Activation of hypoxia-sensing pathways promotes renal ischemic preconditioning following myocardial infarction

Potential of 68Ga-FAPI-04 PET/MR to predict worsening renal function after acute ST-elevation myocardial infarction

PURPOSE

The fibroblast activation protein inhibitor-04 (FAPI-04) specifically binds to the FAP of activated myocardial fibroblasts, which makes 68Ga-labelled FAPI-04 (68Ga-FAPI-04) positron emission tomography (PET)/magnetic resonance (MR) a new potential imaging technique for the evaluation of myocardial fibrosis. This study aimed to evaluate the potential value of 68Ga-FAPI-04 PET/MR in assessing and predicting changes in renal function in patients with acute ST-elevation myocardial infarction (STEMI).

METHODS

Thirty-three patients with STEMI were included in this study. 68Ga-FAPI-04 PET/MR and cardiac magnetic resonance were performed before discharge in all patients. Worsening renal function(WRF) was defined as ≥20% decrease in estimated glomerular filtration rate(eGFR) from baseline to 12 months.

RESULTS

The WRF group demonstrated higher 68Ga-FAPI-04 uptake volume (UV) at baseline than the non-WRF group(P = 0.009). 68Ga-FAPI-04 UV at baseline was correlated with follow-up eGFR (r = -0.493, P = 0.004). 68Ga-FAPI-04 UV at baseline was a significant predictor of WRF (OR = 1.014, P = 0.029) at 12 months after STEMI.

CONCLUSIONS

As an effective tool to non-invasively quantify myocardial fibroblast activation, 68Ga-FAPI-04 PET/MR has potential value for assessing and predicting worsening renal function in patients with STEMI.

Low potassium activation of proximal mTOR/AKT signaling is mediated by Kir4.2

The renal epithelium is sensitive to changes in blood potassium (K+). We identify the basolateral K+ channel, Kir4.2, as a mediator of the proximal tubule response to K+ deficiency. Mice lacking Kir4.2 have a compensated baseline phenotype whereby they increase their distal transport burden to maintain homeostasis. Upon dietary K+ depletion, knockout animals decompensate as evidenced by increased urinary K+ excretion and development of a proximal renal tubular acidosis. Potassium wasting is not proximal in origin but is caused by higher ENaC activity and depends upon increased distal sodium delivery. Three-dimensional imaging reveals Kir4.2 knockouts fail to undergo proximal tubule expansion, while the distal convoluted tubule response is exaggerated. AKT signaling mediates the dietary K+ response, which is blunted in Kir4.2 knockouts. Lastly, we demonstrate in isolated tubules that AKT phosphorylation in response to low K+ depends upon mTORC2 activation by secondary changes in Cl- transport. Data support a proximal role for cell Cl- which, as it does along the distal nephron, responds to K+ changes to activate kinase signaling.

The versatile role of Serpina3c in physiological and pathological processes: a review of recent studies

Murine Serpina3c belongs to the family of serine protease inhibitors (Serpins), clade "A" and its human homologue is SerpinA3. Serpina3c is involved in some physiological processes, including insulin secretion and adipogenesis. In the pathophysiological process, the deletion of Serpina3c leads to more severe metabolic disorders, such as aggravated non-alcoholic fatty liver disease (NAFLD), insulin resistance and obesity. In addition, Serpina3c can improve atherosclerosis and regulate cardiac remodeling after myocardial infarction. Many of these processes are directly or indirectly mediated by its inhibition of serine protease activity. Although its function has not been fully revealed, recent studies have shown its potential research value. Here, we aimed to summarize recent studies to provide a clearer view of the biological roles and the underlying mechanisms of Serpina3c.

Renal fibrosis in type 2 cardiorenal syndrome: An update on mechanisms and therapeutic opportunities

Cardiorenal syndrome (CRS) is a state of coexisting heart failure and renal insufficiency in which acute or chronic dysfunction of the heart or kidney lead to acute or chronic dysfunction of the other organ.It was found that renal fibrosis is an important pathological process in the progression of type 2 CRS to end-stage renal disease, and progressive renal impairment accelerates the deterioration of cardiac function and significantly increases the hospitalization and mortality rates of patients. Previous studies have found that Hemodynamic Aiteration, RAAS Overactivation, SNS Dysfunction, Endothelial Dysfunction and Imbalance of natriuretic peptide system contribute to the development of renal disease in the decompensated phase of heart failure, but the exact mechanisms is not clear. Therefore, in this review, we focus on the molecular pathways involved in the development of renal fibrosis due to heart failure and identify the canonical and non-canonical TGF-β signaling pathways and hypoxia-sensing pathways, oxidative stress, endoplasmic reticulum stress, pro-inflammatory cytokines and chemokines as important triggers and regulators of fibrosis development, and summarize the therapeutic approaches for the above signaling pathways, including SB-525334 Sfrp1, DKK1, IMC, rosarostat, 4-PBA, etc. In addition, some potential natural drugs for this disease are also summarized, including SQD4S2, Wogonin, Astragaloside, etc.

Is Renal Ischemic Preconditioning an Alternative to Ameliorate the Short- and Long-Term Consequences of Acute Kidney Injury?

