Acute Kidney Injury Is Aggravated By Excessive Epithelial Stress Response Induced By Glucocorticoids

acute kidney injury (AKI) is a challenging clinical problem associated with high morbidity and mortality, and is a common complication in critically ill patients with COVID-19. In acute kidney injury, tubular epithelial cells (TEC) are the main part of injury, and the recovery of acute kidney injury depends on the plasticity of TEC [1]. In the kidney with acute injury, the appropriate stress response promotes the proper activation of the repair mechanism, so that the kidney can be completely repaired after injury [1]. However, if the kidney stress response is excessive, the damage caused by AKI cannot be completely repaired and progresses to chronic kidney injury (CKD), and even leads to chronic kidney disease and kidney failure [2]. Since the stress response caused by AKI predicts the progression of CKD, preventing or stopping adverse stress reactions is of core clinical importance not only in the acute injury stage, but also in the post-injury repair stage [3]. However, the cellular mechanism by which renal tubular epithelial cells respond to stress is not fully understood, and there is still no consensus on whether glucocorticoids should be used during acute renal injury.

Click to Cistanche for kidney disease

Recently, The article Glucocorticoids induce a maladaptive, led by Postdoctoral Zhou Luping, member of Xu Yong's research team, Department of Endocrinology, Affiliated Hospital of Southwest Medical University, as the first author and Professor Thomas Worzfeld, Institute of Pharmacology, University of Marburg, Germany, as the corresponding author epithelial stress response to aggravate acute kidney injury is published online in the journal Science Translational Medicine. Through RNA seq, ATAC seq, renal TEC glucocorticoid receptor (GR) specific knockout, DNA damage and metabolic analysis, this study revealed the molecular mechanism and pharmacological targets of TEC adverse stress response in acute injury and repair. It provides a new perspective for further understanding of acute renal injury exacerbated by synthetic glucocorticoids (such as dexamethasone).

In this study, we first conducted a cohort study of COVID-19 patients, and found that 64% of severe COVID-19 patients with AKI had myoglobin deposition in TEC, indicating that myoglobin damage to TEC is the main pathophysiological mechanism of severe COVID-19 AKI.

Therefore, the authors used myoglobin to build AKI mouse models and observed the effects of dexamethasone with or without the synthetic glucocorticoid on the kidney of mice with acute injury. The results showed that dexamethasone increased kidney damage! What is the molecular mechanism? In order to answer this question, the author established for the first time an in vitro model of acute kidney injury - in vitro 3D model of renal tubuloids, referred to as "tubuloids" [4]. It was found that stimulation of myoglobin up-regulated the expression of tubuloids oxidative stress-related genes and Ngal, a marker of renal tubuloids damage. Na-seq analysis of tubuloids treated with myoglobin for 12 h showed that myoglobin activated the inflammatory response and apoptosis of tubuloids, and the activation of these inflammatory signals is at least partially regulated by NF-κB. Subsequently, myoglobin treated tubuloids were treated as ATAC-seq, and the results again confirmed the regulatory role of NF-κB in myoglobin induced TEC injury. In addition, both transcription factor binding motif enrichment analysis and ATACseq analysis showed that myoglobin treated tubuloids increased binding of transcription factors that control cell differentiation and proliferation, including Klf4, Klf9, and Egr1.

Transcription analysis of tubuloids treated with myoglobin showed that Hsd11b2, the gene for editing the 11β-HSD2 enzyme, was significantly down-regulated (z-score:−0.9). 11β-HSD2 enzyme is a catalytic bioconversion enzyme that deactivates active 11β-hydroxy-glucocorticoids (such as cortisol or corticosterone) to 11-keto-glucocorticoids (such as cortisone or 11-dehydrocorticosterone) [5]. The authors then detected the expression of 11β-HSD2 enzyme in human and AKI animal models, and the results showed that 11β-HSD2 enzyme was significantly down-regulated in human and AKI animal models, while the phosphorylation (activation state of GR) was significantly up-regulated. Does acute kidney injury lead to the activation of glucocorticoid receptors by inhibiting the inactivation of endogenous active glucocorticoids? To answer this question, the authors conducted two independent experiments: 1. AKI mice were treated with the steroid 11β-hydroxylase inhibitor metyrapone to observe the effect of blocking endogenous glucocorticoid formation on AKI; 2. 2. A transgenic mouse was constructed, in which the gene Nr3c1 encoding GR was specifically inactivated in TEC (genotype Pax8-Cre), and the effect of specific knockout of GR in TEC on AKI was observed. The results showed that the application of metyrapone and the specific knockout of GR had obvious protective effect on the kidney. In summary, endogenous glucocorticoid receptor activation induced by AKI aggravates TEC injury.

In order to analyze the mechanism by which GR activation aggravates TEC injury, the authors treated tubuloids with myoglobin and observed the effect of dexamethasone with or without dexamethasone on TEC injury by RNAseq. The results showed that dexamethasone up-regulated the expression of TEC injury index Krt20. Interestingly, dexamethasone did not show the expected anti-inflammatory effect in the data in this paper, but increased the DNA damage of TEC and inhibited the expression of genes related to DNA double strand repair. These include Bard1, Blm, Brca1, Brca2, Brip1, Dna2, Exo1, Fancd2, Mre11, Rad51, Rad51ap1, Rad54l, Rpa2, Xrcc2, and Xrcc3.

