Podocyte Glutamatergic Signaling Contributes to the Function of the Glomerular Filtration Barrier

Podocytes possess the complete machinery for glutamatergic signaling, raising the possibility that neuron-like signaling contributes to glomerular function. To test this, we studied mice and cells lacking Rab3A, a small GTPase that regulates glutamate exocytosis. In addition, we blocked the glutamate ionotropic N-methyl-d-aspartate receptor (NMDAR) with specific antagonists. In mice, the absence of Rab3A and blockade of NMDAR both associated with an increased urinary albumin/creatinine ratio. In humans, NMDAR blockade, obtained by addition of ketamine to general anesthesia, also had an albuminuric effect. In vitro, Rab3A-null podocytes displayed a dysregulated release of glutamate with higher rates of spontaneous exocytosis, explained by a reduction in Rab3A effectors resulting in freedom of vesicles from the actin cytoskeleton. In addition, NMDAR antagonism led to profound cytoskeletal remodeling and redistribution of nephrin in cultured podocytes; the addition of the agonist NMDA reversed these changes. In summary, these results suggest that glutamatergic signaling driven by podocytes contributes to the integrity of the glomerular filtration barrier and that derangements in this signaling may lead to proteinuric renal diseases.It is widely recognized that most glomerular diseases are characterized by defects of the filtration barrier, where podocytes play a central role. Mutations of single podocyte proteins have been found at the basis of human nephrotic syndromes,¹ and podocyte deletion of the same molecules causes heavy proteinuria in experimental models.^2–8Podocytes are highly ramified cells: From the cell body depart a number of primary processes, further originating secondary foot processes. Starting from these features, it has been demonstrated that podocytes share numerous similarities with neurons: They both are terminally differentiated cells, have a common cytoskeletal organization, and have a common machinery of process formation.⁹ Furthermore, a number of expression-restricted proteins, such as nephrin,² Neph1 and Neph2,¹⁰ GLEPP1,¹¹ CAT3 and EAAT2,¹² synaptopodin,¹³ drebrin,¹⁴ and Sam68-like-MP2,¹⁵ specifically belong to the podocyte and the neuron.Our group has contributed to this line of research, initially by describing in podocytes the presence of Rab3A, a small GTPase that is mostly enriched in synaptic vesicles because it tightly modulates highly regulated exocytosis by acting through a number of effector molecules, including rabphilin-3a and Synapsin-I.¹⁶ After finding that in podocytes, as it occurs in neurons, Rab3A associates to glutamate-containing vesicles along cell processes, we discovered that podocytes are equipped with a complete neuron-like glutamatergic signaling system.¹⁷ We described that podocytes possess functional synaptic-like microvesicles and renal glomeruli express cognate glutamate transporters and receptors. These properties strengthened the analogies between podocytes and neurons and offered a rational interpretation to the biochemical similarity of foot process and synaptic adhesion complexes¹⁷; however, the role played by glutamate signaling in podocytes remained unanswered, and nothing was known about its relevance to podocyte and glomerular homeostasis. To get more details on the requirement of this neuron-like system of signaling by podocytes, we first conducted a preliminary analysis on its temporal appearance during podocyte differentiation. Then we studied conditions in which it was altered, on the vesicle and on the receptor side. The vesicular component was analyzed by studying the consequences of the absence of Rab3A. On the receptor side, we antagonized the ionotropic N-methyl-d-aspartate receptor (NMDAR), that we found present in human and rodent glomeruli, as well as in podocyte cell cultures.¹⁷ Both Rab3A and NMDAR1 glomerular synthesis were also confirmed by in situ hybridization (Supplemental Figure 1) and by microarray expression data.¹⁷     

Radiofrequency thermoablation in chest wall mesenchymal hamartoma of an infant

We report on an infant presenting with a chondroid hamartoma managed with a combined conservative surgical treatment and radiofrequency thermoablation.     

Amnioexchange for fetuses with gastroschisis: is it effective?

Background/Purpose

Amniotic fluid of fetuses with gastroschisis (GS) contains inflammatory mediators, gastrointestinal, and urinary waste products. Dilution and removal of such harmful substances have been advocated to prevent damage to the herniated intestine. We evaluated the effectiveness of serial amnioexchange procedures in 8 consecutive fetuses with GS.

Methods

Amnioexchange was performed bimonthly during the third trimester. Amniotic fluid collected before each procedure was tested for pH, osmolarity, urea, creatinine, cystatin-C, proteins, albumin, bilirubin, biliary salts, pancreatic amylase, serum amyloid A, C-reactive protein, alanine transaminase (ALT), alcaline phosphatase (ALP), gamma-glutamyl transpetidase (γGT), tumor necrosis factor α, interleukin 2, interleukin 6, epidermal growth factor, transforming growth factor β, and myeloperoxidase.

