Assessment of MALDI matrices for the detection and visualization of phosphatidylinositols and phosphoinositides in mouse kidneys through matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI)

Phosphatidylinositols and their phosphorylated derivatives, known as phosphoinositides, are crucial in cellular processes, with their abnormalities linked to various diseases. Thus, identifying and measuring phosphoinositide levels in tissues are crucial for understanding their contributions to cellular processes and disease development. One powerful technique for mapping the spatial distribution of molecules in biological samples is matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). This technique allows for the simultaneous detection and analysis of multiple lipid classes in situ, making it invaluable for unbiased lipidomic studies. However, detecting phosphoinositides with MALDI-MSI is challenging due to their relatively low abundance in tissues and complex matrix effects. Addressing this, our study focused on optimizing matrix selection and thickness for better detection of phosphatidylinositols and their phosphorylated forms in mouse kidney tissues. Various matrices were assessed, including 9AA, DAN, CMBT, and DHA, adjusting their coating to improve ionization efficiency. Our results demonstrate that DAN, DHA, and CMBT matrices produced high-intensity chemical images of phosphatidylinositol distributions within kidney sections. These matrices, particularly DAN, DHA, and CMBT, allowed the identification of even low-abundance phosphoinositides, through tentative identifications. Notably, DAN and DHA served as optimal candidates due to their prominent detection and ability to map a majority of phosphatidylinositol species, while CMBT showed potential detection capability for phosphatidylinositol triphosphate compounds. These findings not only provide valuable insights for future research on the involvement of phosphoinositides in kidney pathophysiology, but also propose the use of the identified optimal matrices, particularly DAN and DHA, as the preferred choices for enhanced detection and mapping of these lipid species in future studies.

Severe kidney dysfunction in sialidosis mice reveals an essential role for neuraminidase 1 in reabsorption

Sialidosis is an ultra-rare multisystemic lysosomal disease caused by mutations in the neuraminidase 1 (NEU1) gene. The severe type II form of the disease manifests with a prenatal/infantile or juvenile onset, bone abnormalities, severe neuropathology, and visceromegaly. A subset of these patients present with nephrosialidosis, characterized by abrupt onset of fulminant glomerular nephropathy. We studied the pathophysiological mechanism of the disease in 2 NEU1-deficient mouse models, a constitutive Neu1-knockout, Neu1ΔEx3, and a conditional phagocyte-specific knockout, Neu1Cx3cr1ΔEx3. Mice of both strains exhibited terminal urinary retention and severe kidney damage with elevated urinary albumin levels, loss of nephrons, renal fibrosis, presence of storage vacuoles, and dysmorphic mitochondria in the intraglomerular and tubular cells. Glycoprotein sialylation in glomeruli, proximal distal tubules, and distal tubules was drastically increased, including that of an endocytic reabsorption receptor megalin. The pool of megalin bearing O-linked glycans with terminal galactose residues, essential for protein targeting and activity, was reduced to below detection levels. Megalin levels were severely reduced, and the protein was directed to lysosomes instead of the apical membrane. Together, our results demonstrated that desialylation by NEU1 plays a crucial role in processing and cellular trafficking of megalin and that NEU1 deficiency in sialidosis impairs megalin-mediated protein reabsorption.

Sublimation application of 5-chloro-2-mercaptobenzothiazole matrix for matrix-assisted laser desorption/ionization mass spectrometry imaging of mouse kidney

RATIONALE

Sublimation is a solvent-free technique used to apply a uniform matrix coating over a large sample plate, improving the matrix's purity and enhancing the analyte signal. Although the 5-chloro-2-mercaptobenzothiazole (CMBT) matrix was introduced years ago, there are no reports of its application via sublimation. We investigated the experimental parameters that are optimal for CMBT matrix sublimation on mouse kidney samples. We also evaluated the stability of the sublimed CMBT matrix under a vacuum environment. Using kidney samples prepared with a sublimated CMBT matrix, we conducted matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) analysis of specific phospholipids (phosphatidylcholine and phosphatidylglycerol in the positive ion mode and phosphatidylinositol in the negative ion mode). We also explored various spatial resolutions (50, 20, and 10 μm) and performed sequential MALDI-hematoxylin and eosin (H&E) staining.

METHODS

The CMBT matrix was applied to kidney samples using a sublimation apparatus connected to a vacuum pump to achieve a pressure of 0.05 Torr. The matrix was then subjected to different temperatures and sublimation times to determine the optimal conditions for matrix application. Subsequently, a Q-Exactive mass spectrometer equipped with a Spectroglyph MALDI ion source was employed for MALDI-MSI experiments. Standard protocols were followed for H&E staining after MALDI analysis.

RESULTS

A matrix thickness of 0.15 mg/cm² yielded high-quality images. The sublimated matrix exhibited minimal loss after approximately 20 h of exposure to a vacuum of 7 Torr, indicating its stability under these conditions. Ion images were successfully obtained at spatial resolutions of 50, 20, and 10 μm. Furthermore, orthogonal histological information was obtained through sequential MALDI-H&E staining.

CONCLUSIONS

We demonstrate that samples prepared for MALDI-MSI using sublimation to apply the CMBT matrix yield high-quality mass spectrometric images of mouse kidney sections. We also provide data for the impact of various experimental parameters on image quality (e.g., temperature, time, matrix thickness, and spatial resolution).