DNA damage and repair are closely related to cell metabolism [6]. GR signal plays an important role in regulating energy metabolism of skeletal muscle, liver and adipose tissue cells [7]. Therefore, the authors continued to explore the role of dexamethasone on cell metabolism. Both human kidney tissue staining and in vitro culture showed that dexamethasone up-regulated the expression of stress response gene Fkbp51, inhibited the expression of mTORC1, a major complex of cell metabolism, and the activation of S6, a downstream signal of mTOR. mTORC1 is known to promote protein translation [8], so we injected puromycin into AKI mouse models to assess the effect of GR knockout on protein synthesis after kidney injury in mice. The results showed that GR knockout significantly increased protein synthesis after injury. However, pharmacological blocking of the mTOR signaling pathway - the application of rapamycin - blocked the protective effect of GR knockout on the kidney. Taken together, these data confirm the regulatory role of mTOR signaling pathway in GR-mediated TEC adverse stress response.

mTOR signal is closely related to mitochondrial function [9]. Therefore, the authors concluded that GR signal activation and inhibition of mTOR may impair mitochondrial respiration in TEC, whereas GR knockout may stimulate mitochondrial respiration in TEC. The results showed that TEC specific GR knockout induced the enrichment of mitochondrial respiration related genes and up-regulated the expression of mitochondrial respiration related genes. This up-regulation of gene expression was not observed in healthy mice without AKI, underscoring the correlation between GR signaling and mitochondrial respiration under stress conditions. In addition, mitochondrial size in GR-specifically knocked out TEC was larger in myoglobin induced AKI mouse models compared to controls, and the use of dexamethasone inhibited mitochondrial respiratory function.

In summary, through the analysis of myoglobinuri-induced AKI mouse models and in vitro 3D models of human and mouse renal tubules, this paper reveals that endogenous glucocorticoids aggravate the injury of TEC by activating GR signals, while the use of synthetic glucocorticoids aggravates the adverse stress response caused by glucocorticoid receptor signaling in damaged TEC. This adverse stress response obstructs transcriptional programs required for DNA repair, amplifies damage-induced DNA double-strand breaks, and inhibits mTOR activity and mitochondrial bioenergy. The authors specifically knocked out TEC GR, which effectively reversed the damage to TEC caused by acute kidney injury, and this protective effect depended on the protection of transcriptional programs required for DNA repair and the maintenance of mTOR activity and the bioenergetic normal function of mitochondria.

How Does Cistanche Treat Kidney Disease?

Cistanche is a traditional Chinese herbal medicine used for centuries to treat various health conditions, including kidney disease. It is derived from the dried stems of Cistanche deserticola, a plant native to the deserts of China and Mongolia. The main active components of cistanche are phenylethanoid glycosides, echinacoside, and acteoside, which have been found to benefit kidney health.

Kidney disease, also known as renal disease, refers to a condition in which the kidneys are not functioning properly. This can result in a buildup of waste products and toxins in the body, leading to various symptoms and complications. Cistanche may help treat kidney disease ase through several mechanisms.

Firstly, cistanche has been found to have diuretic properties, meaning it can increase urine production and help eliminate waste products from the body. This can help relieve the burden on the kidneys and prevent the buildup of toxins. By promoting diuresis, cistanche may also help Reduce high blood pressure, a common complication of kidney disease.

Moreover, cistanche has been shown to have antioxidant effects. Oxidative stress, caused by an imbalance between the production of free radicals and the body's antioxidant defenses, plays a key role in the progression of kidney disease. ies help neutralize free radicals and reduce Oxidative stress, thereby protecting the kidneys from damage. The phenylethanoid glycosides found in cistanche have been particularly effective in scavenging free radicals and inhibiting lipid peroxidation.

Additionally, cistanche has been found to have anti-inflammatory effects. Inflammation is another key factor in the development and progression of kidney disease. Cistanche's anti-inflammatory properties help reduce the production of pro-inflammatory cytokines and inhibit the activation of inflammation mandatory pathways, thus alleviating inflammation in the kidneys.

Furthermore, cistanche has been shown to have immunomodulatory effects. In kidney disease, the immune system can be dysregulated, leading to excessive inflammation and tissue damage. Cistanche helps regulate the immune response by modulating the production and activity of immune cells, such as T cells and macrophages. This immune regulation helps reduce inflammation and prevent further damage to the kidneys.

Moreover, cistanche has been found to improve renal function by promoting the regeneration of renal tubes with cells. Renal tubular epithelial cells play a crucial role in the filtration and reabsorption of waste products and electrolytes. In kidney disease, these cells can be damaged, leading to damaged renal function. Cistanche's ability to promote the regeneration of these cells helps restore proper renal function and improve overall kidney health.

In addition to these direct effects on the kidneys, cistanche has been found to have beneficial effects on other organs and systems in the body. This holistic approach to health is particularly important in kidney disease, as the condition often affects multiple organs and systems. che has been shown to have protective effects on the liver, heart, and blood vessels, which are commonly affected by kidney disease. By promoting the health of these organs, cistanche helps improve overall kidney function and prevent further complications.

In conclusion, cistanche is a traditional Chinese herbal medicine used for centuries to treat kidney disease. Its active components have diuretic, antioxidant, anti-inflammatory, immunomodulatory, and regenerative effects, which help improve renal function and protect the kidneys from further damage. , cistanche has beneficial effects on other organs and systems, making it a holistic approach to treating kidney disease.