Polycystin-1, the PKD1 gene product, is in a complex containing E-cadherin and the catenins

Inverted apicobasal polarity in health and disease

Apicobasal epithelial polarity controls the functional properties of most organs. Thus, there has been extensive research on the molecular intricacies governing the establishment and maintenance of cell polarity. Whereas loss of apicobasal polarity is a well-documented phenomenon associated with multiple diseases, less is known regarding another type of apicobasal polarity alteration - the inversion of polarity. In this Review, we provide a unifying definition of inverted polarity and discuss multiple scenarios in mammalian systems and human health and disease in which apical and basolateral membrane domains are interchanged. This includes mammalian embryo implantation, monogenic diseases and dissemination of cancer cell clusters. For each example, the functional consequences of polarity inversion are assessed, revealing shared outcomes, including modifications in immune surveillance, altered drug sensitivity and changes in adhesions to neighboring cells. Finally, we highlight the molecular alterations associated with inverted apicobasal polarity and provide a molecular framework to connect these changes with the core cell polarity machinery and to explain roles of polarity inversion in health and disease. Based on the current state of the field, failure to respond to extracellular matrix (ECM) cues, increased cellular contractility and membrane trafficking defects are likely to account for most cases of inverted apicobasal polarity.

Autosomal Dominant Polycystic Kidney Disease: Extrarenal Involvement

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disorder, but kidneys are not the only organs involved in this systemic disorder. Individuals with the condition may display additional manifestations beyond the renal system, involving the liver, pancreas, and brain in the context of cystic manifestations, while involving the vascular system, gastrointestinal tract, bones, and cardiac valves in the context of non-cystic manifestations. Despite kidney involvement remaining the main feature of the disease, thanks to longer survival, early diagnosis, and better management of kidney-related problems, a new wave of complications must be faced by clinicians who treated patients with ADPKD. Involvement of the liver represents the most prevalent extrarenal manifestation and has growing importance in the symptom burden and quality of life. Vascular abnormalities are a key factor for patients' life expectancy and there is still debate whether to screen or not to screen all patients. Arterial hypertension is often the earliest onset symptom among ADPKD patients, leading to frequent cardiovascular complications. Although cardiac valvular abnormalities are a frequent complication, they rarely lead to relevant problems in the clinical history of polycystic patients. One of the newest relevant aspects concerns bone disorders that can exert a considerable influence on the clinical course of these patients. This review aims to provide the "state of the art" among the extrarenal manifestation of ADPKD.

The molecular structure and function of fibrocystin, the key gene product implicated in autosomal recessive polycystic kidney disease (ARPKD)

Autosomal recessive polycystic kidney disease is an early onset inherited hepatorenal disorder affecting around 1 in 20,000 births with no approved specific therapies. The disease is almost always caused by variations in the polycystic kidney and hepatic disease 1 gene, which encodes fibrocystin (FC), a very large, single-pass transmembrane glycoprotein found in primary cilia, urine and urinary exosomes. By comparison to proteins involved in autosomal dominant PKD, our structural and molecular understanding of FC has lagged far behind such that there are no published experimentally determined structures of any part of the protein. Bioinformatics analyses predict that the ectodomain contains a long chain of immunoglobulin-like plexin-transcription factor domains, a protective antigen 14 domain, a tandem G8-TMEM2 homology region and a sperm protein, enterokinase and agrin domain. Here we review current knowledge on the molecular function of the protein from a structural perspective.

Autosomal Dominant Polycystic Kidney Disease: Is There a Role for Autophagy?

Autosomal-Dominant Polycystic Kidney Disease (ADPKD) is a monogenic disorder initiated by mutations in either PKD1 or PKD2 genes, responsible for encoding polycystin 1 and polycystin 2, respectively. These proteins are primarily located within the primary cilia. The disease follows an inexorable progression, leading most patients to severe renal failure around the age of 50, and extra-renal complications are frequent. A cure for ADPKD remains elusive, but some measures can be employed to manage symptoms and slow cyst growth. Tolvaptan, a vasopressin V2 receptor antagonist, is the only drug that has been proven to attenuate ADPKD progression. Recently, autophagy, a cellular recycling system that facilitates the breakdown and reuse of aged or damaged cellular components, has emerged as a potential contributor to the pathogenesis of ADPKD. However, the precise role of autophagy in ADPKD remains a subject of investigation, displaying a potentially twofold impact. On the one hand, impaired autophagy may promote cyst formation by inducing apoptosis, while on the other hand, excessive autophagy may lead to fibrosis through epithelial to mesenchymal transition. Promising results of autophagy inducers have been observed in preclinical studies. Clinical trials are warranted to thoroughly assess the long-term safety and efficacy of a combination of autophagy inducers with metabolic and/or aquaferetic drugs. This research aims to shed light on the complex involvement of autophagy in ADPKD, explore the regulation of autophagy in disease progression, and highlight the potential of combination therapies as a promising avenue for future investigations.

Functions of the primary cilium in the kidney and its connection with renal diseases

The nonmotile primary cilium is a sensory structure found on most mammalian cell types that integrates multiple signaling pathways involved in tissue development and postnatal function. As such, mutations disrupting cilia activities cause a group of disorders referred to as ciliopathies. These disorders exhibit a wide spectrum of phenotypes impacting nearly every tissue. In the kidney, primary cilia dysfunction caused by mutations in polycystin 1 (Pkd1), polycystin 2 (Pkd2), or polycystic kidney and hepatic disease 1 (Pkhd1), result in polycystic kidney disease (PKD), a progressive disorder causing renal functional decline and end-stage renal disease. PKD affects nearly 1 in 1000 individuals and as there is no cure for PKD, patients frequently require dialysis or renal transplantation. Pkd1, Pkd2, and Pkhd1 encode membrane proteins that all localize in the cilium. Pkd1 and Pkd2 function as a nonselective cation channel complex while Pkhd1 protein function remains uncertain. Data indicate that the cilium may act as a mechanosensor to detect fluid movement through renal tubules. Other functions proposed for the cilium and PKD proteins in cyst development involve regulation of cell cycle and oriented division, regulation of renal inflammation and repair processes, maintenance of epithelial cell differentiation, and regulation of mitochondrial structure and metabolism. However, how loss of cilia or cilia function leads to cyst development remains elusive. Studies directed at understanding the roles of Pkd1, Pkd2, and Pkhd1 in the cilium and other locations within the cell will be important for developing therapeutic strategies to slow cyst progression.

The GPCR properties of polycystin-1- A new paradigm

Polycystin-1 (PC1) is an 11-transmembrane (TM) domain-containing protein encoded by the PKD1 gene, the most frequently mutated gene leading to autosomal dominant polycystic kidney disease (ADPKD). This large (> 462 kDal) protein has a complex posttranslational maturation process, with over five proteolytic cleavages having been described, and is found at multiple cellular locations. The initial description of the binding and activation of heterotrimeric Gαi/o by the juxtamembrane region of the PC1 cytosolic C-terminal tail (C-tail) more than 20 years ago opened the door to investigations, and controversies, into PC1's potential function as a novel G protein-coupled receptor (GPCR). Subsequent biochemical and cellular-based assays supported an ability of the PC1 C-tail to bind numerous members of the Gα protein family and to either inhibit or activate G protein-dependent pathways involved in the regulation of ion channel activity, transcription factor activation, and apoptosis. More recent work has demonstrated an essential role for PC1-mediated G protein regulation in preventing kidney cyst development; however, the mechanisms by which PC1 regulates G protein activity continue to be discovered. Similarities between PC1 and the adhesion class of 7-TM GPCRs, most notably a conserved GPCR proteolysis site (GPS) before the first TM domain, which undergoes autocatalyzed proteolytic cleavage, suggest potential mechanisms for PC1-mediated regulation of G protein signaling. This article reviews the evidence supporting GPCR-like functions of PC1 and their relevance to cystic disease, discusses the involvement of GPS cleavage and potential ligands in regulating PC1 GPCR function, and explores potential connections between PC1 GPCR-like activity and regulation of the channel properties of the polycystin receptor-channel complex.

