Role of Calbindin-D28k in Diabetes-Associated Advanced Glycation End-Products-Induced Renal Proximal Tubule Cell Injury

Methylglyoxal-derived hydroimidazolone-1/RAGE axis induces renal oxidative stress and renal fibrosis in vitro and in vivo

Advanced glycation end products (AGEs) are important contributors to the progression of chronic kidney diseases (CKD), including renal fibrosis. Although the relationship between AGEs and renal fibrosis has been well studied, the mechanisms of individual AGE-induced renal injury remain poorly understood. This study investigated the adverse effect of methylglyoxal-derived hydroimidazolone-1 (MG-H1), a methylglyoxal (MG)-derived AGE generated by the glycation of MG and arginine residues, on kidney damage. We aimed to elucidate the molecular mechanisms of MG-H1-mediated renal injury and fibrosis, focusing on the receptor for AGEs (RAGE) signaling and its effects on the Wnt/β-catenin pathway, MAPK pathway, and inflammatory responses. Our results suggest that the MG-H1/RAGE axis plays a significant role in the pathogenesis of CKD and its downstream events involving MAPK kinase-related factors and inflammatory factors. MG-H1 treatment modulated the expression of inflammatory cytokines (TNF-α, IL-6, and IL-1β) and MAPK proteins (ERK1/2, JNK, and p38).

LncRNA SNHG14 silencing attenuates the progression of diabetic nephropathy via the miR-30e-5p/SOX4 axis

BACKGROUND

Diabetic nephropathy (DN) is a diabetic complication. LncRNAs are reported to participate in the pathophysiology of DN. Here, the function and mechanism of lncRNA small nucleolar RNA host gene 14 (SNHG14) in DN were explored.

METHODS

Streptozotocin (STZ)-induced DN mouse models and high glucose (HG)-treated human mesangial cells (MCs) were used to detect SNHG14 expression. SNHG14 silencing plasmids were applied to examine the function of SNHG14 on proliferation and fibrosis in HG-treated MCs. Potential targets of SNHG14 were predicted using bioinformatics tools and verified by luciferase reporter, RNA pulldown, and northern blotting assays. The functional role of SNHG14 in DN in vivo was detected by injection with adenoviral vector carrying sh-SNHG14 into DN mice. Serum creatinine, blood urea nitrogen, blood glucose, 24-h proteinuria, relative kidney weight, and renal pathological changes were examined in DN mice.

RESULTS

SNHG14 expression was elevated in the kidneys of DN mice and HG-treated MCs. SNHG14 silencing inhibited proliferation and fibrosis of HG-stimulated MCs. SNHG14 bound to miR-30e-5p to upregulate SOX4 expression. In rescue assays, SOX4 elevation diminished the effects of SNHG14 silencing in HG-treated MCs, and SOX4 silencing reversed the effects of SNHG14 overexpression. In in vivo studies, SNHG14 downregulation significantly ameliorated renal injuries and renal interstitial fibrosis in DN mice.

CONCLUSIONS

SNHG14 silencing attenuates kidney injury in DN mice and reduces proliferation and fibrotic phenotype of HG-stimulated MCs via the miR-30e-5p/SOX4 axis.

Effects of hyperglycemia on the TGF-β pathway in trabecular meshwork cells

BACKGROUND

Hyperglycemia, which can lead to apoptosis, hypertrophy, fibrosis, and induces hyperinflammation in diabetic vascular complications due to oxidative stress. In order to elucidate the potential dual roles and regulatory signal transduction of TGF-β1 and TGF-β2 in human trabecular meshwork cells (HTMCs), we established an oxidative cell model in HTMCs using 5.5, 25, 50, and 100 mM d-glucose-supplemented media and characterized the TGF-β-related oxidative stress pathway.

