Actin phosphorylation correlates with actin sequestration in ATP-depleted rabbit renal proximal tubules

Objective: To demonstrate the relation sh ip between actin phosphorylation and actin sequestration in ATP-depleted rabbi t renal proximal tubules. Methods: Using two-dimensional electr ophoreses and Western blotting to analyze the phosphorylation state of the seque stered actin in rabbit renal proximal tubules. Results: The anal ytical result of the sequestered actin indicated that nearly half of the actin w as phosphorylated on serine residue(s). Conclusion: Result sugge sted a close correlation between actin sequestration and actin phosphorylation i n ATP-depleted rabbit renal proximal tubules.

Different modes of renal proximal tubule regeneration in health and disease

Tissues are equipped with reasonable strategies for re-pair and regeneration and the renal proximal tubule （PT）is no exception. New information has become availableon the mode of PT regeneration in mammals. Unlikethe intestinal epithelium with a high rate of turnovermaintained by the stem cell system, the kidney has lowturnover under normal physiological conditions. The PTseems to be maintained physiologically by hyperplasia,a regenerating system with self-renewal of mature tu-bular cells. This mode of regeneration is advantageousfor effective replenishment of randomly isolated andeliminated tubular cells by self-renewal of adjacentcells. On the other hand, it has been suggested thatdedifferentiation of mature tubular cells plays a role inregeneration after acute kidney injury. Recent studiesemploying genetic labeling and DNA-labeling tech-niques have confrmed that the proliferation of preex-isting injured mature tubular cells contributes mainlyto PT regeneration in ischemic reperfusion injury. Thismode of regeneration is beneficial with regard to therapid reparation of focally injured tubules often inducedby ischemic reperfusion injury. What happens, howeverwhen the PT is homogeneously injured with almost noremaining surviving cells？ Is the PT equipped with another backup regeneration system, e.g., the stem cell system？ Is it possible that certain types of renal injuries evoke a stem cell response whereas others do not？ This review focuses on all three possible modes of tis-sue regeneration （compensatory hyperplasia, dediffer-entiation and stem cell system） in mammals and their involvement in PT regeneration in health and disease.

Species differences in regulation of renal proximal tubule transport by certain molecules

Renal proximal tubules （PTs） play important roles in the regulation of acid/base, plasma volume and blood pressure. Recent studies suggest that there are substantial species differences in the regulation of PT transport. For example, thiazolidinediones （TZDs） are widely used for the treatment of type 2 diabetes mellitus, but the use of TZDs is associated with fluid overload. In addition to the transcriptional enhancement of sodium transport in distal nephrons, TZDs rapidly stimulate PT sodium transport via a non-genomic mechanism depending onperoxisome proliferator activated receptor g/Src/epidermal growth factor receptor （EGFR）/MEK/ERK. In mouse PTs, however, TZDs fail to stimulate PT transport probably due to constitutive activation of Src/EGFR/ERK pathway. This unique activation of Src/ERK may also affect the effect of high concentrations of insulin on mouse PT transport. On the other hand, the effect of angiotensin Ⅱ （Ang Ⅱ） on PT transport is known to be biphasic in rabbits, rats, and mice. However, Ang Ⅱ induces a concentration-dependent, monophasic transport stimulation in human PTs. The contrasting responses to nitric oxide/guanosine 3’,5’-cyclic monophosphate pathway may largely explain these different effects of Ang Ⅱ on PT transport. In this review, we focus on the recent fndings on the species differences in the regulation of PT transport, which may help understand the species-specific mechanisms underlying edema formation and/or hypertension occurrence.

