The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

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Initial sequencing and analysis of the human genome.

Glomerular podocytes are highly specialized cells with a complex cytoarchitecture. Their most prominent features are interdigitated foot processes with filtration slits in between. These are bridged by the slit diaphragm, which plays a major role in establishing the selective permeability of the glomerular filtration barrier. Injury to podocytes leads to proteinuria, a hallmark of most glomerular diseases. New technical approaches have led to a considerable increase in our understanding of podocyte biology including protein inventory, composition and arrangement of the cytoskeleton, receptor equipment, and signaling pathways involved in the control of ultrafiltration. Moreover, disturbances of podocyte architecture resulting in the retraction of foot processes and proteinuria appear to be a common theme in the progression of acquired glomerular disease. In hereditary nephrotic syndromes identified over the last 2 years, all mutated gene products were localized in podocytes. This review integrates our recent physiological and molecular understanding of the role of podocytes during the maintenance and failure of the glomerular filtration barrier.

Cell Biology of the Glomerular Podocyte

Familial idiopathic nephrotic syndromes represent a heterogeneous group of kidney disorders, and include autosomal recessive steroid-resistant nephrotic syndrome, which is characterized by early childhood onset of proteinuria, rapid progression to end-stage renal disease and focal segmental glomerulosclerosis. A causative gene for this disease, NPHS2, was mapped to 1q25-31 and we report here its identification by positional cloning. NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family. We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier.

NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome

Focal and segmental glomerulosclerosis (FSGS) is a kidney disorder of unknown etiology, and up to 20% of patients on dialysis have been diagnosed with it. Here we show that a large family with hereditary FSGS carries a missense mutation in the TRPC6 gene on chromosome 11q, encoding the ion-channel protein transient receptor potential cation channel 6 (TRPC6). The proline-to-glutamine substitution at position 112, which occurs in a highly conserved region of the protein, enhances TRPC6-mediated calcium signals in response to agonists such as angiotensin II and appears to alter the intracellular distribution of TRPC6 protein. Previous work has emphasized the importance of cytoskeletal and structural proteins in proteinuric kidney diseases. Our findings suggest an alternative mechanism for the pathogenesis of glomerular disease.

https://science.sciencemag.org/content/sci/308/5729/1801.full.pdf

A Mutation in the TRPC6 Cation Channel Causes Familial Focal Segmental Glomerulosclerosis

Recent molecular insights have established the podocyte as a key component of the glomerular filtration barrier, and hence an important common pathway in proteinuric diseases. A conditionally immortalized human podocyte cell line has been developed by transfection with the temperature-sensitive SV40-T gene. These cells proliferate at the "permissive" temperature (33 degrees C). After transfer to the "nonpermissive" temperature (37 degrees C), they entered growth arrest and expressed markers of differentiated in vivo podocytes, including the novel podocyte proteins, nephrin, podocin, CD2AP, and synaptopodin, and known molecules of the slit diaphragm ZO-1, alpha-, beta-, and gamma-catenin and P-cadherin. The differentiation was accompanied by a growth arrest and the upregulation of cyclin-dependent kinase inhibitors, p27 and p57, as well as cyclin D(1), whereas cyclin A was downregulated. These data are consistent with cell cycle protein expression during podocyte maturation in vivo. In conclusion, the development of this cell line provides a new tool in the study of podocyte biology, which will enable accurate assessment of the behavior of these complex cells in health and disease.

A Conditionally Immortalized Human Podocyte Cell Line Demonstrating Nephrin and Podocin Expression

Focal and segmental glomerulosclerosis (FSGS) is a common, non-specific renal lesion Although it is often secondary to other disorders, including HIV infection, obesity, hypertension and diabetes, FSGS also appears as an isolated, idiopathic condition FSGS is characterized by increased urinary protein excretion and decreasing kidney function Often, renal insufficiency in affected patients progresses to end-stage renal failure, a highly morbid state requiring either dialysis therapy or kidney transplantation Here we present evidence implicating mutations in the gene encoding alpha-actinin-4 (ACTN4; ref 2), an actin-filament crosslinking protein, as the cause of disease in three families with an autosomal dominant form of FSGS In vitro, mutant alpha-actinin-4 binds filamentous actin (F-actin) more strongly than does wild-type alpha-actinin-4 Regulation of the actin cytoskeleton of glomerular podocytes may be altered in this group of patients Our results have implications for understanding the role of the cytoskeleton in the pathophysiology of kidney disease and may lead to a better understanding of the genetic basis of susceptibility to kidney damage

https://www.childrenshospital.org/~/media/research-and-innovation/research-labs/beggs-lab/pdfs/44.ashx?la=en

Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.