METHODS

Further analysis was conducted to investigate oxidative damage and protein alterations in the HTMC caused by the signal transduction. This was done through a series of qualitative cell function studies, such as cell viability/apoptosis analysis, intracellular reactive oxygen species (ROS) detection, analysis of calcium release concentration, immunoblot analysis to detect the related protein expression alteration, and analysis of cell fibrosis to study the effect of different severities of hyperglycemia. Also, we illustrated the role of TGF-β1/2 in oxidative stress-induced injury by shRNA-mediated knockdown or stimulation with recombinant human TGF-β1 protein (rhTGF-β1).

RESULTS

Results from the protein expression analysis showed that p-JNK, p-p38, p-AKT, and related SMAD family members were upregulated in HTMCs under hyperglycemia. In the cell functional assays, HTMCs treated with rhTGFβ-1 (1 ng/mL) under hyperglycemic conditions showed higher proliferation rates and lower ROS and calcium levels.

CONCLUSIONS

To summarize, mechanistic analyses in HTMCs showed that hyperglycemia-induced oxidative stress activated TGF-β1 along with its associated pathway.

GENERAL SIGNIFICANCE

While at low concentrations, TGF-β1 protects cells from antioxidation, whereas at high concentrations, it accumulates in the extracellular matrix, causing further HTMC dysfunction.

Yak milk promotes renal calcium reabsorption in mice with osteoporosis via the regulation of TRPV5

The Ca2+-selective epithelial channel TRPV5 plays a significant role in renal calcium reabsorption and improving osteoporosis (OP). In this study, we investigated the mechanisms of yak milk on osteoporosis mice in TRPV5-mediated Ca2+ reabsorption in the kidney. We observed that treatment of OP mice with yak milk reconstructed bone homeostasis demonstrated by increasing the levels of OPG as well as decreasing the levels of TRAP and ALP in serum. Additionally, yak milk reduced the level of parathyroid hormone (PTH) and elevated 1,25-(OH)2D3 and calcitonin (CT), and inhibited the excretion of Ca/Cr and Pi/Cr in OP mice, which explained by regulating hormone levels and thus enhance the renal Ca2+ reabsorption. Further analysis exhibited that yak milk upregulated the expression of TRPV5 protein and mRNA as well as calbindin-D28k in OP mice kidneys. Overall, these outcomes demonstrate that yak milk enhances renal Ca2+ reabsorption through the TRPV5 pathway synergistically with calbindin-D28k, thus ameliorating OP mice. This provides a new perspective for yak milk as a nutritional supplement to prevent osteoporosis.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Isoliquiritigenin ameliorates advanced glycation end-products toxicity on renal proximal tubular epithelial cells

Diabetic nephropathy is a serious chronic complication affecting at least 25% of diabetic patients. Hyperglycemia associated advanced glycation end-products (AGEs) increase tubular epithelial-myofibroblast transdifferentiation (TEMT) and extracellular matrix synthesis and thereby causes renal fibrosis. The chalcone isoliquiritigenin, found in many herbs of Glycyrrhiza family, is known for potential health-promoting effects. However, their effects on AGE-associated renal proximal tubular fibrosis are not known yet. In this study, the effect of isoliquiritigenin on AGE-induced renal proximal tubular fibrosis was determined in cultured HK-2 cell line. The results show that 200 μg/mL of AGE-induced TEMT and the formed myofibroblasts synthesized collagen to increase extracellular matrix formation thereby lead to renal tubular fibrosis. However, treatment with 200 nM of isoliquiritigenin considerably inhibited the TEMT and suppressed the TGFβ/STAT3 mechanism to inhibit collagen secretion. Therefore, isoliquiritigenin effectively suppressed AGE-induced renal tubular fibrosis.

Long Noncoding RNA MEG3-205/Let-7a/MyD88 Axis Promotes Renal Inflammation and Fibrosis in Diabetic Nephropathy

AIM

The aim of this study was to investigate the role and mechanism of long noncoding RNA (lncRNA) maternally expressed gene 3 (MEG3)-205 in renal inflammation and fibrosis in diabetic nephropathy (DN).