A Guide for Adult Nephrologists and Hematologists to Managing Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy in Teens Transitioning to Young Adults

Atypical hemolytic uremic syndrome and C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis are ultra-rare chronic, complement-mediated diseases with childhood manifestation in a majority of cases. Transition of clinical care of patients from pediatric to adult nephrologists-typically with controlled disease in native or transplant kidneys in case of atypical hemolytic uremic syndrome and often with chronic progressive disease despite treatment efforts in case of C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis-identifies a challenging juncture in the journey of these patients. Raising awareness for the vulnerability of this patient cohort; providing education on disease pathophysiology and management including the use of new, high-precision complement antagonists; and establishing an ongoing dialog of patients, families, and all members of the health care team involved on either side of the age divide will be inevitable to ensure optimal patient outcomes and a safe transition of these patients to adulthood.

Inherited Kidney Complement Diseases

In the past 20 years, we have witnessed tremendous advances in our ability to diagnose and treat genetic diseases of the kidney caused by complement dysregulation. Staggering progress was realized toward a better understanding of the genetic underpinnings and pathophysiology of many forms of atypical hemolytic uremic syndrome (aHUS) and C3-dominant glomerulopathies that are driven by complement system abnormalities. Many of these seminal discoveries paved the way for the design and characterization of several innovative therapies, some of which have already radically improved patients' outcomes. This review offers a broad overview of the exciting developments that have occurred in the recent past, with a particular focus on single-gene (or Mendelian), complement-driven aHUS and C3-dominant glomerulopathies that should be of interest to both nephrologists and kidney researchers. The discussion is restricted to genes with robust associations with both aHUS and C3-dominant glomerulopathies (complement factor H, complement component 3, complement factor H-related proteins) or only aHUS (complement factor B, complement factor I, and membrane cofactor protein). Key questions and challenges are highlighted, along with potential avenues for future directions.

Inherited Kidney Complement Diseases

In the past 20 years, we have witnessed tremendous advances in our ability to diagnose and treat genetic diseases of the kidney caused by complement dysregulation. Staggering progress was realized toward a better understanding of the genetic underpinnings and pathophysiology of many forms of atypical hemolytic uremic syndrome (aHUS) and C3-dominant glomerulopathies that are driven by complement system abnormalities. Many of these seminal discoveries paved the way for the design and characterization of several innovative therapies, some of which have already radically improved patients' outcomes. This review offers a broad overview of the exciting developments that have occurred in the recent past, with a particular focus on single-gene (or Mendelian), complement-driven aHUS and C3-dominant glomerulopathies that should be of interest to both nephrologists and kidney researchers. The discussion is restricted to genes with robust associations with both aHUS and C3-dominant glomerulopathies (complement factor H, complement component 3, complement factor H-related proteins) or only aHUS (complement factor B, complement factor I, and membrane cofactor protein). Key questions and challenges are highlighted, along with potential avenues for future directions.

The Phenotypic Spectrum of Tuberous Sclerosis Complex: A Canadian Cohort

Objective

We aimed to further elucidate the phenotypic spectrum of Tuberous Sclerosis Complex (TSC) depending on genotype.

Methods

A retrospective review of patients seen in the TSC clinic at the Hospital for Sick Children was conducted and the frequency of TSC manifestations was compared based on genotype.

Results

Nineteen-patients had TSC1 mutations, 36 had TSC2 mutations and 11 had no mutation identified (NMI). Patients with TSC2 mutations had a higher frequency of early-onset epilepsy and more frequent systemic manifestations. The NMI group had milder neurologic and systemic manifestations. Our data did not demonstrate that intellectual disability and infantile spasms were more common in TSC2 mutations.

Conclusions

This is the first Canadian pediatric cohort exploring the genotype-phenotype relationship in TSC. We report that some manifestations are more frequent and severe in TSC2 mutations and that NMI may have a milder phenotype. Disease surveillance and counseling should continue regardless of genotype until this is better elucidated.

Gain-of-function variants in SYK cause immune dysregulation and systemic inflammation in humans and mice

Spleen tyrosine kinase (SYK) is a critical immune signaling molecule and therapeutic target. We identified damaging monoallelic SYK variants in six patients with immune deficiency, multi-organ inflammatory disease such as colitis, arthritis and dermatitis, and diffuse large B cell lymphomas. The SYK variants increased phosphorylation and enhanced downstream signaling, indicating gain of function. A knock-in (SYK-Ser544Tyr) mouse model of a patient variant (p.Ser550Tyr) recapitulated aspects of the human disease that could be partially treated with a SYK inhibitor or transplantation of bone marrow from wild-type mice. Our studies demonstrate that SYK gain-of-function variants result in a potentially treatable form of inflammatory disease.

Canadian Association of Paediatric Nephrologists COVID-19 Rapid Response: Guidelines for Management of Acute Kidney Injury in Children

PURPOSE

This article provides guidance on managing acute kidney injury (AKI) and kidney replacement therapy (KRT) in pediatrics during the COVID-19 pandemic in the Canadian context. It is adapted from recently published rapid guidelines on the management of AKI and KRT in adults, from the Canadian Society of Nephrology (CSN). The goal is to provide the best possible care for pediatric patients with kidney disease during the pandemic and ensure the health care team's safety.

