Three-dimensional spheroid culture induces apical-basal polarity and the original characteristics of immortalized human renal proximal tubule epithelial cells

Advanced in vitro evaluation of drug-induced kidney injury using microphysiological systems in drug discovery and development

Drug-induced kidney injury (DIKI) is a major cause of acute kidney injury (AKI). Given concerns about animal welfare and the need for more accurate prediction of human events, there is an urgent need to develop an in vitro evaluation method for DIKI using human cells. Renal proximal tubular epithelial cells (RPTECs) are the main targets of DIKI in drug discovery and development because of their abundant expression of drug transporters that contribute to renal-specific drug distribution. In general, physiological kidney function is significantly reduced in primary cell monolayer culture systems. However, with recent advances in cell engineering and regenerative medicine, human kidney-derived cell culture systems, with higher kidney function compared to conventional systems, have been established. For example, three-dimensional cultured RPTECs show enhanced expression of drug transporters and higher predictive performance than monolayer culture systems. The use of organs-on-a-chip with liver and kidney co-cultures also allows the detection of drug metabolite-induced nephrotoxicity. Kidney organoids differentiated from induced pluripotent stem cells (iPS) have also been established. In this review, we introduce a recently established renal cell culture system that includes a microphysiological system, and review the in vitro methods used to evaluate DIKI in RPTECs.

Opportunities for microphysiological systems from the view of Japanese industries

Regulatory authorities and pharmaceutical companies in Europe and the United States have paid attention to microphysiological systems (MPS), and various consortia and academic societies have been established. They are actively working toward their implementation under individual company or regulatory acceptance. In Japan, some AMED projects, academic societies, and consortia have also been established and activities have begun. This article focuses on domestic and international trends regarding MPS, especially on Japanese industries related to MPS, and describes the current status, challenges, and prospects of Japanese pharmaceutical companies, CROs, Food company, and MPS-related product development companies including the results of a survey conducted by CSAHi-MPS, an industrial MPS consortium in Japan.

SARS-CoV-2 Spike Protein Amplifies the Immunogenicity of Healthy Renal Epithelium in the Presence of Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most common form of kidney cancer, known for its immune evasion and resistance to chemotherapy. Evidence indicates that the SARS-CoV-2 virus may worsen outcomes for RCC patients, as well as patients with diminished renal function. Evidence suggests that the SARS-CoV-2 virus may exacerbate outcomes in RCC patients and those with impaired renal function. This study explored the unidirectional effects of RCC cells and the SARS-CoV-2 spike protein (S protein) on human renal proximal tubule epithelial cells (RPTECs) using a microphysiological approach. We co-cultured RCC cells (Caki-1) with RPTEC and exposed them to the SARS-CoV-2 S protein under dynamic 3D conditions. The impact on metabolic activity, gene expression, immune secretions, and S protein internalization was evaluated. The SARS-CoV-2 S protein was internalized by RPTEC but poorly interacted with RCC cells. RPTECs exposed to RCC cells and the S protein exhibited upregulated expression of genes involved in immunogenic pathways, particularly those related to antigen processing and presentation via the major histocompatibility complex I (MHCI). Additionally, increased TNF-α secretion suggested a pro-inflammatory response. Metabolic shifts toward glycolysis were observed in RCC co-culture, while the presence of the S protein led to minor changes. The presence of RCC cells amplified the immune-modulatory effects of the SARS-CoV-2 S protein on the renal epithelium, potentially exacerbating renal inflammation and fostering tumor-supportive conditions. These findings suggest that COVID-19 infections can impact renal function in the presence of kidney cancer.

TRPML1 agonist ML-SA5 mitigates uranium-induced nephrotoxicity via promoting lysosomal exocytosis

Uranium (U) released from U mining and spent nuclear fuel reprocessing in the nuclear industry, nuclear accidents and military activities as a primary environmental pollutant (e.g., drinking water pollution) is a threat to human health. Kidney is one of the main target organs for U accumulation, leading to nephrotoxicity mainly associated with the injuries in proximal tubular epithelial cells (PTECs). Transient receptor potential mucolipin 1 (TRPML1) is a novel therapeutic target for nephrotoxicity caused by acute or chronic U poisoning. We herein investigate the therapeutic efficacy of ML-SA5, a small molecule agonist of TRPML1, in U-induced nephrotoxicity in acute U intoxicated mice. We demonstrate that delayed treatment with ML-SA5 enhances U clearance from the kidneys via urine excretion by activating lysosomal exocytosis, and thereby attenuates U-induced kidney dysfunction and cell death/apoptosis of renal PTECs in acute U intoxicated mice. In addition, ML-SA5 promotes the nuclear translocation of transcription factor EB (TFEB) in renal PTECs in acute U intoxicated mice. Mechanistically, ML-SA5 triggers the TRPML1-mediated lysosomal calcium release and consequently induces TFEB activation in U-loaded renal PTECs-derived HK-2 cells. Moreover, knockdown of TRPML1 or TFEB abolishes the effects of ML-SA5 on the removal of intracellular U and reduction of the cellular injury/death in U-loaded HK-2 cells. Our findings indicate that pharmacological activation of TRPML1 is a promising therapeutic approach for the delayed treatment of U-induced nephrotoxicity via the activation of the positive feedback loop of TRPML1 and TFEB and consequent the induction of lysosomal exocytosis.