F-Actin Distribution Changes Provoked by Acetaminophen in the Proximal Tubule in Kidney of Adult Male Rat

Acetaminophen is a drug used to treat many conditions as headache, muscle aches, arthritis, backache, toothache, and fever between others, but collateral effects of this drug are not well known yet. Here is tested its effect on proximal tubule epithelium. Acetaminophen (APAP) at doses of 200, 500, 1000 and 1500 mg/Kg i.p. caused cell damage and changes in F-actin distribution in the proximal tubule of male Wistar rats. After 48 hours of treatment, the proximal tubule epithelium showed tumefaction and necrosis. Dose of 200 mg/kg decreased the F-actin and was observed a structure in patches in the basal cytoplasm of epithelial cells of the proximal tubule. This effect was increased depending on the administered dose. Dose of 1000 mg/kg produced the highest histological damage and changes in the actin cytoskeleton. Results of this study suggested that nephrotoxic damage produced by high doses of APAP included breakdown of cytoskeleton in proximal tubule epithelium.

Long Term Culture of Human Kidney Proximal Tubule Epithelial Cells Maintains Lineage Functions and Serves as an Ex vivo Model for Coronavirus Associated Kidney Injury

The mechanism of how SARS-CoV-2 causes severe multi-organ failure is largely unknown. Acute kidney injury(AKI) is one of the frequent organ damage in severe COVID-19 patients. Previous studies have shown that human renal tubule cells could be the potential host cells targeted by SARS-CoV-2. Traditional cancer cell lines or immortalized cell lines are genetically and phenotypically different from host cells. Animal models are widely used, but often fail to reflect a physiological and pathogenic status because of species tropisms. There is an unmet need for normal human epithelial cells for disease modeling. In this study, we successfully established long term cultures of normal human kidney proximal tubule epithelial cells(KPTECs) in 2 D and 3 D culture systems using conditional reprogramming(CR) and organoids techniques.These cells had the ability to differentiate and repair DNA damage, and showed no transforming property. Importantly, the CR KPTECs maintained lineage function with expression of specific transporters(SLC34 A3 and cubilin). They also expressed angiotensin-converting enzyme 2(ACE2), a receptor for SARS-CoV and SARS-CoV-2. In contrast, cancer cell line did not express endogenous SLC34 A3, cubilin and ACE2. Very interestingly, ACE2 expression was around twofold higher in 3 D organoids culture compared to that in 2 D CR culture condition. Pseudovirion assays demonstrated that SARS-CoV spike(S) protein was able to enter CR cells with luciferase reporter. This integrated 2 D CR and 3 D organoid cultures provide a physiological ex vivo model to study kidney functions, innate immune response of kidney cells to viruses, and a novel platform for drug discovery and safety evaluation.

ANGIOTENSIN Ⅱ-INDUCED CELLULAR HYPERTROPHY: POTENTIAL ROLE OF THE PROTEOLYTIC ACTIVITY IN CULTURED PROXIMAL TUBULE CELLS (LLC-PK1)

In a number of renal disease tubular epithelial cells often display hypertrophy rather than hyperplasia. This hypertrophy, characterized by an increase in protein conten and cell size, as well as an accumulation of extracellular matrix, is a key process which may lead subsequently to tubulointerstitial fibrosis and end-stage renal failure.

Regulatory roles of nitric oxide and angiotensin Ⅱ on renal tubular transport

Renal tubules regulate blood pressure and humoral homeostasis. Mediators that play a significant role in regulating the transport of solutes and water include angiotensin Ⅱ （AngⅡ） and nitric oxide （NO）. AngⅡcan signifcantly raise blood pressure via effects on the heart, vasculature, and renal tubules. AngⅡ generally stimulates sodium reabsorption by triggering sodium and fuid retention in almost all segments of renal tu-bules. Stimulation of renal proximal tubule （PT） trans-port is thought to be essential for AngⅡ-mediated hy-pertension. However, AngⅡ has a biphasic effect on in vitro PT transport in mice, rats, and rabbits： stimulation at low concentrations and inhibition at high concentra-tions. On the other hand, NO is generally thought to inhibit renal tubular transport. In PTs, NO seems to be involved in the inhibitory effect of AngⅡ. A recent study reports a surprising fnding： AngⅡ has a mono-phasic stimulatory effect on human PT transport. De-tailed analysis of signalling mechanisms indicates that in contrast to other species, the human NO/guanosine 3’,5’-cyclic monophosphate/extracellular signal-regulat-ed kinase pathway seems to mediate this effect of Ang Ⅱ on PT transport. In this review we will discuss recent progress in understanding the effects of AngⅡ and NO on renal tubular transport.