PKD1 deficiency induces Bronchiectasis in a porcine ADPKD model

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a prevalent genetic disorder, mainly characterized by the development of renal cysts, as well as various extrarenal manifestations. Previous studies have shown that ADPKD is related to bronchiectasis, while its pathogenic mechanism is unclear. In previous studies, we have generated the PKD1^+/- pigs to simulate the progression of cyst formation and physiological alterations similar to those seen in ADPKD patients.

METHODS

Phenotypic changes to airway epithelial cell and mesenchymal cell in PKD1^+/- pigs were assessed by histological analysis. The molecular mechanisms driving these processes were investigated by using PKD1^+/- pig lungs, human mesenchymal cells, and generating PKD1 deficient human epithelial cells.

RESULTS

We identified bronchiectasis in PKD1^+/- pigs, which is consistent with the clinical symptoms in ADPKD patients. The deficiency of PKD1 suppressed E-cadherin expression in the airway epithelial barrier, which aggravated invasion and leaded to a perpetuated inflammatory response. During this process, extracellular matrix (ECM) components were altered, which contributed to airway smooth muscle cell phenotype switch from a contractile phenotype to a proliferative phenotype. The effects on smooth muscle cells resulted in airway remodeling and establishment of bronchiectasis.

CONCLUSION

To our knowledge, the PKD1^+/- pig provides the first model recapitulating the pathogenesis of bronchiectasis in ADPKD. The role of PKD1 in airway epithelial suggests a potential target for development of new strategies for the diagnosis and treatment of bronchiectasis.

Retarding Progression of Chronic Kidney Disease in Autosomal Dominant Polycystic Kidney Disease with Metformin and Other Therapies: An Update of New Insights

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent single-gene disorder leading to renal failure. Current therapies are aimed to treat renal and extrarenal complications of ADPKD, but improved knowledge of the pathophysiological mechanisms leading to the generation and growth of cysts has permitted the identification of new drug candidates for clinical trials. Among these, in this review, we will examine above all the role of metformin, hypothesized to be able to activate the AMP-activated protein kinase (AMPK) pathway and potentially modulate some mechanisms implicated in the onset and the growth of the cysts.

Polycystin-1 is required for insulin-like growth factor 1-induced cardiomyocyte hypertrophy

Cardiac hypertrophy is the result of responses to various physiological or pathological stimuli. Recently, we showed that polycystin-1 participates in cardiomyocyte hypertrophy elicited by pressure overload and mechanical stress. Interestingly, polycystin-1 knockdown does not affect phenylephrine-induced cardiomyocyte hypertrophy, suggesting that the effects of polycystin-1 are stimulus-dependent. In this study, we aimed to identify the role of polycystin-1 in insulin-like growth factor-1 (IGF-1) signaling in cardiomyocytes. Polycystin-1 knockdown completely blunted IGF-1-induced cardiomyocyte hypertrophy. We then investigated the molecular mechanism underlying this result. We found that polycystin-1 silencing impaired the activation of the IGF-1 receptor, Akt, and ERK1/2 elicited by IGF-1. Remarkably, IGF-1-induced IGF-1 receptor, Akt, and ERK1/2 phosphorylations were restored when protein tyrosine phosphatase 1B was inhibited, suggesting that polycystin-1 knockdown deregulates this phosphatase in cardiomyocytes. Moreover, protein tyrosine phosphatase 1B inhibition also restored IGF-1-dependent cardiomyocyte hypertrophy in polycystin-1-deficient cells. Our findings provide the first evidence that polycystin-1 regulates IGF-1-induced cardiomyocyte hypertrophy through a mechanism involving protein tyrosine phosphatase 1B.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

Aggressive advanced gastric cancer in a patient with autosomal dominant polycystic kidney disease

A 60-year-old man with autosomal dominant polycystic kidney disease presented with malaise, melena, and epigastric discomfort. Esophagogastroduodenoscopy revealed a massive elevated gastric cancer lesion involving the cardia. Histopathological evaluation of a biopsy specimen showed poorly differentiated adenocarcinoma. Fluorodeoxyglucose-positron emission tomography revealed significant fluorodeoxyglucose uptake in the stomach, liver, bones, and bone marrow. He was diagnosed with metastatic gastric cancer resistant to chemotherapy, and he developed bone marrow carcinomatosis and disseminated intravascular coagulation and died 8 weeks after disease onset. A statistically significant association is reported between autosomal dominant polycystic kidney disease and gastric cancer. Moreover, the specific clinical features observed in our patient could be attributed to the molecular disorders like PC-1 and mechanistic target of rapamycin that are known to occur in autosomal dominant polycystic kidney disease.

Role of the polycystins as mechanosensors of extracellular stiffness

Polycystin-1 (PC-1) is a transmembrane protein, encoded by the PKD1 gene, mutated in autosomal dominant polycystic kidney disease (ADPKD). This common genetic disorder, characterized by cyst formation in both kidneys, ultimately leading to renal failure, is still waiting for a definitive treatment. The overall function of PC-1 and the molecular mechanism responsible for cyst formation are slowly coming to light, but they are both still intensively studied. In particular, PC-1 has been proposed to act as a mechanosensor, although the precise signal that activates the mechanical properties of this protein has been long debated and questioned. In this review, we report studies and evidence of PC-1 function as a mechanosensor, starting from the peculiarity of its structure, through the long journey that progressively shed new light on the potential initiating events of cystogenesis, concluding with the description of PC-1 recently shown ability to sense the mechanical stimuli provided by the stiffness of the extracellular environment. These new findings have potentially important implications for the understanding of ADPKD pathophysiology and potentially for designing new therapies.NEW & NOTEWORTHY Polycystin-1 has recently emerged as a possible receptor able to sense extracellular stiffness and to negatively control the cellular actomyosin contraction machinery. Here, we revisit a large body of literature on autosomal dominant polycystic kidney disease providing a new possible mechanistic view on the topic.

Renal Manifestations of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is a genetic condition caused by a mutation in either the TSC1 or TSC2 gene. Disruption of either of these genes leads to impaired production of hamartin or tuberin proteins, leading to the manifestation of skin lesions, tumors, and seizures. TSC can manifest in multiple organ systems with the cutaneous and renal systems being the most commonly affected. These manifestations can secondarily lead to the development of hypertension, chronic kidney disease, and neurocognitive declines. The renal pathologies most commonly seen in TSC are angiomyolipoma, renal cysts, and less commonly, oncocytomas. In this review, we highlight the current understanding on the renal manifestations of TSC along with current diagnosis and treatment guidelines.

A cut above (and below): Protein cleavage in the regulation of polycystin trafficking and signaling

The polycystin-1 and 2 proteins, encoded by the genes mutated in Autosomal Dominant Polycystic Kidney Disease, are connected to a large number of biological pathways. While the nature of these connections and their relevance to the primary functions of the polycystin proteins have yet to be fully elucidated, it is clear that many of them are mediated by or depend upon cleavage of the polycystin-1 protein. Cleavage of polycystin-1 at its G protein coupled receptor proteolytic site is an obligate step in the protein's maturation and in aspects of its trafficking. This cleavage may also serve to prime polycystin-1 to play a role as a non-canonical G protein coupled receptor. Cleavage of the cytoplasmic polycystin-1C terminal tail releases fragments that are able to enter the nucleus and the mitochondria and to influence their activities. Understanding the nature of these cleavages, their regulation and their consequences is likely to provide valuable insights into both the physiological functions served by the polycystin proteins and the pathological consequences of their absence.

