BACKGROUND: Creating induced pluripotent stem cells (iPSCs) from somatic cells of patients with genetic diseases offers a pathway to generate disease-specific iPSCs carrying genetic markers. Differentiating these iPSCs into renal tubular cells can aid in understanding the pathophysiology of rare inherited renal tubular diseases through cellular experiments.
METHODS: Two Japanese patients with Pseudohypoparathyroidism (PHP), a 49-year-old woman and a 71-year-old man, were studied. iPSC-derived tubular cells were established from their peripheral blood mononuclear cells (PBMCs). We examined changes in intracellular and extracellular cyclic adenosine monophosphate (cAMP) levels in these cells in response to parathyroid hormone (PTH) stimulation.
RESULTS: Renal tubular cells, differentiated from iPSCs of a healthy control (648A1), showed a PTH-dependent increase in both intracellular and extracellular cAMP levels. However, the renal tubular cells derived from the PHP patients\' iPSCs showed inconsistent changes in cAMP levels upon PTH exposure.
CONCLUSIONS: We successfully created disease-specific iPSCs from PHP patients\' PBMCs, differentiated them into tubular cells, and replicated the distinctive response of the disease to PTH in vitro. This approach could enhance our understanding of the pathophysiology of inherited renal tubular diseases and contribute to developing effective treatments.

BACKGROUND: The senescence of renal tubular epithelial cells (RTECs) is crucial in the progression of diabetic kidney disease (DKD). Accumulating evidence suggests a close association between insufficient mitophagy and RTEC senescence. Yeast mitochondrial escape 1-like 1 (YME1L), an inner mitochondrial membrane metalloprotease, maintains mitochondrial integrity. Its functions in DKD remain unclear. Here, we investigated whether YME1L can prevent the progression of DKD by regulating mitophagy and cellular senescence.
METHODS: We analyzed YME1L expression in renal tubules of DKD patients and mice, explored transcriptomic changes associated with YME1L overexpression in RTECs, and assessed its impact on RTEC senescence and renal dysfunction using an HFD/STZ-induced DKD mouse model. Tubule-specific overexpression of YME1L was achieved through the use of recombinant adeno-associated virus 2/9 (rAAV 2/9). We conducted both in vivo and in vitro experiments to evaluate the effects of YME1L overexpression on mitophagy and mitochondrial function. Furthermore, we performed LC-MS/MS analysis to identify potential protein interactions involving YME1L and elucidate the underlying mechanisms.
RESULTS: Our findings revealed a significant decrease in YME1L expression in the renal tubules of DKD patients and mice. However, tubule-specific overexpression of YME1L significantly alleviated RTEC senescence and renal dysfunction in the HFD/STZ-induced DKD mouse model. Moreover, YME1L overexpression exhibited positive effects on enhancing mitophagy and improving mitochondrial function both in vivo and in vitro. Mechanistically, our LC-MS/MS analysis uncovered a crucial mitophagy receptor, BCL2-like 13 (BCL2L13), as an interacting partner of YME1L. Furthermore, YME1L was found to promote the phosphorylation of BCL2L13, highlighting its role in regulating mitophagy.
CONCLUSIONS: This study provides compelling evidence that YME1L plays a critical role in protecting RTECs from cellular senescence and impeding the progression of DKD. Overexpression of YME1L demonstrated significant therapeutic potential by ameliorating both RTEC senescence and renal dysfunction in the DKD mice. Moreover, our findings indicate that YME1L enhances mitophagy and improves mitochondrial function, potentially through its interaction with BCL2L13 and subsequent phosphorylation. These novel insights into the protective mechanisms of YME1L offer a promising strategy for developing therapies targeting DKD.

Even during physiologic aging, the kidney experiences a loss of mass and a progressive functional decline. This is clinically relevant as it leads to an increased risk of acute and chronic kidney disease. The kidney tubular system plays an important role in the underlying aging process, but the involved cellular mechanisms remain largely elusive.
Kidneys of 3-, 12- and 24-month-old male C57BL/6J mice were used for RNA sequencing, histological examination, immunostaining and RNA-in-situ-hybridization. Single cell RNA sequencing data of differentially aged murine and human kidneys was analyzed to identify age-dependent expression patterns in tubular epithelial cells. Senescent and non-senescent primary tubular epithelial cells from mouse kidney were used for in vitro experiments.
During normal kidney aging, tubular cells adopt an inflammatory phenotype, characterized by the expression of MHC class II related genes. In our analysis of bulk and single cell transcriptional data we found that subsets of tubular cells show an age-related expression of Cd74, H2-Eb1 and H2-Ab1 in mice and CD74, HLA-DQB1 and HLADRB1 in humans. Expression of MHC class II related genes was associated with a phenotype of tubular cell senescence, and the selective elimination of senescent cells reversed the phenotype. Exposure to the Cd74 ligand MIF promoted a prosenescent phenotype in tubular cell cultures.
Together, these data suggest that during normal renal aging tubular cells activate a program of \'tubuloinflammaging\', which might contribute to age-related phenotypical changes and to increased disease susceptibility.