INFORMATION SOURCES

The Canadian Association of Paediatric Nephrologists (CAPN) COVID-19 Rapid Response team derived these rapid guidelines from the CSN consensus recommendations for adult patients with AKI. We have also consulted specific documents from other national and international agencies focused on pediatric kidney health. We identified additional information by reviewing the published academic literature relevant to pediatric AKI and KRT, including recent journal articles and preprints related to COVID-19 in children. Finally, our group also sought expert opinions from pediatric nephrologists across Canada.

METHODS

The leadership of the CAPN, which is affiliated with the CSN, solicited a team of clinicians and researchers with expertise in pediatric AKI and acute KRT. The goal was to adapt the guidelines recently adopted for Canadian adult patients for pediatric-specific settings. These included specific COVID-19-related themes relevant to AKI and KRT in a Canadian setting, as determined by a group of kidney disease experts and leaders. An expert group of clinicians in pediatric AKI and acute KRT reviewed the revised pediatric guidelines.

KEY FINDINGS

(1) Current Canadian data do not suggest an imminent threat of an increase in acute KRT needs in children because of COVID-19; however, close coordination between nephrology programs and critical care programs is crucial as the pandemic continues to evolve. (2) Pediatric centers should prepare to reallocate resources to adult centers as needed based on broader health care needs during the COVID-19 pandemic. (3) Specific suggestions pertinent to the optimal management of AKI and KRT in COVID-19 patients are provided. These suggestions include but are not limited to aspects of fluid management, KRT vascular access, and KRT modality choice. (4) Considerations to ensure adequate provision of KRT if resources become scarce during the COVID-19 pandemic.

LIMITATIONS

We did not conduct a formal systematic review or meta-analysis. We did not evaluate our specific suggestions in the clinical environment. The local context, including how the provision of care for AKI and acute KRT is organized, may impede the implementation of many suggestions. As knowledge is advancing rapidly in the area of COVID-19, suggestions may become outdated quickly. Finally, most of the literature for AKI and KRT in COVID-19 comes from adult data, and there are few pediatric-specific studies.

IMPLICATIONS

Given that most acute KRT related to COVID-19 is likely to be required in the pediatric intensive care unit initial setting, close collaboration and planning between critical care and pediatric nephrology programs are needed. Our group will update these suggestions with a supplement if necessary as newer evidence becomes available that may change or add to the recommendations provided.

Rho-GTPase Activating Protein myosin MYO9A identified as a novel candidate gene for monogenic focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a podocytopathy leading to kidney failure, whose molecular cause frequently remains unresolved. Here, we describe a rare MYO9A loss of function nonsense heterozygous mutation (p.Arg701^∗) as a possible contributor to disease in a sibling pair with familial FSGS/proteinuria. MYO9A variants of uncertain significance were identified by whole exome sequencing in a cohort of 94 biopsy proven patients with FSGS. MYO9A is an unconventional myosin with a Rho-GAP domain that controls epithelial cell junction assembly, crosslinks and bundles actin and deactivates the small GTPase protein encoded by the RHOA gene. RhoA activity is associated with cytoskeleton regulation of actin stress fiber formation and actomyosin contractility. Myo9A was detected in mouse and human podocytes in vitro and in vivo. Knockin mice carrying the p.Arg701^∗MYO9A (Myo9A^R701X) generated by gene editing developed proteinuria, podocyte effacement and FSGS. Kidneys and podocytes from Myo9A^R701X/+ mutant mice revealed Myo9A haploinsufficiency, increased RhoA activity, decreased Myo9A-actin-calmodulin interaction, impaired podocyte attachment and migration. Our results indicate that Myo9A is a novel component of the podocyte cytoskeletal apparatus that regulates RhoA activity and podocyte function. Thus, Myo9A^R701X/+ knock-in mice recapitulate the proband FSGS phenotype, demonstrate that p.R701X Myo9A is an FSGS-causing mutation in mice and suggest that heterozygous loss-of-function MYO9A mutations may cause a novel form of human autosomal dominant FSGS. Hence, identification of MYO9A pathogenic variants in additional individuals with familial or sporadic FSGS is needed to ascertain the gene contribution to disease.

Canadian Association of Paediatric Nephrologists COVID-19 Rapid Response: Home and In-Center Dialysis Guidance

PURPOSE OF THE PROGRAM

This article provides guidance on optimizing the management of pediatric patients with end-stage kidney disease (ESKD) who will be or are being treated with any form of home or in-center dialysis during the COVID-19 pandemic. The goals are to provide the best possible care for pediatric patients with ESKD during the pandemic and ensure the health care team's safety.

SOURCES OF INFORMATION

The core of these rapid guidelines is derived from the Canadian Society of Nephrology (CSN) consensus recommendations for adult patients recently published in the Canadian Journal of Kidney Health and Disease (CJKHD). We also consulted specific documents from other national and international agencies focused on pediatric kidney health. Additional information was obtained by formal review of the published academic literature relevant to pediatric home or in-center hemodialysis.

METHODS

The Leadership of the Canadian Association of Paediatric Nephrologists (CAPN), which is affiliated with the CSN, solicited a team of clinicians and researchers with expertise in pediatric home and in-center dialysis. The goal was to adapt the guidelines recently adopted for Canadian adult dialysis patients for pediatric-specific settings. These included specific COVID-19-related themes that apply to dialysis in a Canadian environment, as determined by a group of senior renal leaders. Expert clinicians and nurses with deep expertise in pediatric home and in-center dialysis reviewed the revised pediatric guidelines.