Molecular pathways involved in injury-repair and ADPKD progression

The major hallmark of Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the formation of many fluid-filled cysts in the kidneys, which ultimately impairs the normal renal structure and function, leading to end-stage renal disease (ESRD). A large body of evidence suggests that injury-repair mechanisms are part of ADPKD progression. Once cysts have been formed, proliferation and fluid secretion contribute to the cyst size increase, which eventually causes stress on the surrounding tissue resulting in local injury and fibrosis. In addition, renal injury can cause or accelerate cyst formation. In this review, we will describe the various mechanisms activated during renal injury and tissue repair and show how they largely overlap with the molecular mechanisms activated during PKD progression. In particular, we will discuss molecular mechanisms such as proliferation, inflammation, cell differentiation, cytokines and growth factors secretion, which are activated following the renal injury to allow the remodelling of the tissue and a proper organ repair. We will also underline how, in a context of PKD-related gene mutations, aberrant or chronic activation of these developmental pathways and repair/remodelling mechanisms results in exacerbation of the disease.

Polycystins as components of large multiprotein complexes of polycystin interactors

Naturally occurring mutations in two separate genes, PKD1 and PKD2, are responsible for the vast majority of all cases of autosomal dominant polycystic kidney disease (ADPKD), one of the most common genetic diseases affecting 1 in 1000 Americans. The hallmark of ADPKD is the development of epithelial cysts in the kidney, liver, and pancreas. PKD1 encodes a large plasma membrane protein (PKD1, PC1, or Polycystin-1) with a long extracellular domain and has been speculated to function as an atypical G protein coupled receptor. PKD2 encodes an ion channel of the Transient Receptor Potential superfamily (TRPP2, PKD2, PC2, or Polycystin-2). Despite the identification of these genes more than 20 years ago, the molecular function of their encoded proteins and the mechanism(s) by which mutations in PKD1 and PKD2 cause ADPKD remain elusive. Genetic, biochemical, and functional evidence suggests they form a multiprotein complex present in multiple locations in the cell, including the plasma membrane, endoplasmic reticulum, and the primary cilium. Over the years, numerous interacting proteins have been identified using directed and unbiased approaches, and shown to modulate function, cellular localization, and protein stability and turnover of Polycystins. Delineation of the molecular composition of the Polycystin complex can have a significant impact on understanding their cellular function in health and disease states and on the identification of more specific and effective therapeutic targets.

Adhesion GPCRs as a paradigm for understanding polycystin-1 G protein regulation

Polycystin-1, whose mutation is the most frequent cause of autosomal dominant polycystic kidney disease, is an extremely large and multi-faceted membrane protein whose primary or proximal cyst-preventing function remains undetermined. Accumulating evidence supports the idea that modulation of cellular signaling by heterotrimeric G proteins is a critical function of polycystin-1. The presence of a cis-autocatalyzed, G protein-coupled receptor (GPCR) proteolytic cleavage site, or GPS, in its extracellular N-terminal domain immediately preceding the first transmembrane domain is one of the notable conserved features of the polycystin-1-like protein family, and also of the family of cell adhesion GPCRs. Adhesion GPCRs are one of five families within the GPCR superfamily and are distinguished by a large N-terminal extracellular region consisting of multiple adhesion modules with a GPS-containing GAIN domain and bimodal functions in cell adhesion and signal transduction. Recent advances from studies of adhesion GPCRs provide a new paradigm for unraveling the mechanisms by which polycystin-1-associated G protein signaling contributes to the pathogenesis of polycystic kidney disease. This review highlights the structural and functional features shared by polycystin-1 and the adhesion GPCRs and discusses the implications of such similarities for our further understanding of the functions of this complicated protein.

The master regulators Myc and p53 cellular signaling and functions in polycystic kidney disease

The transcription factors Myc and p53 associated with oncogenesis play determinant roles in a human genetic disorder, autosomal dominant polycystic kidney disease (ADPKD), that was coined early in ADPKD etiology a «neoplasia in disguise ». These factors are interdependent master cell regulators of major biological processes including proliferation, apoptosis, cell growth, metabolism, inflammation, fibrosis and differentiation that are all modulated in ADPKD. Myc and p53 proteins evolved to respond and carry out overlapping functions via opposing mechanisms of action. Studies in human ADPKD kidneys, caused by mutations in the PKD1 or PKD2 genes, reveal reduced p53 expression and high expression of Myc in the cystic tubular epithelium. Myc and p53 via direct interaction act respectively, as transcriptional activator and repressor of PKD1 gene expression, consistent with increased renal PKD1 levels in ADPKD. Mouse models generated by Pkd1 and Pkd2 gene dosage dysregulation reproduce renal cystogenesis with activation of Myc expression and numerous signaling pathways, strikingly similar to those determined in human ADPKD. In fact, upregulation of renal Myc expression is also detected in virtually all non-orthologous animal models of PKD. A definitive causal connection of Myc with cystogenesis was established by renal overexpression of Myc in transgenic mice that phenocopies human ADPKD. The network of activated signaling pathways in human and mouse cystogenesis individually or in combination can target Myc as a central node of PKD pathogenesis. One or many of the multiple functions of Myc upon activation can play a role in every phases of ADPKD development and lend credence to the notion of "Myc addiction" for cystogenesis. We propose that the residual p53 levels are conducive to an ADPKD biological program without cancerogenesis while a "p53 dependent annihilation" mechanism would be permissive to oncogenesis. Of major importance, Myc ablation in orthologous mouse models or direct inhibition in non-orthologous mouse model significantly delays cystogenesis consistent with pharmacologic or genetic inhibition of Myc upstream regulator or downstream targets in the mouse. Together, these studies on PKD proteins upon dysregulation not only converged on Myc as a focal point but also attribute to Myc upregulation a causal and « driver » role in pathogenesis. This review will present and discuss our current knowledge on Myc and p53, focused on PKD mouse models and ADPKD.

Set up of an in vitro model to study early host-parasite interactions between newly excysted juveniles of Fasciola hepatica and host intestinal cells using a quantitative proteomics approach

Fasciola hepatica is the causative agent of fasciolosis, a parasitic zoonosis of global distribution causing significant economic losses in animal production and a human public health problem in low-income countries. Hosts are infected by ingestion of aquatic plants carrying metacercariae. Once ingested, the juvenile parasites excyst in the small intestine and, after crossing it, they follow a complex migratory route that lead the parasites to their definitive location in the bile ducts. Despite being a critical event in the progression of the infection, the available data on the cross-talk relationships between the parasite and the host at an early stage of the infection are scarce. The objective of the present work is to characterize the proteomic changes occurring in both the parasite and the host, through the development of a novel in vitro model, to shed light on the molecular pathways of communication between the newly excysted juveniles (NEJ) from F. hepatica and the host's intestinal epithelium. For this, in vitro excystation of F. hepatica metacercariae was carried out and NEJ were obtained. Additionally, optimal conditions of growth and expansion of mouse primary small intestinal epithelial cells (MPSIEC) in culture were fine-tuned. Tegumentary and somatic parasite antigens (NEJ-Teg and NEJ-Som), as well as host cell protein lysate (MPSIEC-Lys) were obtained before and after 24 h co-culture of NEJ with MPSIEC. We used an isobaric tags for relative and absolute quantitation (iTRAQ)-based strategy to detect 191 and 62 up-regulated, and 112 and 57 down-regulated proteins in the NEJ-Teg and NEJ-Som extracts, respectively. Similarly, 87 up-regulated and 73 down-regulated proteins in the MPSIEC-Lys extract were identified. Taking into account the biological processes in which these proteins were involved, interesting mechanisms related to parasite development, invasion and evasion, as well as manipulation of the host intestinal epithelial cell adhesion, immunity and apoptosis pathways, among others, could be inferred, taking place at the host-parasite interface. The further understanding of these processes could constitute promising therapeutic targets in the future against fasciolosis.