Mitochondrial quality control (MQC) plays a critical role in the progression of tubulointerstitial injury in diabetic kidney disease (DKD). The mitochondrial unfolded protein response (UPRmt), which is an important MQC process, is activated to maintain mitochondrial protein homeostasis in response to mitochondrial stress. Activating transcription factor 5 (ATF5) is critical in the mammalian UPRmt via mitochondria-nuclear translocation. However, the role of ATF5 and UPRmt in tubular injury under DKD conditions is unknown.
ATF5 and UPRmt-related proteins including heat shock protein 60 (HSP60) and Lon peptidase 1 (LONP1), in DKD patients and db/db mice were examined by immunohistochemistry (IHC) and western blot analysis. Eight-week-old db/db mice were injected with ATF5-shRNA lentiviruses via the tail vein, and a negative lentivirus was used as a control. The mice were euthanized at 12 weeks, and dihydroethidium (DHE) and TdT-mediated dUTP nick end labeling (TUNEL) assays were performed to evaluate reactive oxygen species (ROS) production and apoptosis in kidney sections, respectively. In vitro, ATF5-siRNA, ATF5 overexpression plasmids or HSP60-siRNA were transfected into HK-2 cells to evaluate the effect of ATF5 and HSP60 on tubular injury under ambient hyperglycemic conditions. Mitochondrial superoxide (MitoSOX) staining was used to gauge mitochondrial oxidative stress levels, and the early stage of cell apoptosis was examined by Annexin V-FITC kits.
Increased ATF5, HSP60 and LONP1 expression was observed in the kidney tissue of DKD patients and db/db mice and was tightly correlated with tubular damage. The inhibition of HSP60 and LONP1, improvements in serum creatinine, tubulointerstitial fibrosis and apoptosis were observed in db/db mice treated with lentiviruses carrying ATF5 shRNA. In vitro, the expression of ATF5 was increased in HK-2 cells exposed to high glucose (HG) in a time-dependent manner, which was accompanied by the overexpression of HSP60, fibronectin (FN) and cleaved-caspase3 (C-CAS3). ATF5-siRNA transfection inhibited the expression of HSP60 and LONP1, which was accompanied by reduced oxidative stress and apoptosis in HK-2 cells exposed to sustained exogenous high glucose. ATF5 overexpression exacerbated these impairments. HSP60-siRNA transfection blocked the effect of ATF5 on HK-2 cells exposed to continuous HG treatment. Interestingly, ATF5 inhibition exacerbated mitochondrial ROS levels and apoptosis in HK-2 cells in the early period of HG intervention (6 h).
ATF5 could exert a protective effect in a very early stage but promoted tubulointerstitial injury by regulating HSP60 and the UPRmt pathway under DKD conditions, providing a potential target for the prevention of DKD progression.

Kidney is one of the most important organs in maintaining the normal life activities. With the high abundance of mitochondria, renal tubular cell plays the vital role in functioning in the reabsorption and secretion of kidney. Reports have shown that mitochondrial dysfunction is of great importance to renal tubular cell senescence and subsequent kidney ageing. However, the underlying mechanisms are not elucidated. Cannabinoid receptor 2 is one of the two receptors responsible for the activation of endocannabinoid system. CB2 is primarily upregulated in renal tubular cells in chronic kidney diseases and mediates fibrogenesis. However, the role of CB2 in tubular mitochondrial dysfunction and kidney ageing has not been clarified. In this study, we found that CB2 was upregulated in kidneys in 24-month-old mice and d-galactose (d-gal)-induced accelerated ageing mice, accompanied by the decrease in mitochondrial mass. Furthermore, gene deletion of CB2 in d-gal-treated mice could greatly inhibit the activation of β-catenin signalling and restore the mitochondrial integrity and Adenosine triphosphate (ATP) production. In CB2 knockout mice, renal tubular cell senescence and kidney fibrosis were also significantly inhibited. CB2 overexpression or activation by the agonist AM1241 could sufficiently induce the decrease in PGC-1α and a variety of mitochondria-related proteins and trigger cellular senescence in cultured human renal proximal tubular cells. CB2-activated mitochondrial dysfunction and cellular senescence could be blocked by ICG-001, a blocker for β-catenin signalling. These results show CB2 plays a central role in renal tubular mitochondrial dysfunction and kidney ageing. The intrinsic mechanism may be related to its activation in β-catenin signalling.

[This corrects the article DOI: 10.3389/fcell.2020.576988.].