KEY FINDINGS

We identified 7 broad areas of home dialysis practice management that may be affected by the COVID-19 pandemic: (1) peritoneal dialysis catheter placement, (2) home dialysis training, (3) home dialysis management, (4) personal protective equipment, (5) product delivery, (6) minimizing direct health care providers and patient contact, and (7) caregivers support in the community. In addition, we identified 8 broad areas of in-center dialysis practice management that may be affected by the COVID-19 pandemic: (1) identification of patients with COVID-19, (2) hemodialysis of patients with confirmed COVID-19, (3) hemodialysis of patients not yet known to have COVID-19, (4) management of visitors to the dialysis unit, (5) handling COVID-19 testing of patients and staff, (6) safe practices during resuscitation procedures in a pandemic, (7) routine hemodialysis care, and (8) hemodialysis care under fixed dialysis resources. We make specific suggestions and recommendations for each of these areas.

LIMITATIONS

At the time when we started this work, we knew that evidence on the topic of pediatric dialysis and COVID-19 would be severely limited, and our resources were also limited. We did not, therefore, do formal systematic review or meta-analysis. We did not evaluate our specific suggestions in the clinical environment. Thus, this article's advice and recommendations are primarily expert opinions and subject to the biases associated with this level of evidence. To expedite the publication of this work, we created a parallel review process that may not be as robust as standard arms' length peer-review processes.

IMPLICATIONS

We intend these recommendations to help provide the best care possible for pediatric patients prescribed in-center or home dialysis during the COVID-19 pandemic, a time of altered priorities and reduced resources.

Novel Fanconi renotubular syndromes provide insights in proximal tubule pathophysiology

The various forms of Fanconi renotubular syndromes (FRTS) offer significant challenges for clinicians and present unique opportunities for scientists who study proximal tubule physiology. This review will describe the clinical characteristics, genetic underpinnings, and underlying pathophysiology of the major forms of FRST. Although the classic forms of FRTS will be presented (e.g., Dent disease or Lowe syndrome), particular attention will be paid to five of the most recently discovered FRTS subtypes caused by mutations in the genes encoding for L-arginine:glycine amidinotransferase (GATM), solute carrier family 34 (type Ii sodium/phosphate cotransporter), member 1 (SLC34A1), enoyl-CoAhydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), hepatocyte nuclear factor 4A (HNF4A), or NADH dehydrogenase complex I, assembly factor 6 (NDUFAF6). We will explore how mutations in these genes revealed unexpected mechanisms that led to compromised proximal tubule functions. We will also describe the inherent challenges associated with gene discovery studies based on findings derived from small, single-family studies by focusing the story of FRTS type 2 (SLC34A1). Finally, we will explain how extensive alternative splicing of HNF4A has resulted in confusion with mutation nomenclature for FRTS type 4.

Management of Canadian Pediatric Patients With Glomerular Diseases During the COVID-19 Pandemic: Recommendations From the Canadian Association of Pediatric Nephrologists COVID-19 Rapid Response Team

Purpose

The goal of these recommendations is to provide guidance on the optimal care of children with glomerular diseases during the COVID-19 pandemic. Patients with glomerular diseases are known to be more susceptible to infection. Risk factors include decreased vaccine uptake, urinary loss of immunoglobulins, and treatment with immunosuppressive medications. The Canadian Society of Nephrology (CSN) recently published guidelines on the care of adult glomerulonephritis patients. This guideline aims to expand and adapt those recommendations for programs caring for children with glomerular diseases.

Sources of information

We used the CSN COVID-19 Rapid Response Team adult glomerulonephritis recommendations, published in the Canadian Journal of Kidney Health and Disease, as the foundation for our guidelines. We reviewed documents published by nephrology and non-nephrology societies and health care agencies focused on kidney disease and immunocompromised populations. Finally, we conducted a formal literature review of publications relevant to pediatric and adult glomerular disease, chronic kidney disease, hypertension, and immunosuppression in the context of the COVID-19 pandemic.

Methods

The leadership of the Canadian Association of Pediatric Nephrologists (CAPN), which is affiliated with the CSN, identified a team of clinicians and researchers with expertise in pediatric glomerular diseases. The aim was to adapt Canadian adult glomerulonephritis guidelines to make them applicable to children and discuss pediatric-specific considerations. The updated guidelines were peer-reviewed by senior clinicians with expertise in the care of childhood glomerular diseases.

Key findings

We identified a number of key areas of glomerular disease care likely to be affected by the COVID-19 pandemic, including (1) clinic visit scheduling, (2) visit types, (3) provision of multidisciplinary care, (4) blood work and imaging, (5) home monitoring, (6) immunosuppression, (7) other medications, (8) immunizations, (9) management of children with suspected COVID-19, (10) renal biopsy, (11) patient education and support, and (12) school and child care.

Limitations

There are minimal data regarding the characteristics and outcomes of COVID-19 in adult or pediatric glomerular disease patients, as well as the efficacy of strategies to prevent infection transmission within these populations. Therefore, the majority of these recommendations are based on expert opinion and consensus guidance. To expedite the publication of these guidelines, an internal peer-review process was conducted, which may not have been as rigorous as formal journal peer-review.

Implications

These guidelines are intended to promote optimal care delivery for children with existing or newly diagnosed glomerular diseases during the COVID-19 pandemic. The implications of modified care delivery, altered immunosuppression strategies, and limited access to existing resources remain uncertain.