Kynurenine 3-monooxygenase limits de novo NAD+ synthesis through dietary tryptophan in renal proximal tubule epithelial cell models

Nicotinamide adenine dinucleotide (NAD+) is a pivotal coenzyme, essential for cellular reactions, metabolism, and mitochondrial function. Depletion of kidney NAD+ levels and reduced de novo NAD+ synthesis through the tryptophan-kynurenine pathway are linked to acute kidney injury (AKI), whereas augmenting NAD+ shows promise in reducing AKI. We investigated de novo NAD+ biosynthesis using in vitro, ex vivo, and in vivo models to understand its role in AKI. Two-dimensional (2-D) cultures of human primary renal proximal tubule epithelial cells (RPTECs) and HK-2 cells showed limited de novo NAD+ synthesis, likely due to low pathway enzyme gene expression. Using three-dimensional (3-D) spheroid culture model improved the expression of tubular-specific markers and enzymes involved in de novo NAD+ synthesis. However, de novo NAD+ synthesis remained elusive in the 3-D spheroid culture, regardless of injury conditions. Further investigation revealed that 3-D cultured cells could not metabolize tryptophan (Trp) beyond kynurenine (KYN). Intriguingly, supplementation of 3-hydroxyanthranilic acid into RPTEC spheroids was readily incorporated into NAD+. In a human precision-cut kidney slice (PCKS) ex vivo model, de novo NAD+ synthesis was limited due to substantially downregulated kynurenine 3-monooxygenase (KMO), which is responsible for KYN to 3-hydroxykynurenine conversion. KMO overexpression in RPTEC 3-D spheroids successfully reinstated de novo NAD+ synthesis from Trp. In addition, in vivo study demonstrated that de novo NAD+ synthesis is intact in the kidney of the healthy adult mice. Our findings highlight disrupted tryptophan-kynurenine NAD+ synthesis in in vitro cellular models and an ex vivo kidney model, primarily attributed to KMO downregulation.NEW & NOTEWORTHY Nicotinamide adenine dinucleotide (NAD+) is essential in regulating mitochondrial function. Reduced NAD+ synthesis through the de novo pathway is associated with acute kidney injury (AKI). Our study reveals a disruption in de novo NAD+ synthesis in proximal tubular models, but not in vivo, attributed to downregulation of enzyme kynurenine 3-monooxygenase (KMO). These findings highlight a crucial role of KMO in governing de novo NAD+ biosynthesis within the kidney, shedding light on potential AKI interventions.

Renogrit attenuates Vancomycin-induced nephrotoxicity in human renal spheroids and in Sprague-Dawley rats by regulating kidney injury biomarkers and creatinine/urea clearance

Vancomycin, is widely used against methicillin-resistant bacterial infections. However, Vancomycin accumulation causes nephrotoxicity which leads to an impairment in the filtration mechanisms of kidney. Traditional herbal medicines hold potential for treatment of drug-induced nephrotoxicity. Herein, we investigated protective properties of plant-based medicine Renogrit against Vancomycin-induced kidney injury. Phytometabolite analysis of Renogrit was performed by UHPLC. Spheroids formed from human proximal tubular cell (HK-2) were used for in vitro evaluation of Vancomycin-induced alterations in cell viability, P-gp functionality, NAG, KIM-1 levels, and mRNA expression of NGAL and MMP-7. The in vivo efficacy of Renogrit against Vancomycin-induced nephrotoxicity was further evaluated in Sprague-Dawley (SD) rats by measurement of BUN, serum creatinine, and their respective clearances. Moreover, eGFR, kidney-to-body weight ratio, GSH/GSSG ratio, KIM-1, NAG levels and mRNA expression of KIM-1 and osteopontin were also analyzed. Changes in histopathology of kidney and hematological parameters were also observed. Renogrit treatment led to an increase in cell viability, normalization of P-gp functionality, decrease in levels of NAG, KIM-1, and reduction in mRNA expression of NGAL and MMP-7. In Vancomycin-challenged SD rats, Renogrit treatment normalized altered kidney functions, histological, and hematological parameters. Our findings revealed that Renogrit holds a clinico-therapeutic potential for alleviating Vancomycin-associated nephrotoxicity.