Single-cell RNA sequencing reveals the transcriptomic landscape of kidneys in patients with ischemic acute kidney injury

Background:Ischemic acute kidney injury(AKI)is a common syndrome associated with considerable mortality and healthcare costs.Up to now,the underlying pathogenesis of ischemic AKI remains incompletely understood,and specific strategies for early diagnosis and treatment of ischemic AKI are still lacking.Here,this study aimed to define the transcriptomic landscape of AKI patients through single-cell RNA sequencing(scRNA-seq)analysis in kidneys.Methods:In this study,scRNA-seq technology was applied to kidneys from two ischemic AKI patients,and three human public scRNA-seq datasets were collected as controls.Differentially expressed genes(DEGs)and cell clusters of kidneys were determined.Gene ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway enrichment analysis,as well as the ligand-receptor interaction between cells,were performed.We also validated several DEGs expression in kidneys from human ischemic AKI and ischemia/reperfusion(I/R)injury induced AKI mice through immunohistochemistry staining.Results:15 distinct cell clusters were determined in kidney from subjects of ischemic AKI and control.The injured proximal tubules(PT)displayed a proapoptotic and proinflammatory phenotype.PT cells of ischemic AKI had up-regulation of novel pro-apoptotic genes including USP47,RASSF4,EBAG9,IER3,SASH1,SEPTIN7,and NUB1,which have not been reported in ischemic AKI previously.Several hub genes were validated in kidneys from human AKI and renal I/R injury mice,respectively.Furthermore,PT highly expressed DEGs enriched in endoplasmic reticulum stress,autophagy,and retinoic acid-inducible gene I(RIG-I)signaling.DEGs overexpressed in other tubular cells were primarily enriched in nucleotide-binding and oligomerization domain(NOD)-like receptor signaling,estrogen signaling,interleukin(IL)-12 signaling,and IL-17 signaling.Overexpressed genes in kidney-resident immune cells including macrophages,natural killer T(NKT)cells,monocytes,and dendritic cells were associated with leukocyte activation,chemotaxis,cell adhesion,and complement activation.In addition,the ligand-receptor interactions analysis revealed prominent communications between macrophages and monocytes with other cells in the process of ischemic AKI.Conclusion:Together,this study reveals distinct cell-specific transcriptomic atlas of kidney in ischemic AKI patients,altered signaling pathways,and potential cell-cell crosstalk in the development of AKI.These data reveal new insights into the pathogenesis and potential therapeutic strategies in ischemic AKI.

Inherited Fanconi syndrome

Background Fanconi-Debré-de Toni syndrome(also known as Fanconi renotubular syndrome,or FRST)profoundly increased the understanding of the functions of the proximal convoluted tubule(PCT)and provided important insights into the pathophysiology of several kidney diseases and drug toxicities.Data sources We searched Pubmed and Scopus databases to find relevant articles about FRST.This review article focuses on the physiology of the PCT,as well as on the physiopathology of FRST in children,its diagnosis,and treatment.Results FRST encompasses a wide variety of inherited and acquired PCT alterations that lead to impairment of PCT reab-sorption.In children,FRST often presents as a secondary feature of systemic disorders that impair energy supply,such as Lowe's syndrome,Dent's disease,cystinosis,hereditary fructose intolerance,galactosemia,tyrosinemia,Alport syndrome,and Wilson's disease.Although rare,congenital causes of FRST greatly impact the morbidity and mortality of patients and impose diagnostic challenges.Furthermore,its treatment is diverse and considers the ability of the clinician to identify the correct etiology of the disease.Conclusion The early diagnosis and treatment of pediatric patients with FRST improve the prognosis and the quality of life.