Results

A total of 25 samples (median, 3 per fetus) were examined. Biochemical or inflammatory markers did not correlate with gestational age, nor was any trend observed in values from individual patients during the course of amnioexchange treatment. There was no correlation between biochemical or inflammatory markers and clinical outcome, including time to full enteral feeding.

Conclusions

Serial amnioexchanges did not modify the biochemical or inflammatory status of amniotic fluid nor appeared to prevent injury to the herniated gut. Because repeated amnioexchanges may carry some risks, their use in fetuses with GS is not recommended outside the setting of a prospective randomized trial.     

International expert consensus on primary systemic therapy in the management of early breast cancer: highlights of the Fourth Symposium on Primary Systemic Therapy in the Management of Operable Breast Cancer, Cremona, Italy (2010)

A panel of international breast cancer experts formulated a declaration of consensus regarding many key issues in the use of primary systemic therapy (PST) either in clinical routine or research practice. The attainment of pathological complete response (pCR), defined as no residual invasive tumor in the surgical specimens both in breast and in axillary nodes, is one of the main goals of PST, and pCR can be used as the primary objective in prospective clinical trials. However, pCR is not a reliable endpoint with all treatment approaches, and alternatives such as Ki67 index of the residual invasive disease or after 2 weeks of PST are also potential endpoints. PST has several advantages: breast conservation and the unique opportunity to obtain information on the interaction between treatment and tumor biology. Changes in tumor biology after PST are an early phenomenon; so, an additional core biopsy performed after 14 days from treatment start should be considered in clinical trials.     

Trigemino-cervical reflex abnormalities in patients with migraine and cluster headache

BACKGROUND: Head pain arises within the trigeminal nociceptive system. Current theories propose that the trigeminal system is intimately involved in the pathogenesis of migraine. Short-latency responses can be recorded in sternocleidomastoid muscles after stimulation of the trigeminal nerve (trigemino-cervical reflex). This brainstem reflex could be a suitable method to evaluate the trigeminal system in migraine and CH. OBJECTIVE: The aim of the present study was to further elucidate the pathophysiology of migraine and cluster headache (CH) with special reference to the involvement of the central trigeminal system in the different forms of primary headache. METHODS: The trigemino-cervical reflex was investigated in 15 healthy subjects, in 15 patients having migraine with aura, in 15 patients with migraine without aura, and in 10 patients with CH. RESULTS: Significant abnormalities were observed in a great number of patients with both types of migraine and CH during the headache attacks, but only in migraine patients during the interictal period. The alterations are bilateral in migraine, unilateral in CH. CONCLUSIONS: Our results further support the relevance of brainstem mechanisms in the pathogenesis of migraine rather than of CH. These data, taken together with that from experimental head pain and functional imaging studies, demonstrate that primary headache syndromes may be distinguished on a functional basis by areas of activation specific to the clinical syndrome.     

Urine erythrocyte morphology in patients with microscopic haematuria caused by a glomerulopathy

The evaluation of urinary erythrocyte morphology (UEM) has been proposed for patients with isolated microscopic haematuria (IMH) to early orientate the diagnosis towards a glomerular or a nonglomerular disease. However, to date, the role of this test in patients with IMH has very rarely been investigated. Sixteen patients (ten children, six adults) with persistent IMH classified as glomerular on the basis of repeated UEM evaluations (55 urine samples, two to eight per patient) were submitted to renal biopsy. This showed a glomerular disease in 14/16 patients (87.5%) (nine thin basement membrane disease; three Alport syndrome; two other), whereas in two patients, no abnormalities were found. Of four microscopic criteria investigated to define a IMH as glomerular, >80% dysmorphic erythrocytes were not found in any sample, >or=40% dysmorphic erythrocytes alone were seen in seven samples (12.7%), >or=5% acanthocytes alone in 15 samples (27.3%) and erythrocytic casts in six samples (10.9%). There was >or=40% dysmorphic erythrocytes associated with >or=5% acanthocytes in 25 samples (45.5%). Sensitivity and positive predictive values in diagnosing a glomerular haematuria were 59.2% and 90.6%, respectively, for >or=40% dysmorphic erythrocytes, 69.4% and 85% for >or=5% acanthocytes/G1 cells and 12.2% and 100% for erythrocytic casts. Our findings demonstrate that the evaluation of UEM is useful to identify patients with an IMH of glomerular origin.     

“White dot syndromes”, an inappropriate and outdated misnomer

International Ophthalmology -