Examining the Role of Polymorphisms in Exon 25 of the PKD1 Gene in the Pathogenesis of Autosomal Dominant Polycystic Kidney Disease in ranian Patients

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a highly prevalent life-threatening monogenic disorder with high morbidity and mortality. Roughly 1:400-1000 individuals are affected with this disease worldwide. The development of ADPKD is largely attributed to mutations in the polycystic kidney disease (PKD)1 and PKD2 genes. However, the pathogenicity of the different polymorphisms in PDK1 in the development of ADPKD remains unclear. The aim of this study was to further elucidate the role of the polymorphisms in exon 25 of the PDK1 gene in relation to the pathogenesis of ADPKD in Iranian patients.

METHODS

The genomic DNA of 36 Iranian patients with ADPKD was isolated using the standard salting out method. The PCR products were directly sequenced and analyzed.

RESULTS

The frequencies of CAG>GAG, ATG>GTG, GTC>GTA, and GTG>ATG polymorphisms in exon 25 of the PKD1 gene were 34 (94.44%), 33 (91.67%), 26 (72.22%), and 5 (13.89%), respectively. The most frequent polymorphism associated with ADPKD was the homozygous CAG→GAG which causes an amino acid change of Q[Gln] to E[Glu] at codon 3005.

CONCLUSION

Our data suggests that there is potentially a common polymorphism of PDK1 among the Iranian population with ADPKD. This may aid in the diagnosis and genetic screening of at-risk patients for ADPKD.

Autosomal dominant polycystic kidney disease: Disrupted pathways and potential therapeutic interventions

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic inherited renal cystic disease that occurs in different races worldwide. It is characterized by the development of a multitude of renal cysts, which leads to massive enlargement of the kidney and often to renal failure in adulthood. ADPKD is caused by a mutation in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Recent studies showed that cyst formation and growth result from deregulation of multiple cellular pathways like proliferation, apoptosis, metabolic processes, cell polarity, and immune defense. In ADPKD, intracellular cyclic adenosine monophosphate (cAMP) promotes cyst enlargement by stimulating cell proliferation and transepithelial fluid secretion. Several interventions affecting many of these defective signaling pathways have been effective in animal models and some are currently being tested in clinical trials. Moreover, the stem cell therapy can improve nephropathies and according to studies were done in this field, can be considered as a hopeful therapeutic approach in future for PKD. This study provides an in-depth review of the relevant molecular pathways associated with the pathogenesis of ADPKD and their implications in development of potential therapeutic strategies.

Bosutinib versus Placebo for Autosomal Dominant Polycystic Kidney Disease

Overactivation of Src has been linked to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). This phase 2, multisite study assessed the efficacy and safety of bosutinib, an oral dual Src/Bcr-Abl tyrosine kinase inhibitor, in patients with ADPKD. Patients with ADPKD, eGFR≥60 ml/min per 1.73 m2, and total kidney volume ≥750 ml were randomized 1:1:1 to bosutinib 200 mg/d, bosutinib 400 mg/d, or placebo for ≤24 months. The primary endpoint was annualized rate of kidney enlargement in patients treated for ≥2 weeks who had at least one postbaseline magnetic resonance imaging scan that was preceded by a 30-day washout (modified intent-to-treat population). Of 172 enrolled patients, 169 received at least one study dose. Per protocol amendment, doses for 24 patients who initially received bosutinib at 400 mg/d were later reduced to 200 mg/d. The annual rate of kidney enlargement was reduced by 66% for bosutinib 200 mg/d versus placebo (1.63% versus 4.74%, respectively; P=0.01) and by 82% for pooled bosutinib versus placebo (0.84% versus 4.74%, respectively; P<0.001). Over the treatment period, patients receiving placebo or bosutinib had similar annualized eGFR decline. Gastrointestinal and liver-related adverse events were the most frequent toxicities. In conclusion, compared with placebo, bosutinib at 200 mg/d reduced kidney growth in patients with ADPKD. The overall gastrointestinal and liver toxicity profile was consistent with the profile in prior studies of bosutinib; no new toxicities were identified. (ClinicalTrials.gov: NCT01233869).

Histological evaluation and E-cadherin and β-catenin expression in kidney of dogs submitted to renal ischemia and reperfusion after chlorpromazine administration

ABSTRACT Renal ischemia can be associated with some urological procedures, such as renovascular surgery or kidney transplantation, that are often followed by acute renal failure. The aim of this study was to verify the E-cadherin and β-catenin localization in canine kidney in different times of renal ischemia and reperfusion after chlorpromazine application. Twelve dogs were randomly distributed equally into two groups. GroupA with ischemia and reperfusion without chlorpromazine and groupB with ischemia and reperfusion treated by chlorpromazine. GroupB received intravenous chlorpromazine, 15 min before the artery obstruction, which lasted 1 hour. After this period, the clamps in the renal arteries were released and the organ remained in reperfusion for 2 hours. In each group, anti-E-cadherin and anti-β-catenin antibodies were made in six tissue samples from renal parenchyma. E-cadherin and β-catenin are differentially expressed in segments from cortex and medulla in dog’s kidneys and the use of chlorpromazine did not alter the expression of both proteins. Occlusion of the left renal artery in dogs causes morphological alterations mainly in proximal convoluted tubules, beginning 30min after the start of ischemia and being aggravated after two hours of reperfusion. These results reveal that chlorpromazine did not change kidneys’ histological aspect nor E-cadherin and β-catenin expression.

Polycystin and calcium signaling in cell death and survival

Mutations in polycystin-1 (PC1) and polycystin-2 (PC2) result in a commonly occurring genetic disorder, called Autosomal Dominant Polycystic Kidney Disease (ADPKD), that is characterized by the formation and development of kidney cysts. Epithelial cells with loss-of-function of PC1 or PC2 show higher rates of proliferation and apoptosis and reduced autophagy. PC1 is a large multifunctional transmembrane protein that serves as a sensor that is usually found in complex with PC2, a calcium (Ca²⁺)-permeable cation channel. In addition to decreased Ca²⁺ signaling, several other cell fate-related pathways are de-regulated in ADPKD, including cAMP, MAPK, Wnt, JAK-STAT, Hippo, Src, and mTOR. In this review we discuss how polycystins regulate cell death and survival, highlighting the complexity of molecular cascades that are involved in ADPKD.

