation of all three CCM genes, both in cells and human patient tissues, revealed as aberrant accumulation of the autophagy receptor p62/SQSTM1. The autophagic process is conceived as an adaptive response to stress and is essential for the maintenance of cellular homeostasis. The aim of this review is to briefly summarize the current knowledge on the role of autophagy in CCM disease and to furnish a detailed protocol for detecting and measuring p62/SQSTM1 cytoplasmic aggregates through immunofluorescence technique.

CCM3 and cerebral cavernous malformation disease

Cerebral cavernous malformations (CCMs) are vascular lesions characterised by enlarged and irregular structure of small blood vessels in the brain, which can result in increased risk of stroke, focal neurological defects and seizures. Three different genes, CCM1/Krev/Rap1 Interacting Trapped 1, CCM2/MGC4607 and CCM3/PDCD10, are associated with the CCMs’ progression, and mutations in one of three CCM genes cause CCM disease. These three CCM proteins have similar function in maintaining the normal structure of small blood vessels. However, CCM3 mutation results in a more severe form of the disease which may suggest that CCM3 has unique biological function in the vasculature. The current review focuses on the signalling pathways mediated by CCM3 in regulating endothelial cell junction, proliferation, migration and permeability. These findings may offer potential therapeutic strategies for the treatment of CCMs.

Methylome of human senescent hematopoietic progenitors

Senescence, a state of permanent cell cycle arrest, can be induced by DNA damage. This process, which was initially described in fibroblasts, is now recognized to occur in stem cells. It has been well characterized in cell lines, but there is currently very limited data available on human senescence in vivo. We recently reported that the expression of transposable elements (TE), including endogenous retroviruses, was up-regulated along with inflammatory genes in human senescent hematopoietic stem and progenitor cells (HSPCs) in vivo. The mechanism of regulation of TE expression is not completely understood, but changes in DNA methylation and chromatin modifications are known to alter their expression. In order to elucidate the molecular mechanisms for TE up-regulation after senescence of HSPCs, we employed whole-genome bisulfite sequencing in paired senescent and active human HSPCs in vivo from healthy subjects. We found that the senescent HSPCs exhibited hypomethylated regions in the genome, which were enriched for TEs. This is the first report characterizing the methylome of senescent human HSPCs.

Biallelic CCM3 mutations cause a clonogenic survival advantage and endothelial cell stiffening

CCM3, originally described as PDCD10, regulates blood‐brain barrier integrity and vascular maturation in vivo. CCM3 loss‐of‐function variants predispose to cerebral cavernous malformations (CCM). Using CRISPR/Cas9 genome editing, we here present a model which mimics complete CCM3 inactivation in cavernous endothelial cells (ECs) of heterozygous mutation carriers. Notably, we established a viral‐ and plasmid‐free crRNA:tracrRNA:Cas9 ribonucleoprotein approach to introduce homozygous or compound heterozygous loss‐of‐function CCM3 variants into human ECs and studied the molecular and functional effects of long‐term CCM3 inactivation. Induction of apoptosis, sprouting, migration, network and spheroid formation were significantly impaired upon prolonged CCM3 deficiency. Real‐time deformability cytometry demonstrated that loss of CCM3 induces profound changes in cell morphology and mechanics: CCM3‐deficient ECs have an increased cell area and elastic modulus. Small RNA profiling disclosed that CCM3 modulates the expression of miRNAs that are associated with endothelial ageing. In conclusion, the use of CRISPR/Cas9 genome editing provides new insight into the consequences of long‐term CCM3 inactivation in human ECs and supports the hypothesis that clonal expansion of CCM3‐deficient dysfunctional ECs contributes to CCM formation.