The pupil: a window on social automatic processing in autism spectrum disorder children

BACKGROUND

Faces are crucial social stimuli, eliciting automatic processing associated with increased physiological arousal in observers. The level of arousal can be indexed by pupil diameter (the 'Event-Related Pupil Dilation', ERPD). However, many parameters could influence the arousal evoked by a face and its social saliency (e.g. virtual vs. real, neutral vs. emotional, static vs. dynamic). A few studies have shown an atypical ERPD in autism spectrum disorder (ASD) patients using several kinds of faces but no study has focused on identifying which parameter of the stimulus is the most interfering with face processing in ASD.

METHODS

In order to disentangle the influence of these parameters, we propose an original paradigm including stimuli along an ecological social saliency gradient: from static objects to virtual faces to dynamic emotional faces. This strategy was applied to 186 children (78 ASD and 108 typically developing (TD) children) in two pupillometric studies (22 ASD and 47 TD children in the study 1 and 56 ASD and 61 TD children in the study 2).

RESULTS

Strikingly, the ERPD in ASD children is insensitive to any of the parameters tested: the ERPD was similar for objects, static faces or dynamic faces. On the opposite, the ERPD in TD children is sensitive to all the parameters tested: the humanoid, biological, dynamic and emotional quality of the stimuli. Moreover, ERPD had a good discriminative power between ASD and TD children: ASD had a larger ERPD than TD in response to virtual faces, while TD had a larger ERPD than ASD for dynamic faces.

CONCLUSIONS

This novel approach evidences an abnormal physiological adjustment to socially relevant stimuli in ASD.

SON haploinsufficiency causes impaired pre-mRNA splicing of CAKUT genes and heterogeneous renal phenotypes

Although genetic testing is increasingly used in clinical nephrology, a large number of patients with congenital abnormalities of the kidney and urinary tract (CAKUT) remain undiagnosed with current gene panels. Therefore, careful curation of novel genetic findings is key to improving diagnostic yields. We recently described a novel intellectual disability syndrome caused by de novo heterozygous loss-of-function mutations in the gene encoding the splicing factor SON. Here, we show that many of these patients, including two previously unreported, exhibit a wide array of kidney abnormalities. Detailed phenotyping of 14 patients with SON haploinsufficiency identified kidney anomalies in 8 patients, including horseshoe kidney, unilateral renal hypoplasia, and renal cysts. Recurrent urinary tract infections, electrolyte disturbances, and hypertension were also observed in some patients. SON knockdown in kidney cell lines leads to abnormal pre-mRNA splicing, resulting in decreased expression of several established CAKUT genes. Furthermore, these molecular events were observed in patient-derived cells with SON haploinsufficiency. Taken together, our data suggest that the wide spectrum of phenotypes in patients with a pathogenic SON mutation is a consequence of impaired pre-mRNA splicing of several CAKUT genes. We propose that genetic testing panels designed to diagnose children with a kidney phenotype should include the SON gene.

Opportunities and Challenges for Genetic Studies of End-Stage Renal Disease in Canada

Purpose of review:

Genetic testing can improve diagnostic precision in some patients with end-stage renal disease (ESRD) providing the potential for targeted therapy and improved patient outcomes. We sought to describe the genetic architecture of ESRD and Canadian data sources available for further genetic investigation into ESRD.

Sources of information:

We performed PubMed searches of English, peer-reviewed articles using keywords “chronic kidney disease,” “ESRD,” “genetics,” “sequencing,” and “administrative databases,” and searched for nephrology-related Mendelian diseases on the Online Mendelian Inheritance in Man database.

Methods:

In this narrative review, we discuss our evolving understanding of the genetic architecture of kidney disease and ESRD, the risks and benefits of using genetic data to help diagnose and manage patients with ESRD, existing public Canadian biobanks and databases, and a vision for future genetic studies of ESRD in Canada.

Key findings:

ESRD has a polygenic architecture including rare Mendelian mutations and common small effect genetic polymorphism contributors. Genetic testing will improve diagnostic accuracy and contribute to a precision medicine approach in nephrology. However, the risk and benefits of genetic testing needs to be considered from an individual and societal perspective, and further research is required. Merging existing health data, linking biobanks and administrative databases, and forming Canadian collaborations hold great potential for genetic research into ESRD. Large sample sizes are necessary to perform the suitably powered investigations required to bring this vision to reality.

Limitations:

This is a narrative review of the literature discussing future directions and opportunities. It reflects the views and academic biases of the authors.

Implications:

National collaborations will be required to obtain sample sizes required for impactful, robust research. Merging established datasets may be one approach to obtain adequate samples. Patient education and engagement will improve the value of knowledge gained.