On the Many Actions of Ouabain: Pro-Cystogenic Effects in Autosomal Dominant Polycystic Kidney Disease

Ouabain and other cardenolides are steroidal compounds originally discovered in plants. Cardenolides were first used as poisons, but after finding their beneficial cardiotonic effects, they were rapidly included in the medical pharmacopeia. The use of cardenolides to treat congestive heart failure remained empirical for centuries and only relatively recently, their mechanisms of action became better understood. A breakthrough came with the discovery that ouabain and other cardenolides exist as endogenous compounds that circulate in the bloodstream of mammals. This elevated these compounds to the category of hormones and opened new lines of investigation directed to further study their biological role. Another important discovery was the finding that the effect of ouabain was mediated not only by inhibition of the activity of the Na,K-ATPase (NKA), but by the unexpected role of NKA as a receptor and a signal transducer, which activates a complex cascade of intracellular second messengers in the cell. This broadened the interest for ouabain and showed that it exerts actions that go beyond its cardiotonic effect. It is now clear that ouabain regulates multiple cell functions, including cell proliferation and hypertrophy, apoptosis, cell adhesion, cell migration, and cell metabolism in a cell and tissue type specific manner. This review article focuses on the cardenolide ouabain and discusses its various in vitro and in vivo effects, its role as an endogenous compound, its mechanisms of action, and its potential use as a therapeutic agent; placing especial emphasis on our findings of ouabain as a pro-cystogenic agent in autosomal dominant polycystic kidney disease (ADPKD).

Ouabain promotes partial epithelial to mesenchymal transition (EMT) changes in human autosomal dominant polycystic kidney disease (ADPKD) cells

The hormone ouabain has been shown to enhance the cystic phenotype of autosomal dominant polycystic kidney disease (ADPKD). Among other characteristics, the ADPKD phenotype includes cell de-differentiation and epithelial to mesenchymal transition (EMT). Here, we determined whether physiological concentrations of ouabain induces EMT in human renal epithelial cells from patients with ADPKD. We found that ADPKD cells respond to ouabain with a decrease in expression of the epithelial marker E-cadherin and increase in the expression of the mesenchymal markers N-cadherin, α smooth muscle actin (αSMA) and collagen-I; and the tight junction protein occludin and claudin-1. Other adhesion molecules, such as ZO-1, β-catenin and vinculin were not significantly modified by ouabain. At the cellular level, ouabain stimulated ADPKD cell migration, reduced cell-cell interaction, and the ability of ADPKD cells to form aggregates. Moreover, ouabain increased the transepithelial electrical resistance of ADPKD cell monolayers, suggesting that the paracellular transport pathway was preserved in the cells. These effects of ouabain were not observed in normal human kidney (NHK) cells. Altogether these results show a novel role for ouabain in ADPKD, inducing changes that lead to a partial EMT phenotype in the cells. These effects further support the key role that ouabain has as a factor that promotes the cystic characteristics of ADPKD cells.

A holey pursuit: lumen formation in the developing kidney

The formation of polarized epithelial tubules is a hallmark of kidney development. One of the fundamental principles in tubulogenesis is that epithelia coordinate the polarity of individual cells with the surrounding cells and matrix. A central feature in this process is the segregation of membranes into spatially and functionally distinct apical and basolateral domains, and the generation of a luminal space at the apical surface. This review examines our current understanding of the cellular and molecular mechanisms that underlie the establishment of apical-basal polarity and lumen formation in developing renal epithelia, including the roles of cell-cell and cell-matrix interactions and polarity complexes. We highlight growing evidence from animal models, and correlate these findings with models of tubulogenesis from other organ systems, and from in vitro studies.

Polycystins and intercellular mechanotransduction: A precise dosage of polycystin 2 is necessary for alpha-actinin reinforcement of junctions upon mechanical stimulation

Polycystins 1 and 2, which are mutated in Autosomal Polycystic Kidney Disease, are involved in mechanotransduction through various mechanisms. In renal cells, polycystins not only have an important mechanotransductive role in primary cilia but are also present in intercellular contacts but their role there remains unclear. Here, we address the hypothesis that polycystins are involved in mechanotransduction via intercellular junctions, which would be expected to have consequences on tissue organization. We focused on the role of polycystin 2, which could be involved in mechanical organization at junctions either by its channel activity or by the direct recruitment of cytoskeleton components such as the F-actin cross-linker α-actinin. After mechanical stimulation of intercellular junctions in MDCK renal epithelial cells, α-actinin is rapidly recruited but this is inhibited upon overexpression of PC2 or the D509V mutant that lacks channel activity, and is also decreased upon PC2 silencing. This suggests that a precise dosage of PC2 is necessary for an adequate mechanosensitive α-actinin recruitment at junctions. At the multicellular level, a change in PC2 expression was associated with changes in velocity in confluent epithelia and during wound healing together with a loss of orientation. This study suggests that the mechanosensitive regulation of cytoskeleton by polycystins in intercellular contacts may be important in the context of ADPKD.

Gα12 is required for renal cystogenesis induced by Pkd1 inactivation

Mutation of PKD1, encoding the protein polycystin-1 (PC1), is the main cause of autosomal dominant polycystic kidney disease (ADPKD). The signaling pathways downstream of PC1 in ADPKD are still not fully understood. Here, we provide genetic evidence for the necessity of Gα12 (encoded by Gna12, hereafter Gα12) for renal cystogenesis induced by Pkd1 knockout. There was no phenotype in mice with deletion of Gα12 (Gα12^-/-). Polyinosine-polycytosine (pI:pC)-induced deletion of Pkd1 (Mx1Cre⁺Pkd1^f/fGα12^+/+) in 1-week-old mice resulted in multiple kidney cysts by 9 weeks, but the mice with double knockout of Pkd1 and Gα12 (Mx1Cre⁺Pkd1^f/fGα12^-/-) had no structural and functional abnormalities in the kidneys. These mice could survive more than one year without kidney abnormalities except multiple hepatic cysts in some mice, which indicates that the effect of Gα12 on cystogenesis is kidney specific. Furthermore, Pkd1 knockout promoted Gα12 activation, which subsequently decreased cell-matrix and cell-cell adhesion by affecting the function of focal adhesion and E-cadherin, respectively. Our results demonstrate that Gα12 is required for the development of kidney cysts induced by Pkd1 mutation in mouse ADPKD.

Proteomics of Urinary Vesicles Links Plakins and Complement to Polycystic Kidney Disease

Novel therapies in autosomal dominant polycystic kidney disease (ADPKD) signal the need for markers of disease progression or response to therapy. This study aimed to identify disease-associated proteins in urinary extracellular vesicles (uEVs), which include exosomes, in patients with ADPKD. We performed quantitative proteomics on uEVs from healthy controls and patients with ADPKD using a labeled approach and then used a label-free approach with uEVs of different subjects (healthy controls versus patients with ADPKD versus patients with non-ADPKD CKD). In both experiments, 30 proteins were consistently more abundant (by two-fold or greater) in ADPKD-uEVs than in healthy- and CKD-uEVs. Of these proteins, we selected periplakin, envoplakin, villin-1, and complement C3 and C9 for confirmation because they were also significantly overrepresented in pathway analysis and were previously implicated in ADPKD pathogenesis. Immunoblotting confirmed higher abundances of the selected proteins in uEVs from three independent groups of patients with ADPKD. Whereas uEVs of young patients with ADPKD and preserved kidney function already had higher levels of complement, only uEVs of patients with advanced stages of ADPKD had increased levels of villin-1, periplakin, and envoplakin. Furthermore, all five proteins correlated positively with total kidney volume. Analysis in kidney tissue from mice with kidney-specific, tamoxifen-inducible Pkd1 deletion demonstrated higher expression in more severe stages of the disease and correlation with kidney weight for each protein of interest. In summary, proteomic analysis of uEVs identified plakins and complement as disease-associated proteins in ADPKD. These proteins are new candidates for evaluation as biomarkers or targets for therapy in ADPKD.