Recent advances in cerebral cavernous malformation research

Cerebral cavernous malformations (CCM) are manifested by microvascular lesions characterized by leaky endothelial cells with minimal intervening parenchyma predominantly in the central nervous system predisposed to hemorrhagic stroke, resulting in focal neurological defects. Till date, three proteins are implicated in this condition: CCM1 (KRIT1), CCM2 (MGC4607), and CCM3 (PDCD10). These multi-domain proteins form a protein complex via CCM2 that function as a docking site for the CCM signaling complex, which modulates many signaling pathways. Defects in the formation of this signaling complex have been shown to affect a wide range of cellular processes including cell-cell contact stability, vascular angiogenesis, oxidative damage protection and multiple biogenic events. In this review we provide an update on recent advances in structure and function of these CCM proteins, especially focusing on the signaling cascades involved in CCM pathogenesis and the resultant CCM cellular phenotypes in the past decade.

Defective autophagy is a key feature of cerebral cavernous malformations

Cerebral cavernous malformation (CCM) is a major cerebrovascular disease affecting approximately 0.3-0.5% of the population and is characterized by enlarged and leaky capillaries that predispose to seizures, focal neurological deficits, and fatal intracerebral hemorrhages. Cerebral cavernous malformation is a genetic disease that may arise sporadically or be inherited as an autosomal dominant condition with incomplete penetrance and variable expressivity. Causative loss-of-function mutations have been identified in three genes, KRIT1 (CCM1), CCM2 (MGC4607), and PDCD10 (CCM3), which occur in both sporadic and familial forms. Autophagy is a bulk degradation process that maintains intracellular homeostasis and that plays essential quality control functions within the cell. Indeed, several studies have identified the association between dysregulated autophagy and different human diseases. Here, we show that the ablation of the KRIT1 gene strongly suppresses autophagy, leading to the aberrant accumulation of the autophagy adaptor p62/SQSTM1, defective quality control systems, and increased intracellular stress. KRIT1 loss-of-function activates the mTOR-ULK1 pathway, which is a master regulator of autophagy, and treatment with mTOR inhibitors rescues some of the mole-cular and cellular phenotypes associated with CCM. Insufficient autophagy is also evident in CCM2-silenced human endothelial cells and in both cells and tissues from an endothelial-specific CCM3-knockout mouse model, as well as in human CCM lesions. Furthermore, defective autophagy is highly correlated to endothelial-to-mesenchymal transition, a crucial event that contributes to CCM progression. Taken together, our data point to a key role for defective autophagy in CCM disease pathogenesis, thus providing a novel framework for the development of new pharmacological strategies to prevent or reverse adverse clinical outcomes of CCM lesions.

Loss of endothelial programmed cell death 10 activates glioblastoma cells and promotes tumor growth

BACKGROUND

Neo-angiogenesis is a hallmark of glioblastoma (GBM) and is sustained by autocrine and paracrine interactions between neoplastic and nonneoplastic cells. Programmed cell death 10 (PDCD10) is ubiquitously expressed in nearly all tissues and plays crucial roles in regulating angiogenesis and apoptosis. We recently discovered the absence of PDCD10 expression in the tumor vessels of GBM patients. This raised the hypothesis that loss of endothelial PDCD10 affected GBM cell phenotyping and tumor progression.

METHODS

Endothelial PDCD10 was silenced by siRNA and lentiviral shRNA. The tumor cell phenotype was studied in direct and indirect co-culture of endothelial cells (ECs) with U87 or LN229. Angiogenic protein array was performed in the media of PDCD10-silenced ECs. Tumor angiogenesis and tumor growth were investigated in a human GBM xenograft mouse model.

RESULTS

Endothelial silence of PDCD10 significantly stimulated tumor cell proliferation, migration, adhesion, and invasion and inhibited apoptosis in co-cultures. Stable knockdown of endothelial PDCD10 increased microvessel density and the formation of a functional vascular network, leading to a 4-fold larger tumor mass in mice. Intriguingly, endothelial deletion of PDCD10 increased (≥2-fold) the release of 20 of 55 tested proangiogenic factors including VEGF, which in turn activated Erk1/2 and Akt in GBM cells.

CONCLUSIONS

For the first time, we provide evidence that loss of endothelial PDCD10 activates GBM cells and promotes tumor growth, most likely via a paracrine mechanism. PDCD10 shows a tumor-suppressor-like function in the cross talk between ECs and tumor cells and is potentially implicated in GBM progression.