Synergy of sodium thiosulphate treatment and expanded hemodialysis in the management of calciphylaxis? A case report.

Chronic inflammation and the underlying cardiovascular comorbidity are still current problems in chronic hemodialysis patients. There are few studies comparing the "dialysis dose" with the degree of inflammation in the patient. Our main objective was to determine whether there is a relationship between serum C-reactive protein (CRP) levels and the "dialysis dose" (Kt / V) using ionic dialysance.Multicenter cross-sectional study. 536 prevalent chronic hemodialysis patients were included. CRP levels, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) were collected. Kt was obtained by ionic dialysance and urea distribution volume was calculated from the Watson's formula. The sample was divided into two groups, taking the median CRP as the cut-off point. Dialysis adequacy obtained in each group was compared. Finally, a logistic regression model was carried out to determine the variables with the greatest influence.Median CRP was 4.10 mg/L (q25-q75: 1.67-10) and mean Kt/V was 1.48 ± 0.308. Kt/V was lower in the patients included in the high inflammation group (p = 0.01). In the multivariate logistic regression, the "high" levels of CRP were directly correlated with the Log INL (p < 0.001) and inversely proportional with serum albumin values (p = 0.014), Kt/V (p = 0.037) and serum iron (p < 0.001).The poorer adequacy in terms of dialysis doses, lower Kt / V values, may contribute to a higher degree of inflammation in chronic hemodialysis patients. 

Inflammation and hemodialysis adequacy: are C-reactive protein levels influenced by the dose of dialysis?

Reply to Comments on the SENefro Consensus Document on Autosomal Dominant Polycystic Kidney Disease.

Hypochloremia has been associated with increased mortality in patients with hypertension, heart failure, sepsis, and chronic kidney disease (CKD). The pathophysiological mechanisms of this finding are not clear. There are no studies describing an association between serum chloride levels (Cl−) and mortality in incident chronic hemodialysis (HD) patients. Retrospective cohort study of the incident population in our chronic outpatient hemodialysis program between January 1, 2016, and January 1, 2021 (N = 374). Survival time was collected in all patients and analyzed using the Kaplan–Meyer method. A multivariate Cox regression model was performed to predict the probability of survival, applying a stepwise procedure. During the median follow-up period of 20 months, 83 patients died. The 5-year overall survival rate for our patients was 45%. Both natremia and chloremia had no significant differences when compared by sex, vascular access, or etiology. There was an inverse correlation between Cl− and interdialytic weight gain (r = −0.15) (p = 0.0038). Patients belonging to the quartile with lower Cl− levels had less probability of survival than patients in the quartile with higher Cl− levels (27% and 68%, respectively, p = 0.019). On the other hand, in the multivariate Cox regression model, variables significantly associated with higher mortality were being older, having higher baseline comorbidity by modified Charlson index, not taking diuretics and having lower albumin and chloride levels. Particularly, higher Cl− levels was independently associated with both lower all-cause mortality (adjusted hazard ratio [HR] = 0.84; 95% confidence interval [CI], 0.77–0.92; p = 0.0001) and cardiovascular mortality (HR 0.9; 95% CI, 0.83–0.97; p < 0.0057). Lower Cl− levels were associated with higher all-cause and cardiovascular mortality in incident patients on chronic hemodialysis in our health area. 

José Carlos Rodríguez-Pérez

Papers

Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.

Synergy of sodium thiosulphate treatment and expanded hemodialysis in the management of calciphylaxis? A case report.

Inflammation and hemodialysis adequacy: are C-reactive protein levels influenced by the dose of dialysis?

Reply to Comments on the SENefro Consensus Document on Autosomal Dominant Polycystic Kidney Disease.

Serum chloride as a marker of cardiovascular and all-cause mortality in chronic hemodialysis patients: 5-year follow-up study