Genetic Mechanisms of ADPKD

Autosomal dominant polycystic kidney disease is caused by mutation of PKD1 (polycystic kidney disease-1) or PKD2 (polycystic kidney disease-2). PKD1 and PKD2 encode PC1 (polycystin-1) and PC2 (polycystin-2), respectively. In addition, the mutation of cilia-associated proteins is also a recognized major factor of pathogenesis, since PC1 and PC2 are located in primary cilium. Abnormalities of PC1 or PC2 lead to aberrant signaling through downstream pathways, such as the negative growth regulation, G protein activation, and canonical and non-canonical Wnt pathways. According to the "second hit" model, an additional somatic mutation results in the expansion of cyst growth. In this chapter we discuss the genetic mechanisms and signaling pathways involved in ADPKD.

Polycystins and mechanotransduction: From physiology to disease

Polycystins are key mechanosensor proteins able to respond to mechanical forces of external or internal origin. They are widely expressed in primary cilium and plasma membrane of several cell types including kidney, vascular endothelial and smooth muscle cells, osteoblasts and cardiac myocytes modulating their physiology. Interaction of polycystins with diverse ion channels, cell-cell and cell-extracellular matrix junctional proteins implicates them in the regulation of cell structure, mechanical force transmission and mechanotransduction. Their intracellular localization in endoplasmic reticulum further regulates subcellular trafficking and calcium homeostasis, finely-tuning overall cellular mechanosensitivity. Aberrant expression or genetic alterations of polycystins lead to severe structural and mechanosensing abnormalities including cyst formation, deregulated flow sensing, aneurysms, defective bone development and cancer progression, highlighting their vital role in human physiology.

Polycystin-1 and Gα12 regulate the cleavage of E-cadherin in kidney epithelial cells

Interaction of polycystin-1 (PC1) and Gα12 is important for development of kidney cysts in autosomal dominant polycystic kidney disease (ADPKD). The integrity of cell polarity and cell-cell adhesions (mainly E-cadherin-mediated adherens junction) is altered in the renal epithelial cells of ADPKD. However, the key signaling pathway for this alteration is not fully understood. Madin-Darby canine kidney (MDCK) cells maintain the normal integrity of epithelial cell polarity and adherens junctions. Here, we found that deletion of Pkd1 increased activation of Gα12, which then promoted the cystogenesis of MDCK cells. The morphology of these cells was altered after the activation of Gα12. By using liquid chromatography-mass spectrometry, we found several proteins that could be related this change in the extracellular milieu. E-cadherin was one of the most abundant peptides after active Gα12 was induced. Gα12 activation or Pkd1 deletion increased the shedding of E-cadherin, which was mediated via increased ADAM10 activity. The increased shedding of E-cadherin was blocked by knockdown of ADAM10 or specific ADAM10 inhibitor GI254023X. Pkd1 deletion or Gα12 activation also changed the distribution of E-cadherin in kidney epithelial cells and caused β-catenin to shift from cell membrane to nucleus. Finally, ADAM10 inhibitor, GI254023X, blocked the cystogenesis induced by PC1 knockdown or Gα12 activation in renal epithelial cells. Our results demonstrate that the E-cadherin/β-catenin signaling pathway is regulated by PC1 and Gα12 via ADAM10. Specific inhibition of this pathway, especially ADAM10 activity, could be a novel therapeutic regimen for ADPKD.

Inactivation of integrin-β1 prevents the development of polycystic kidney disease after the loss of polycystin-1

Dysregulation of polycystin-1 (PC1) leads to autosomal dominant polycystic kidney disease (ADPKD), a disorder characterized by the formation of multiple bilateral renal cysts, the progressive accumulation of extracellular matrix (ECM), and the development of tubulointerstitial fibrosis. Correspondingly, cystic epithelia express higher levels of integrins (ECM receptors that control various cellular responses, such as cell proliferation, migration, and survival) that are characteristically altered in cystic cells. To determine whether the altered expression of ECM and integrins could establish a pathologic autostimulatory loop, we tested the role of integrin-β1 in vitro and on the cystic development of ADPKD in vivo. Compared with wild-type cells, PC1-depleted immortalized renal collecting duct cells had higher levels of integrin-β1 and fibronectin and displayed increased integrin-mediated signaling in the presence of Mn(2+). In mice, conditional inactivation of integrin-β1 in collecting ducts resulted in a dramatic inhibition of Pkd1-dependent cystogenesis with a concomitant suppression of fibrosis and preservation of normal renal function. Our data provide genetic evidence that a functional integrin-β1 is required for the early events leading to renal cystogenesis in ADPKD and suggest that the integrin signaling pathway may be an effective therapeutic target for slowing disease progression.

“Stop Ne(c)king around”: How interactomics contributes to functionally characterize Nek family kinases

Aside from Polo and Aurora, a third but less studied kinase family involved in mitosis regulation is the never in mitosis-gene A (NIMA)-related kinases (Neks). The founding member of this family is the sole member NIMA of Aspergillus nidulans, which is crucial for the initiation of mitosis in that organism. All 11 human Neks have been functionally assigned to one of the three core functions established for this family in mammals: (1) centrioles/mitosis; (2) primary ciliary function/ciliopathies; and (3) DNA damage response (DDR). Recent findings, especially on Nek 1 and 8, showed however, that several Neks participate in parallel in at least two of these contexts: primary ciliary function and DDR. In the core section of this in-depth review, we report the current detailed functional knowledge on each of the 11 Neks. In the discussion, we return to the cross-connections among Neks and point out how our and other groups’ functional and interactomics studies revealed that most Neks interact with protein partners associated with two if not all three of the functional contexts. We then raise the hypothesis that Neks may be the connecting regulatory elements that allow the cell to fine tune and synchronize the cellular events associated with these three core functions. The new and exciting findings on the Nek family open new perspectives and should allow the Neks to finally claim the attention they deserve in the field of kinases and cell cycle biology.

The primary cilium calcium channels and their role in flow sensing

The primary cilium has been the focus of intense research since it was discovered that mutations in ciliary/basal body localized proteins give rise to a multitude of disorders. While these studies have revealed the contribution of this sensory organelle to multiple signalling pathways, little is known about how it actually mediates downstream events and why its loss causes disease states. Ciliopathies are linked to defects in either structure or function of cilia and are often associated with kidney cysts. The ciliopathy, autosomal dominant polycystic kidney disease (ADPKD), is caused by mutations to the PKD1 or PKD2 gene. The PKD gene products localize to the primary cilium, where they have been proposed to form a mechanosensory complex, sensitive to flow. Since mouse knockout models of Pkd1 or Pkd2 develop structurally normal cilia, it has been hypothesized that the loss of polycystins may lead to an impairment of flow sensing. Today, technically challenging patch clamp recordings of the primary cilium have become available, and the genetic relationship between polycystins (TRPPs) and the primary cilium has recently been dissected in detail.

Polycystins and partners: proposed role in mechanosensitivity

Mutations of the two polycystins, PC1 and PC2, lead to polycystic kidney disease. Polycystins are able to form complexes with numerous families of proteins that have been suggested to participate in mechanical sensing. The proposed role of polycystins and their partners in the kidney primary cilium is to sense urine flow. A role for polycystins in mechanosensing has also been shown in other cell types such as vascular smooth muscle cells and cardiac myocytes. At the plasma membrane, polycystins interact with diverse ion channels of the TRP family and with stretch-activated channels (Piezos, TREKs). The actin cytoskeleton and its interacting proteins, such as filamin A, have been shown to be essential for these interactions. Numerous proteins involved in cell-cell and cell-extracellular matrix junctions interact with PC1 and/or PC2. These multimeric protein complexes are important for cell structure integrity, the transmission of force, as well as for mechanosensing and mechanotransduction. A group of polycystin partners are also involved in subcellular trafficking mechanisms. Finally, PC1 and especially PC2 interact with elements of the endoplasmic reticulum and are essential components of calcium homeostasis. In conclusion, we propose that both PC1 and PC2 act as conductors to tune the overall cellular mechanosensitivity.