Assessment of Translocator Protein Density, as Marker of Neuroinflammation, in Major Depressive Disorder: A Pilot, Multicenter, Comparative, Controlled, Brain PET Study (INFLADEP Study)

Background: Major depressive disorder (MDD) is a serious public health problem with high lifetime prevalence (4.4-20%) in the general population. The monoamine hypothesis is the most widespread etiological theory of MDD. Also, recent scientific data has emphasized the importance of immuno-inflammatory pathways in the pathophysiology of MDD. The lack of data on the magnitude of brain neuroinflammation in MDD is the main limitation of this inflammatory hypothesis. Our team has previously demonstrated the relevance of [18F] DPA-714 as a neuroinflammation biomarker in humans. We formulated the following hypotheses for the current study: (i) Neuroinflammation in MDD can be measured by [18F] DPA-714; (ii) its levels are associated with clinical severity; (iii) it is accompanied by anatomical and functional alterations within the frontal-subcortical circuits; (iv) it is a marker of treatment resistance. Methods: Depressed patients will be recruited throughout 4 centers (Bordeaux, Montpellier, Tours, and Toulouse) of the French network from 13 expert centers for resistant depression. The patient population will be divided into 3 groups: (i) experimental group-patients with current MDD (n = 20), (ii) remitted depressed group-patients in remission but still being treated (n = 20); and, (iii) control group without any history of MDD (n = 20). The primary objective will be to compare PET data (i.e., distribution pattern of neuroinflammation) between the currently depressed group and the control group. Secondary objectives will be to: (i) compare neuroinflammation across groups (currently depressed group vs. remitted depressed group vs. control group); (ii) correlate neuroinflammation with clinical severity across groups; (iii) correlate neuroinflammation with MRI parameters for structural and functional integrity across groups; (iv) correlate neuroinflammation and peripheral markers of inflammation across groups. Discussion: This study will assess the effects of antidepressants on neuroinflammation as well as its role in the treatment response. It will contribute to clarify the putative relationships between neuroinflammation quantified by brain neuroimaging techniques and peripheral markers of inflammation. Lastly, it is expected to open innovative and promising therapeutic perspectives based on anti-inflammatory strategies for the management of treatment-resistant forms of MDD commonly seen in clinical practice. Clinical trial registration (reference: NCT03314155): https://www.clinicaltrials.gov/ct2/show/NCT03314155?term=neuroinflammation&cond=depression&cntry=FR&rank=1.

The Phenotypic Spectrum of Nephropathies Associated with Mutations in Diacylglycerol Kinase ε

The recent discovery of mutations in the gene encoding diacylglycerol kinase ε (DGKE) identified a novel pathophysiologic mechanism leading to HUS and/or MPGN. We report ten new patients from eight unrelated kindreds with DGKE nephropathy. We combined these cases with all previously published cases to characterize the phenotypic spectrum and outcomes of this new disease entity. Most patients presented with HUS accompanied by proteinuria, whereas a subset of patients exhibited clinical and histologic patterns of MPGN without TMA. We also report the first two patients with clinical and histologic HUS/MPGN overlap. DGKE-HUS typically manifested in the first year of life but was not exclusively limited to infancy, and viral triggers frequently preceded HUS episodes. We observed signs of complement activation in some patients with DGKE-HUS, but the role of complement activation remains unclear. Most patients developed a slowly progressive proteinuric nephropathy: 80% of patients did not have ESRD within 10 years of diagnosis. Many patients experienced HUS remission without specific treatment, and a few patients experienced HUS recurrence despite complete suppression of the complement pathway. Five patients received renal allografts, with no post-transplant recurrence reported. In conclusion, we did not observe a clear genotype-phenotype correlation in patients with DGKE nephropathy, suggesting additional factors mediating phenotypic heterogeneity. Furthermore, the benefits of anti-complement therapy are questionable but renal transplant may be a feasible option in the treatment of patients with this condition.

A variant in a cis-regulatory element enhances claudin-14 expression and is associated with pediatric-onset hypercalciuria and kidney stones

The greatest risk factor for kidney stones is hypercalciuria, the etiology of which is largely unknown. A recent genome-wide association study (GWAS) linked hypercalciuria and kidney stones to a claudin-14 (CLDN14) risk haplotype. However, the underlying molecular mechanism was not delineated. Recently, renal CLDN14 expression was found to increase in response to increased plasma calcium, thereby inducing calciuria. We hypothesized therefore that some children with hypercalciuria and kidney stones harbor a CLDN14 variant that inappropriately increases gene expression. To test this hypothesis, we sequenced the CLDN14 risk haplotype in a cohort of children with idiopathic hypercalciuria and kidney stones. An intronic SNP was more frequent in affected children. Dual luciferase and cell-based assays demonstrated increased reporter or CLDN14 expression when this polymorphism was introduced. In silico studies predicted the SNP introduced a novel insulinoma-associated 1 (INSM1) transcription factor binding site. Consistent with this, repeating the dual luciferase assay in the presence of INSM1 further increased reporter expression. Our data suggest that children with the INSM1 binding site within the CLDN14 risk haplotype have a higher likelihood of hypercalciuria and kidney stones. Enhanced CLDN14 expression may play a role in the pathophysiology of their hypercalciuria.