The AngioJet technique combines localized thrombolysis and percutaneous mechanical thrombectomy (PMT). However, PMT may cause acute kidney injury (AKI), which has been ascribed to severe mechanical haemolysis, although no renal biopsies have been reported. We now report the first renal biopsy in a patient with AKI following PMT. There is histological evidence of haemoglobin (Hb)-induced tubular injury and podocyte stress characterized by intracellular Hb and staining for ferritin and hemo-oxygenase-1, suggestive of an adaptive response to oxidative stress. This confirms that Hb is involved in kidney cell injury and supports the existence of several different kidney cellular targets.

Bixin, a natural carotenoid extracted from the seeds of Bixa orellana, has antioxidant and anti-inflammation effects. However, the pharmacological effects and underlying mechanisms of bixin in kidney interstitial fibrosis remain unknown. Partial epithelial-to-mesenchymal transition (EMT) of tubular cells has been linked to renal interstitial fibrosis. Here, we found that in the unilateral ureteral obstruction model, bixin administration could ameliorate kidney interstitial fibrosis. The expression of signal transducer and activator of transcription 6 (STAT6) was dramatically increased in renal tubular cells. Bixin treatment inhibited STAT6 induction. The activation of STAT6 signaling was essential for transforming growth factor β1, fibrotic markers, and EMT-related protein expression in HK2 cells, which was confirmed by using the Stat6-/- mice. Ubiquitination, but not the acetylation level of STAT6, was induced by bixin treatment and promoted the suppression of phosphorylation and stability of STAT6. P62-dependent autophagy might be involved in this process. The study demonstrated that bixin can be exploited therapeutically to alleviate renal interstitial fibrosis by targeting STAT6 signaling deactivation.

Tubulointerstitial inflammation is crucial for the progression of diabetic nephropathy (DN), and tubular cells act as a driving force in the inflammatory cascade. Emerging data suggested that tacrolimus (TAC) ameliorates podocyte injury and macrophage infiltration in streptozotocin (STZ) mice. However, the effect of TAC on tubulointerstitial inflammation remains unknown. We found that albuminuria and tubulointerstitial damage improved in db/db mice treated with TAC. Macrophage infiltration and expression of IL-6, TNF-α, fibronectin, collagen 1 and cleaved caspase 3 were inhibited as well. In addition, the expression of nuclear factor of activated T cell 1 (NFATc1) and transient receptor potential channel 6 (TRPC6) was up-regulated in the kidneys of DN patients and correlated with tubular injury and inflammation. The expression of NFATc1 and TRPC6 also increased in the kidneys of db/db mice and HK-2 cells with high glucose (HG), while TAC inhibited these effects. HG-induced inflammatory markers and apoptosis were reversed by TAC and NFATc1 siRNA in HK-2 cells, which was abolished by TRPC6 plasmid. Furthermore, HG-induced TRPC6 expression was inhibited by NFATc1 siRNA, while NFATc1 nuclear translocation was inhibited by TAC, but was restored by TRPC6 plasmid in HK-2 cells under HG conditions. These findings suggest that TAC ameliorates tubulointerstitial inflammation in DN through NFATc1/TRPC6 feedback loop.

Premature senescence of renal tubular epithelial cell (RTEC), which is involved in kidney fibrosis, is a key event in the progression of diabetic nephropathy. However, the underlying mechanism remains unclear. Here we investigated the role and mechanism of decoy receptor 2 (DcR2) in kidney fibrosis and the senescent phenotype of RTEC. DcR2 was specifically expressed in senescent RTEC and associated with kidney fibrosis in patients with diabetic nephropathy and mice with streptozotocin-induced with diabetic nephropathy. Knockdown of DcR2 decreased the expression of α-smooth muscle actin, collagen I, fibronectin and serum creatinine levels in streptozotocin-induced mice. DcR2 knockdown also inhibited the expression of senescent markers p16, p21, senescence-associated beta-galactosidase and senescence-associated heterochromatic foci and promoted the secretion of a senescence-associated secretory phenotype including IL-6, TGF-β1, and matrix metalloproteinase 2 in vitro and in vivo. However, DcR2 overexpression showed the opposite effects. Quantitative proteomics and validation studies revealed that DcR2 interacted with peroxiredoxin 1 (PRDX1), which regulated the cell cycle and senescence. Knockdown of PRDX1 upregulated p16 and cyclin D1 while downregulating cyclin-dependent kinase 6 expression in vitro, resulting in RTEC senescence. Furthermore, PRDX1 knockdown promoted DcR2-induced p16, cyclin D1, IL-6, and TGF-β1 expression, whereas PRDX1 overexpression led to the opposite results. Subsequently, DcR2 regulated PRDX1 phosphorylation, which could be inhibited by the specific tyrosine kinase inhibitor genistein. Thus, DcR2 mediated the senescent phenotype of RTEC and kidney fibrosis by interacting with PRDX1. Hence, DcR2 may act as a potential therapeutic target for the amelioration of diabetic nephropathy progression.