The fate of the primary cilium during myofibroblast transition

Myofibroblasts, the culprit of organ fibrosis, can originate from mesenchymal and epithelial precursors through fibroblast-myofibroblast and epithelial-myofibroblast transition (EMyT). Because certain ciliopathies are associated with fibrogenesis, we sought to explore the fate and potential role of the primary cilium during myofibroblast formation. Here we show that myofibroblast transition from either precursor results in the loss of the primary cilium. During EMyT, initial cilium growth is followed by complete deciliation. Both EMyT and cilium loss require two-hit conditions: disassembly/absence of intercellular contacts and transforming growth factor-β1 (TGFβ) exposure. Loss of E-cadherin-dependent junctions induces cilium elongation, whereas both stimuli are needed for deciliation. Accordingly, in a scratch-wounded epithelium, TGFβ provokes cilium loss exclusively along the wound edge. Increased contractility, a key myofibroblast feature, is necessary and sufficient for deciliation, since constitutively active RhoA, Rac1, or myosin triggers, and down-regulation of myosin or myocardin-related transcription factor prevents, this process. Sustained myosin phosphorylation and consequent deciliation are mediated by a Smad3-, Rac1-, and reactive oxygen species-dependent process. Transitioned myofibroblasts exhibit impaired responsiveness to platelet-derived growth factor-AA and sonic hedgehog, two cilium-associated stimuli. Although the cilium is lost during EMyT, its initial presence contributes to the transition. Thus myofibroblasts represent a unique cilium-less entity with profoundly reprogrammed cilium-related signaling.

Smooth muscle cell transient receptor potential polycystin-2 (TRPP2) channels contribute to the myogenic response in cerebral arteries

Intravascular pressure-induced vasoconstriction is a smooth muscle cell-specific mechanism that controls systemic blood pressure and organ regional blood flow. Smooth muscle cell polycystin-1 and -2 (TRPP1 and -2) proteins modulate the myogenic response in mesenteric arteries, but involvement in other vascular beds is unclear. Here, we examined TRPP2 expression, cellular distribution, cation currents (ICat), and physiological functions in smooth muscle cells of rat and human cerebral arteries. We demonstrate that TRPP2 is the major TRPP isoform expressed in cerebral artery smooth muscle cells, with message levels higher than those of TRPP1. Arterial biotinylation and immunofluorescence indicated that TRPP2 is located primarily (∼88%) in the smooth muscle cell plasma membrane. RNA interference reduced TRPP2 expression by ∼55% compared to control, but did not alter levels of TRPP1, TRPC1, TRPC3, TRPC6, TRPM4, ANO1/TMEM16A, or voltage-dependent Ca(2+) (CaV1.2) channels, other ion channel proteins that modulate myogenic tone. Cell swelling induced by hyposmotic (250 osmol (l solution)(-1)) bath solution stimulated Gd(3+)-sensitive ICat in smooth muscle cells that were reduced by selective TRPP2 knockdown. TRPP2 knockdown did not alter myogenic tone at 20 mmHg but reduced tone between ∼28 and 39% over an intravascular pressure range between 40 and 100 mmHg. In contrast, TRPP2 knockdown did not alter depolarization-induced (60 mmol l K(+)) vasoconstriction. In summary, we show that TRPP2 is expressed in smooth muscle cells of resistance-size cerebral arteries, resides primarily in the plasma membrane, and contributes to the myogenic response. Data also suggest that TRPP2 differentially regulates the myogenic response in cerebral and mesenteric arteries.

Cell polarity and cystic kidney disease

Epithelial cell polarity is essential for organ development; aberrations in this process have been implicated in various diseases, including polycystic kidney disease. Establishment and maintenance of cell polarity is governed by a number of molecular processes and how these processes operate remains an interesting question. Conserved protein complexes guide both apical-basolateral polarity and planar cell polarity. In this review we discuss the recent findings that provide insights into polarity mechanisms and the intriguing crosstalk between apical-basolateral polarity and planar cell polarity, and their relationship to cystic kidney disease.

Primary cilia: the chemical antenna regulating human adipose-derived stem cell osteogenesis

Adipose-derived stem cells (ASC) are multipotent stem cells that show great potential as a cell source for osteogenic tissue replacements and it is critical to understand the underlying mechanisms of lineage specification. Here we explore the role of primary cilia in human ASC (hASC) differentiation. This study focuses on the chemosensitivity of the primary cilium and the action of its associated proteins: polycystin-1 (PC1), polycystin-2 (PC2) and intraflagellar transport protein-88 (IFT88), in hASC osteogenesis. To elucidate cilia-mediated mechanisms of hASC differentiation, siRNA knockdown of PC1, PC2 and IFT88 was performed to disrupt cilia-associated protein function. Immunostaining of the primary cilium structure indicated phenotypic-dependent changes in cilia morphology. hASC cultured in osteogenic differentiation media yielded cilia of a more elongated conformation than those cultured in expansion media, indicating cilia-sensitivity to the chemical environment and a relationship between the cilium structure and phenotypic determination. Abrogation of PC1, PC2 and IFT88 effected changes in both hASC proliferation and differentiation activity, as measured through proliferative activity, expression of osteogenic gene markers, calcium accretion and endogenous alkaline phosphatase activity. Results indicated that IFT88 may be an early mediator of the hASC differentiation process with its knockdown increasing hASC proliferation and decreasing Runx2, alkaline phosphatase and BMP-2 mRNA expression. PC1 and PC2 knockdown affected later osteogenic gene and end-product expression. PC1 knockdown resulted in downregulation of alkaline phosphatase and osteocalcin gene expression, diminished calcium accretion and reduced alkaline phosphatase enzymatic activity. Taken together our results indicate that the structure of the primary cilium is intimately associated with the process of hASC osteogenic differentiation and that its associated proteins are critical players in this process. Elucidating the dynamic role of the primary cilium and its associated proteins will help advance the application of hASC in generating autologous tissue engineered therapies in critical defect bone injuries.

The Roles of Primary cilia in Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited genetic disorder that results in progressive renal cyst formation with ultimate loss of renal function and other systemic disorders. These systemic disorders include abnormalities in cardiovascular, portal, pancreatic and gastrointestinal systems. ADPKD is considered to be among the ciliopathy diseases due to the association with abnormal primary cilia function. In order to understand the full course of primary cilia and its association with ADPKD, the structure, functions and role of primary cilia have been meticulously investigated. As a result, the focus on primary cilia has emerged to support the vital roles of primary cilia in ADPKD. The primary cilia have been shown to have not only a mechanosensory function but also a chemosensory function. Both structural and functional defects in primary cilia result in cystic kidney disease and vascular hypertension. Thus, the mechanosenory and chemosensory functions will be analyzed in regards to ADPKD.