Diacylglycerol Kinase-ε: Properties and Biological Roles

In mammals there are at least 10 isoforms of diacylglycerol kinases (DGK). All catalyze the phosphorylation of diacylglycerol (DAG) to phosphatidic acid (PA). Among DGK isoforms, DGKε has several unique features. It is the only DGK isoform with specificity for a particular species of DAG, i.e., 1-stearoyl-2-arachidonoyl glycerol. The smallest of all known DGK isoforms, DGKε, is also the only DGK devoid of a regulatory domain. DGKε is the only DGK isoform that has a hydrophobic segment that is predicted to form a transmembrane helix. As the only membrane-bound, constitutively active DGK isoform with exquisite specificity for particular molecular species of DAG, the functional overlap between DGKε and other DGKs is predicted to be minimal. DGKε exhibits specificity for DAG containing the same acyl chains as those found in the lipid intermediates of the phosphatidylinositol-cycle. It has also been shown that DGKε affects the acyl chain composition of phosphatidylinositol in whole cells. It is thus likely that DGKε is responsible for catalyzing one step in the phosphatidylinositol-cycle. Steps of this cycle take place in both the plasma membrane and the endoplasmic reticulum membrane. DGKε is likely present in both of these membranes. DGKε is the only DGK isoform that is associated with a human disease. Indeed, recessive loss-of-function mutations in DGKε cause atypical hemolytic-uremic syndrome (aHUS). This condition is characterized by thrombosis in the small vessels of the kidney. It causes acute renal insufficiency in infancy and most patients develop end-stage renal failure before adulthood. Disease pathophysiology is poorly understood and there is no therapy. There are also data suggesting that DGKε may play a role in epilepsy and Huntington disease. Thus, DGKε has many unique molecular and biochemical properties when compared to all other DGK isoforms. DGKε homologs also contain a number of conserved sequence features that are distinctive characteristics of either the rodents or specific groups of primate homologs. How cells, tissues and organisms harness DGKε's catalytic prowess remains unclear. The discovery of DGKε's role in causing aHUS will hopefully boost efforts to unravel the mechanisms by which DGKε dysfunction causes disease.

Diacylglycerol Kinase-ε: Properties and Biological Roles

In mammals there are at least 10 isoforms of diacylglycerol kinases (DGK). All catalyze the phosphorylation of diacylglycerol (DAG) to phosphatidic acid (PA). Among DGK isoforms, DGKε has several unique features. It is the only DGK isoform with specificity for a particular species of DAG, i.e., 1-stearoyl-2-arachidonoyl glycerol. The smallest of all known DGK isoforms, DGKε, is also the only DGK devoid of a regulatory domain. DGKε is the only DGK isoform that has a hydrophobic segment that is predicted to form a transmembrane helix. As the only membrane-bound, constitutively active DGK isoform with exquisite specificity for particular molecular species of DAG, the functional overlap between DGKε and other DGKs is predicted to be minimal. DGKε exhibits specificity for DAG containing the same acyl chains as those found in the lipid intermediates of the phosphatidylinositol-cycle. It has also been shown that DGKε affects the acyl chain composition of phosphatidylinositol in whole cells. It is thus likely that DGKε is responsible for catalyzing one step in the phosphatidylinositol-cycle. Steps of this cycle take place in both the plasma membrane and the endoplasmic reticulum membrane. DGKε is likely present in both of these membranes. DGKε is the only DGK isoform that is associated with a human disease. Indeed, recessive loss-of-function mutations in DGKε cause atypical hemolytic-uremic syndrome (aHUS). This condition is characterized by thrombosis in the small vessels of the kidney. It causes acute renal insufficiency in infancy and most patients develop end-stage renal failure before adulthood. Disease pathophysiology is poorly understood and there is no therapy. There are also data suggesting that DGKε may play a role in epilepsy and Huntington disease. Thus, DGKε has many unique molecular and biochemical properties when compared to all other DGK isoforms. DGKε homologs also contain a number of conserved sequence features that are distinctive characteristics of either the rodents or specific groups of primate homologs. How cells, tissues and organisms harness DGKε's catalytic prowess remains unclear. The discovery of DGKε's role in causing aHUS will hopefully boost efforts to unravel the mechanisms by which DGKε dysfunction causes disease.

Diacylglycerol kinase epsilon suppresses expression of p53 and glycerol kinase in mouse embryo fibroblasts

The incorporation of glycerol into lipid was measured using SV40 transformed mouse embryo fibroblasts (MEFs) from either wild-type (WT) mice or from mice in which the epsilon isoform of diacylglycerol kinase (DGKε) was knocked out (DGKε^-/-). We present an explanation for our finding that DGKε^-/- MEFs exhibited greater uptake of ³H-glycerol into the cell and a greater incorporation into lipids compared with their WT counterparts, with no change in the relative amounts of various lipids between the DGKε^-/- and WT MEFs. Glycerol kinase is more highly expressed in the DGKε^-/- cells than in their WT counterparts. In addition, the activity of glycerol kinase is greater in the DGKε^-/- cells than in their WT counterparts. Other substrates that enter the cell independent of glycerol kinase, such as pyruvate or acetate, are incorporated into lipid to the same extent between DGKε^-/- and WT cell lines. We also show that expression of p53, a transcription factor that increases the synthesis of glycerol kinase, is increased in DGKε^-/- MEFs in comparison to WT cells. We conclude that the increased incorporation of glycerol into lipids in DGKε^-/- cells is a consequence of up-regulation of glycerol kinase and not a result of an increase in the rate of lipid synthesis. Furthermore, increased expression of the pro-survival gene, p53, in cells knocked out for DGKε suggests that cells over-expressing DGKε would have a greater propensity to become tumorigenic.