MATERIALS AND METHODS

lncRNA microarray profiling was used to examine differentially expressed lncRNAs of kidney tissues in db/db mice compared to db/m mice. Mouse mesangial cells (mMCs) were cultured in vitro with advanced glycation end products (AGEs) via transfection with lncRNA MEG3-205 siRNAs or plasmids. The role of lncRNA MEG3-205 in vivo was examined in db/db mice treated with long-acting lncRNA MEG3-205 siRNA. The interaction between lncRNA MEG3-205 and let-7a was investigated using luciferase assay and RNA immunoprecipitation assay.

RESULTS

lncRNA MEG3-205 was markedly upregulated in renal tissues of db/db mice, DN patients, and AGEs-treated mesangial cells. Overexpression of lncRNA MEG3-205 promoted the secretion of pro-inflammatory cytokines and synthesis of extracellular matrix proteins in mesangial cells. Both lncRNA MEG3-205 and myeloid differentiation primary-response protein 88 (MyD88) could bind to let-7a, and lncRNA MEG3-205 overexpression can significantly rescue the silencing effect of let-7a on MyD88 protein expression in mMCs. Mechanistically, we identified that lncRNA MEG3-205 could act as a competing endogenous RNA by binding with let-7a and thus regulate MyD88. Knockdown of lncRNA MEG3-205 alleviated albuminuria and attenuated renal inflammation and fibrosis in db/db mice.

CONCLUSION

These findings indicated an important role of the lncRNA MEG3-205/let-7a/MyD88 axis in regulating renal inflammation and fibrosis in DN. Targeting lncRNA MEG3-205 might present a promising therapeutic strategy for DN.

Activation of Transcription Factor EB Alleviates Tubular Epithelial Cell Injury via Restoring Lysosomal Homeostasis in Diabetic Nephropathy

Disruption of lysosomal homeostasis contributes to the tubulopathy of diabetic nephropathy; however, its underlying mechanisms remain unclear. Herein, we report that decreased activity of transcription factor EB (TFEB) is responsible for the disturbed lysosome biogenesis and clearance in this pathological process. This was confirmed by the findings that insufficient lysosomal replenishment and damaged lysosomal clearance coincided with TFEB inactivation, which was mediated by mTOR hyperactivation in the renal tubular epithelial cells (TECs) of diabetic nephropathy. Furthermore, either TFEB overexpression or pharmacological activation of TFEB enhanced lysosomal clearance via promoting lysosomal biogenesis and protected TECs by reducing apoptosis in vitro. In addition, pharmacological activation of TFEB attenuated renal tubule injury, apoptosis, and inflammation in db/db mice. In conclusion, diabetes-induced mTOR activation represses TFEB function, thereby perturbing lysosomal homeostasis through impairing lysosomal biogenesis and clearance in TECs. Moreover, TFEB activation protects TECs from diabetic injuries via restoring lysosomal homeostasis.

AGE/RAGE in diabetic kidney disease and ageing kidney

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease that inevitably progress to end-stage kidney disease. Intervention strategies such as blood glucose control is effective for preventing DKD, but many patients with DKD still reach end-stage kidney disease. Although comprehensive mechanisms shed light on the progression of DKD, the most compelling evidence has highlighted that hyperglycemia-related advanced glycation end products (AGEs) formation plays a central role in the pathogenesis of DKD. Pathologically, accumulation of AGEs-mediated receptor for AGEs (RAGE) triggers oxidative stress and inflammation, which is the major deleterious effect of AGEs in host and intestinal microenvironment of diabetic and ageing conditions. The activation of AGEs-mediated RAGE could evoke nicotinamide adenine dinucleotide phosphate oxidase-induced reactive oxygen and nitrogen species production and subsequently give rise to oxidative stress in DKD and ageing kidney. Therefore, targeting RAGE with its ligands mediated oxidative stress and chronic inflammation is considered as an additional intervention strategy for DKD and ageing kidney. In this review, we summarize AGEs/RAGE-mediated oxidative stress and inflammation signaling pathways in DKD and ageing kidney, discussing opportunities and challenges of targeting at AGEs/RAGE-induced oxidative stress that could hold the promising potential approach for improving DKD and ageing kidney.