VIP17/MAL expression modulates epithelial cyst formation and ciliogenesis

The polarized organization of epithelial cells is required for vectorial solute transport and may be altered in renal cystic diseases. Vesicle integral protein of 17 kDa (VIP17/MAL) is involved in apical vesicle transport. VIP17/MAL overexpression in vivo results in renal cystogenesis of unknown etiology. Renal cystogenesis can occur as a consequence of defects of the primary cilium. To explore the role of VIP17/MAL in renal cystogenesis and ciliogenesis, we examined the polarization and ciliary morphology of wild-type and VIP17/MAL overexpressing Madin-Darby canine kidney renal epithelial cells grown in two-dimensional (2D) and three-dimensional (3D) cyst culture. VIP17/MAL is apically localized when expressed in cells maintained in 2D and 3D culture. VIP17/MAL overexpressing cells produce more multilumen cysts compared with controls. While the distributions of basolateral markers are not affected, VIP17/MAL expression results in aberrant sorting of the apical marker gp135 to the primary cilium. VIP17/MAL overexpression is also associated with shortened or absent cilia. Immunofluorescence analysis performed on kidney sections from VIP17/MAL transgenic mice also demonstrates fewer and shortened cilia within dilated lumens (P < 0.01). These studies demonstrate that VIP17/MAL overexpression results in abnormal cilium and cyst development, in vitro and in vivo, suggesting that VIP17/MAL overexpressing mice may develop cysts secondary to a ciliary defect.

Polycystin-1 regulates the stability and ubiquitination of transcription factor Jade-1

Autosomal-dominant polycystic kidney disease (ADPKD) and von Hippel-Lindau (VHL) disease lead to large kidney cysts that share pathogenetic features. The polycystin-1 (PC1) and pVHL proteins may therefore participate in the same key signaling pathways. Jade-1 is a pro-apoptotic and growth suppressive ubiquitin ligase for beta-catenin and transcriptional coactivator associated with histone acetyltransferase activity that is stabilized by pVHL in a manner that correlates with risk of VHL renal disease. Thus, a relationship between Jade-1 and PC1 was sought. Full-length PC1 bound, stabilized and colocalized with Jade-1 and inhibited Jade-1 ubiquitination. In contrast, the cytoplasmic tail or the naturally occurring C-terminal fragment of PC1 (PC1-CTF) promoted Jade-1 ubiquitination and degradation, suggesting a dominant-negative mechanism. ADPKD-associated PC1 mutants failed to regulate Jade-1, indicating a potential disease link. Jade-1 ubiquitination was mediated by Siah-1, an E3 ligase that binds PC1. By controlling Jade-1 abundance, PC1 and the PC1-CTF differentially regulate Jade-1-mediated transcriptional activity. A key target of PC1, the cyclin-dependent kinase inhibitor p21, is also up-regulated by Jade-1. Through Jade-1, PC1 and PC1 cleaved forms may exert fine control of beta-catenin and canonical Wnt signaling, a critical pathway in cystic renal disease. Thus, Jade-1 is a transcription factor and ubiquitin ligase whose activity is regulated by PC1 in a manner that is physiologic and may correlate with disease. Jade-1 may be an important therapeutic target in renal cystogenesis.

The extracellular matrix and ciliary signaling

The primary cilium protrudes like an antenna from the cell surface, sensing mechanical and chemical cues provided in the cellular environment. In some tissue types, ciliary orientation to lumens allows response to fluid flow; in others, such as bone, ciliary protrusion into the extracellular matrix allows response to compression forces. The ciliary membrane contains receptors for Hedgehog, Wnt, Notch, and other potent growth factors, and in some instances also harbors integrin and cadherin family members, allowing receipt of a robust range of signals. A growing list of ciliopathies, arising from deficient formation or function of cilia, includes both developmental defects and chronic, progressive disorders such as polycystic kidney disease (PKD); changes in ciliary function have been proposed to support cancer progression. Recent findings have revealed extensive signaling dialog between cilia and extracellular matrix (ECM), with defects in cilia associated with fibrosis in multiple contexts. Further, a growing number of proteins have been determined to possess multiple roles in control of cilia and focal adhesion interactions with the ECM, further coordinating functionality. We summarize and discuss these recent findings.

Mechanoregulation of cytoskeletal dynamics by TRP channels

The ability of cells to respond to mechanical stimulation is crucial to a variety of biological processes, including cell migration, axonal outgrowth, perception of pain, cardiovascular responses and kidney physiology. The translation of mechanical cues into cellular responses, a process known as mechanotransduction, typically takes place in specialized multiprotein structures such as cilia, cell-cell or cell-matrix adhesions. Within these structures, mechanical forces such as shear stress and membrane stretch activate mechanosensitive proteins, which set off a series of events that lead to altered cell behavior. Members of the transient receptor potential (TRP) family of cation channels are emerging as important players in mechanotransductory pathways. Localized within mechanosensory structures, they are activated by mechanical stimuli and trigger fast as well as sustained cytoskeletal responses. In this review, we will provide an overview of how TRP channels affect cytoskeletal dynamics in various mechano-regulated processes.

Polycystin-1, 2, and STIM1 interact with IP(3)R to modulate ER Ca release through the PI3K/Akt pathway

Dysregulation of Ca(2+) signaling and homeostasis has been linked to the development of ADPKD through aberrant functioning of the polycystins. In this study, we investigated the role of the polycystins in modulating Ca(2+) signaling. Expression of full-length PC1 in MDCK cells inhibited intracellular Ca(2+) release in response to ATP when compared to control cells. This phenotype correlated with reduced interaction of endogenous PC2 and IP(3)R in PC1-containing cells. We also found that endogenous STIM1 also interacted with the IP(3)R, and this interaction was enhanced by PC1 expression. Increased interaction between STIM1 and IP(3)R inhibited Ca(2+) release. PC1 regulates intracellular Ca(2+) release and the interaction of PC2-IP(3)R-STIM1 through the PI3K/Akt signaling pathway. Inhibition of the PI3K/Akt pathway in PC1 containing cells restored intracellular Ca(2+) release, increased the interaction between PC2 and IP(3)R and disrupted the STIM1-IP(3)R complex. Conversely, activation of the PI3K/Akt signaling pathway by HGF in control MDCK cells gave the reverse effects. It reduced the release of Ca(2+) to levels comparable to the PC1 cells, inhibited the association PC2 and IP(3)R, and increased the interaction between STIM and IP(3)R. Overall, our studies provide a potential mechanism for the modulation of intracellular Ca(2+) signaling by the polycystins.

Conditional deletion of Pkd1 in osteocytes disrupts skeletal mechanosensing in mice

We investigated whether polycystin-1 is a bone mechanosensor. We conditionally deleted Pkd1 in mature osteoblasts/osteocytes by crossing Dmp1-Cre with Pkd1(flox/m1Bei) mice, in which the m1Bei allele is nonfunctional. We assessed in wild-type and Pkd1-deficient mice the response to mechanical loading in vivo by ulna loading and ex vivo by measuring the response of isolated osteoblasts to fluid shear stress. We found that conditional Pkd1 heterozygotes (Dmp1-Cre;Pkd1(flox/+)) and null mice (Pkd1(Dmp1-cKO)) exhibited a ∼ 40 and ∼ 90% decrease, respectively, in functional Pkd1 transcripts in bone. Femoral bone mineral density (12 vs. 27%), trabecular bone volume (32 vs. 48%), and cortical thickness (6 vs. 17%) were reduced proportionate to the reduction of Pkd1 gene dose, as were mineral apposition rate (MAR) and expression of Runx2-II, Osteocalcin, Dmp1, and Phex. Anabolic load-induced periosteal lamellar MAR (0.58 ± 0.14; Pkd1(Dmp1-cKO) vs. 1.68 ± 0.34 μm/d; control) and increases in Cox-2, c-Jun, Wnt10b, Axin2, and Runx2-II gene expression were significantly attenuated in Pkd1(Dmp1-cKO) mice compared with controls. Application of fluid shear stress to immortalized osteoblasts from Pkd1(null/null) and Pkd1(m1Bei/m1Bei)-derived osteoblasts failed to elicit the increments in cytosolic calcium observed in wild-type controls. These data indicate that polycystin-1 is essential for the anabolic response to skeletal loading in osteoblasts/osteocytes.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.