Kidney Proximal Tubule GLUT2-More than Meets the Eye

Tubulopathy plays a central role in the pathophysiology of diabetic kidney disease (DKD). Under diabetic conditions, the kidney proximal tubule cells (KPTCs) are exposed to an extensive amount of nutrients, most notably glucose; these nutrients deteriorate KPTCs function and promote the development and progression of DKD. Recently, the facilitative glucose transporter 2 (GLUT2) in KPTCs has emerged as a central regulator in the pathogenesis of DKD. This has been demonstrated by identifying its specific role in enhancing glucose reabsorption and glucotoxicity, and by deciphering its effect in regulating the expression of the sodium-glucose transporter 2 (SGLT2) in KPTCs. Moreover, reduction/deletion of KPTC-GLUT2 has been recently found to ameliorate DKD, raising the plausible idea of considering it as a therapeutic target against DKD. However, the underlying molecular mechanisms by which GLUT2 exerts its deleterious effects in KPTCs remain vague. Herein, we review the current findings on the proximal tubule GLUT2 biology and function under physiologic conditions, and its involvement in the pathophysiology of DKD. Furthermore, we shed new light on its cellular regulation during diabetic conditions.

The sugar daddy: the role of the renal proximal tubule in glucose homeostasis

Renal blood flow represents >20% of total cardiac output and with this comes the great responsibility of maintaining homeostasis through the intricate regulation of solute handling. Through the processes of filtration, reabsorption, and secretion, the kidneys ensure that solutes and other small molecules are either returned to circulation, catabolized within renal epithelial cells, or excreted through the process of urination. Although this occurs throughout the renal nephron, one segment is tasked with the bulk of solute reabsorption-the proximal tubule. Among others, the renal proximal tubule is entirely responsible for the reabsorption of glucose, a critical source of energy that fuels the body. In addition, it is the only other site of gluconeogenesis outside of the liver. When these processes go awry, pathophysiological conditions such as diabetes and acidosis result. In this review, we highlight the recent advances made in understanding these processes that occur within the renal proximal tubule. We focus on the physiological mechanisms at play regarding glucose reabsorption and glucose metabolism, emphasize the conditions that occur under diseased states, and explore the emerging class of therapeutics that are responsible for restoring homeostasis.

Tissue Culture Models of AKI: From Tubule Cells to Human Kidney Organoids

AKI affects approximately 13.3 million people around the world each year, causing CKD and/or mortality. The mammalian kidney cannot generate new nephrons after postnatal renal damage and regenerative therapies for AKI are not available. Human kidney tissue culture systems can complement animal models of AKI and/or address some of their limitations. Donor-derived somatic cells, such as renal tubule epithelial cells or cell lines (RPTEC/hTERT, ciPTEC, HK-2, Nki-2, and CIHP-1), have been used for decades to permit drug toxicity screening and studies into potential AKI mechanisms. However, tubule cell lines do not fully recapitulate tubular epithelial cell properties in situ when grown under classic tissue culture conditions. Improving tissue culture models of AKI would increase our understanding of the mechanisms, leading to new therapeutics. Human pluripotent stem cells (hPSCs) can be differentiated into kidney organoids and various renal cell types. Injury to human kidney organoids results in renal cell-type crosstalk and upregulation of kidney injury biomarkers that are difficult to induce in primary tubule cell cultures. However, current protocols produce kidney organoids that are not mature and contain off-target cell types. Promising bioengineering techniques, such as bioprinting and "kidney-on-a-chip" methods, as applied to kidney nephrotoxicity modeling advantages and limitations are discussed. This review explores the mechanisms and detection of AKI in tissue culture, with an emphasis on bioengineered approaches such as human kidney organoid models.

Establishment and characterization of organoids from a patient with adenomyoepithelioma of the breast

Adenomyoepithelioma (AME) of the breast is a rare tumor that is composed of proliferating epithelial and myoepithelial cells. The pathogenesis of AME remains unclear, and no breast cancer cells have been identified in such tumor tissues. In this study, we established patient-derived breast cancer organoids from the surgical tumor samples of an elderly Chinese woman with an AME of the breast. Our findings confirmed the successful establishment of organoids from an AME of the breast of this patient. A short tandem repeat analysis revealed that the DNA signature of the AME of the breast organoids matched the DNA signature of the original tumor specimen. Moreover, diameter assay confirmed that the organoids from the breast AME showed sensitivity to paclitaxel and doxorubicin treatments, which was similar to, but lesser than that of primary culture cells. In conclusion, we established an efficient 3-dimensional breast cancer organoid culture platform from an AME of the breast. This platform can be effectively used for exploring clinicopathological and genomic characteristics of AME of the breast to identify possible treatments and increase awareness about this disease entity.