Reprogramming of microRNA expression via E2F1 downregulation promotes Salmonella infection both in infected and bystander cells

Cells infected with pathogens can contribute to clearing infections by releasing signals that instruct neighbouring cells to mount a pro-inflammatory cytokine response, or by other mechanisms that reduce bystander cells’ susceptibility to infection. Here, we show the opposite effect: epithelial cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells. We find that the endoplasmic reticulum stress response is activated in both infected and bystander cells, and this leads to activation of JNK pathway, downregulation of transcription factor E2F1, and consequent reprogramming of microRNA expression in a time-dependent manner. These changes are not elicited by infection with other bacterial pathogens, such as Shigella flexneri or Listeria monocytogenes. Remarkably, the protein HMGB1 present in the secretome of Salmonella-infected cells is responsible for the activation of the IRE1 branch of the endoplasmic reticulum stress response in non-infected, neighbouring cells. Furthermore, E2F1 downregulation and the associated microRNA alterations promote Salmonella replication within infected cells and prime bystander cells for more efficient infection.

Cells infected with pathogens can release signals that instruct neighbouring cells to mount an immune response or that reduce these cells’ susceptibility to infection. Here, Aguilar et al. show the opposite effect: cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells by activating their ER-stress response.

Congenital Unilateral Renal Aplasia in a Cynomolgus Monkey (Macaca fascicularis) With Investigation Into Potential Pathogenesis

We describe and characterize unilateral renal aplasia in a cynomolgus monkey (Macaca fascicularis) from a chronic toxicology study adding to the limited histopathology reports of congenital renal anomalies in macaques. In the current case, the affected kidney was macroscopically small and characterized microscopically by a thin cortex with an underdeveloped medulla and an absent papilla. The remnant medulla lacked a corticomedullary junction and contained only a few irregular collecting duct-like structures. The cortex had extensive interstitial mature collagen deposition with fibromuscular collar formation around Bowman's capsules. Due to parenchymal collapse, mature glomeruli were condensed together with occasional atrophic and sclerotic glomeruli. The majority of the cortical tubules were poorly differentiated with only small islands of fully developed cortical tubules present. Histochemical and immunohistochemical stains were utilized to demonstrate key diagnostic features of this congenital defect, to assist with differentiating it from renal dysplasia, and to provide potential mechanistic pathways. Immunostaining (S100, paired box gene 2 [PAX2], aquaporins) of the medulla was compatible with incomplete maturation associated with aplasia, while the immunostaining profile for the cortex (vimentin, calbindin, PAX2-positive cortical tubules, and smooth muscle actin-positive fibromuscular collars) was most compatible with dedifferentiation secondary to degenerative changes.

Pyruvate-Enriched Oral Rehydration Solution Improves Glucometabolic Disorders in the Kidneys of Diabetic db/db Mice

Diabetes is prevalent worldwide, but ideally intensive therapeutic strategy in clinical diabetes and diabetic nephropathy (DN) is still lack. Pyruvate is protective from glucometabolic disturbances and kidney dysfunction in various pathogenic insults. Present studies focused on oral pyruvate effects on diabetes status and DN with 0.35% pyruvate in pyruvate-enriched oral rehydration solution (Pyr-ORS) and 1% pyruvate as drinking water for 8 weeks, using the model of diabetic db/db mice. Both Pyr-ORS and 1% pyruvate showed comparable therapeutic effectiveness with controls of body weight and blood sugar, increases of blood insulin levels, and improvement of renal function and pathological changes. Aberrant key enzyme activities in glucometabolic pathways, AR, PK, and PDK/PDH, were also restored; indexes of oxidative stress and inflammation, NAD⁺/NADH ratio, and AGEs in the kidneys were mostly significantly preserved after pyruvate treatments. We concluded that oral pyruvate delayed DN progression in db/db mice and the modified Pyr-ORS formula might be an ideal novel therapeutic drink in clinical prevention and treatment of type 2 diabetes and DN.