Atypical Brain Mechanisms of Prediction According to Uncertainty in Autism

Resistance to change is often reported in autism and may arise from an inability to predict events in uncertain contexts. Using EEG recorded in 12 adults with autism and age-matched controls performing a visual target detection task, we characterized the influence of a certain context (targets preceded by a predictive sequence of three distinct stimuli) or an uncertain context (random targets) on behavior and electrophysiological markers of predictive processing. During an uncertain context, adults with autism were faster than controls to detect targets. They also had an enhancement in CNV amplitude preceding all random stimuli-indexing enhanced preparatory mechanisms, and an earlier N2 to targets-reflecting faster information processing-compared to controls. During a certain context, both controls and adults with autism presented an increase in P3 amplitude to predictive stimuli-indexing information encoding of the predictive sequence, an enhancement in CNV amplitude preceding predictable targets-corresponding to the deployment of preparatory mechanisms, and an earlier P3 to predictable targets-reflecting efficient prediction building and implementation. These results suggest an efficient extraction of predictive information to generate predictions in both controls and adults with autism during a certain context. However, adults with autism displayed a failure to decrease mu power during motor preparation accompanied by a reduced benefit in reaction times to predictable targets. The data reveal that patients with autism over-anticipate stimuli occurring in an uncertain context, in accord with their sense of being overwhelmed by incoming information. These results suggest that adults with autism cannot flexibly modulate cortical activity according to changing levels of uncertainty.

Increased affective reactivity to neutral stimuli and decreased maintenance of affective responses in bipolar disorder

BACKGROUND

Affective dysregulation is a core feature of bipolar disorder (BD) and a significant predictor of clinical and functional outcome. Affective dysregulation can arise from abnormalities in multiple processes. This study addresses the knowledge gap regarding the precise nature of the processes that may be dysregulated in BD and their relationship to the clinical expression of the disorder.

METHODS

Patients with BD (n=45) who were either in remission or in a depressive or manic state and healthy individuals (n=101) were compared in terms of the intensity, duration and physiological response (measured using inter-beat intervals and skin conductance) to affective and neutral pictures during passive viewing and during experiential suppression.

RESULTS

Compared to healthy individuals, patients with BD evidenced increased affective reactivity to neutral pictures and reduced maintenance of subjective affective responses to all pictures. This pattern was present irrespective of clinical state but was more pronounced in symptomatic patients, regardless of polarity. Patients, regardless of symptomatic status, were comparable to healthy individuals in terms of physiological arousal and voluntary control of affective responses.

CONCLUSION

Our study demonstrates that increased affective reactivity to neutral stimuli and decreased maintenance of affective responses are key dimensions of affective dysregulation in BD.

When Langerhans’ and Cajal’s worlds collide, diabetics win

A new antidiabetic therapy has emerged from the demonstration that a neuronal receptor expressed on pancreatic β cells tightly regulates insulin secretion after glucose exposure.

Characterization of a New DGKE Intronic Mutation in Genetically Unsolved Cases of Familial Atypical Hemolytic Uremic Syndrome

BACKGROUND AND OBJECTIVES

Genetic and acquired abnormalities causing dysregulation of the complement alternative pathway contribute to atypical hemolytic uremic syndrome (aHUS), a rare disorder characterized by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute kidney failure. However, in a substantial proportion of patients the disease-associated alterations are still unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Whole-exome and whole-genome sequencing were performed in two unrelated families with infantile recessive aHUS. Sequencing of cDNA from affected individuals was used to test for the presence of aberrant mRNA species. Expression of mutant diacylglycerol kinase epsilon (DGKE) protein was evaluated with western blotting.

RESULTS

Whole-exome sequencing analysis with conventional variant filtering parameters did not reveal any obvious candidate mutation in the first family. The report of aHUS-associated mutations in DGKE, encoding DGKE, led to re-examination of the noncoding DGKE variants obtained from next-generation sequencing, allowing identification of a novel intronic DGKE mutation (c.888+40A>G) that segregated with disease. Sequencing of cDNA from affected individuals revealed aberrant forms of DGKE mRNA predicted to cause profound abnormalities in the protein catalytic site. By whole-genome sequencing, the same mutation was found in compound heterozygosity with a second nonsense DGKE mutation in all affected siblings of another unrelated family. Homozygous and compound heterozygous patients presented similar clinical features, including aHUS presentation in the first year of life, multiple relapsing episodes, and proteinuria, which are prototypical of DGKE-associated aHUS.

CONCLUSIONS

This is the first report of a mutation located beyond the exon-intron boundaries in aHUS. Intronic mutations such as these are underreported because conventional filtering parameters used to process next-generation sequencing data routinely exclude these regions from downstream analyses in both research and clinical settings. The results suggest that analysis of noncoding regions of aHUS-associated genes coupled with mRNA sequencing might provide a tool to explain genetically unsolved aHUS cases.

Autism heritability: A new twist on familial genetics?

Analysis of whole-genome sequencing data suggests that a substantial proportion of presumed pathogenic mutations are not shared by autistic siblings.

RSV Bronchiolitis: Tale of an Overzealous Helper?

TLR4 genotypes and nasal bacterial carriage trigger an exaggerated type 2 helper T cell response during severe RSV bronchiolitis.

Superheroes and Villains of the Heart

A cardiac-specific long noncoding RNA plays a critical role in protecting humans and mice from heart failure.

Human Cells: Finally Open for Cancer Business

Insertional mutagenesis of normal human cells with a transposon-expressing lentivirus leads to better cancer cell models.

For IBD, Bugs and Genes Are the Name of the Game

Ileal microbe and tissue mRNA profiling may help provide better prognoses and therapies to treatment-naïve IBD patients.