Acute kidney injury (AKI) is a global health problem and has recently been recognized as a risk factor for developing chronic kidney disease (CKD). Unfortunately, there are no effective treatments to reduce or prevent AKI, which results in high morbidity and mortality rates. Ischemic preconditioning (IPC) has emerged as a promising strategy to prevent, to the extent possible, renal tissue from AKI. Several studies have used this strategy, which involves short or long cycles of ischemia/reperfusion (IR) prior to a potential fatal ischemic injury. In most of these studies, IPC was effective at reducing renal damage. Since the first study that showed renoprotection due to IPC, several studies have focused on finding the best strategy to activate correctly and efficiently reparative mechanisms, generating different modalities with promising results. In addition, the studies performing remote IPC, by inducing an ischemic process in distant tissues before a renal IR, are also addressed. Here, we review in detail existing studies on IPC strategies for AKI pathophysiology and the proposed triggering mechanisms that have a positive impact on renal function and structure in animal models of AKI and in humans, as well as the prospects and challenges for its clinical application.

Kidney collecting duct cells make vasopressin in response to NaCl-induced hypertonicity

Vasopressin has traditionally been thought to be produced by the neurohypophyseal system and then released into the circulation where it regulates water homeostasis. The questions of whether vasopressin could be produced outside of the brain and if the kidney could be a source of vasopressin are raised by the syndrome of inappropriate antidiuretic hormone secretion (vasopressin). We found that mouse and human kidneys expressed vasopressin mRNA. Using an antibody that detects preprovasopressin, we found that immunoreactive preprovasopressin protein was found in mouse and human kidneys. Moreover, we found that murine collecting duct cells made biologically active vasopressin, which increased in response to NaCl-mediated hypertonicity, and that water restriction increased the abundance of kidney-derived vasopressin mRNA and protein expression in mouse kidneys. Thus, we provide evidence of biologically active production of kidney-derived vasopressin in kidney tubular epithelial cells.

Kir4.2 mediates proximal potassium effects on glutaminase activity and kidney injury

Inadequate potassium (K+) consumption correlates with increased mortality and poor cardiovascular outcomes. Potassium effects on blood pressure have been described previously; however, whether or not low K+ independently affects kidney disease progression remains unclear. Here, we demonstrate that dietary K+ deficiency causes direct kidney injury. Effects depend on reduced blood K+ and are kidney specific. In response to reduced K+, the channel Kir4.2 mediates altered proximal tubule (PT) basolateral K+ flux, causing intracellular acidosis and activation of the enzyme glutaminase and the ammoniagenesis pathway. Deletion of either Kir4.2 or glutaminase protects from low-K+ injury. Reduced K+ also mediates injury and fibrosis in a model of aldosteronism. These results demonstrate that the PT epithelium, like the distal nephron, is K+ sensitive, with reduced blood K+ causing direct PT injury. Kir4.2 and glutaminase are essential mediators of this injury process, and we identify their potential for future targeting in the treatment of chronic kidney disease.

Kallistatin/Serpina3c inhibits cardiac fibrosis after myocardial infarction by regulating glycolysis via Nr4a1 activation

BACKGROUND

Fibrotic remodeling is an essential aspect of heart failure. Human kallistatin (KS, mouse Serpina3c homologs) inhibits fibrosis after myocardial infarction (MI) but the specific underlying mechanism is unknown.

METHODS

A total of 40 heart failure patients (HFPs) were enrolled and their plasma KS was measured using ELISA. Serpina3c^-/- and C57BL/6 mice were used to construct the MI model. TGF-β1 or a hypoxic condition was established to interfere with the functioning of cardiac fibroblasts (CFs). RNA-seq was performed to assess the effect of Serpina3c on the transcriptome.

FINDINGS

The levels of KS were used as a predictor of readmission among the HFPs. Serpina3c expression decreased in MI hearts and CFs. Serpina3c^-/- led to the aggravation of MI fibrosis, and increased the proliferation of CFs. The overexpression of Serpina3c in CFs had the opposite effect. Glycolysis-related genes were significantly increased in Serpina3c^-/- group by RNA-seq. Enolase (ENO1), which is a key enzyme in glycolysis, increased most significantly. Inhibition of ENO1 could antagonize the promotion of Serpina3c^-/- on the proliferation of CFs. Co-IP was performed to verify the interaction between Serpina3c and Nr4a1. Serpina3c^-/- inhibited the acetylation of Nr4a1 and increased the degradation of Nr4a1. Activation of Nr4a1 could negatively regulate the expression of ENO1 and inhibited the proliferation of Serpina3c^-/- CFs in Serpina3c^-/- MI mice.

INTERPRETATION

Serpina3c inhibits the transcriptional activation of ENO1 by regulating the acetylation of Nr4a1, thereby reducing the fibrosis after MI by inhibiting glycolysis. Serpina3c is a potential target for prevention and treatment of heart failure after MI.

Macrophage interferon regulatory factor 4 deletion ameliorates aristolochic acid nephropathy via reduced migration and increased apoptosis

Aristolochic acid (AA) is the causative nephrotoxic alkaloid in aristolochic acid nephropathy, which results in a tubulointerstitial fibrosis. AA causes direct proximal tubule damage. There is also an influx of macrophages, although their role in the pathogenesis is poorly understood. Here we demonstrate that AA directly stimulates migration, inflammation, and reactive oxygen species (ROS) production in macrophages ex vivo. Cells lacking interferon regulatory factor 4 (IRF4), a known regulator of macrophage migration and phenotype, had a reduced migratory response, though effects on ROS production and inflammation were preserved or increased relative to wild-type cells. Macrophage-specific IRF4 knockout mice were protected from both acute and chronic kidney effects of AA administration based on functional and histological analysis. Renal macrophages from kidneys of AA-treated macrophage-specific IRF4 knockout mice demonstrated increased apoptosis and ROS production compared with wildtype controls, indicating that AA directly polarizes macrophages to a promigratory and proinflammatory phenotype. However, knockout mice had reduced renal macrophage abundance following AA administration. While macrophages lacking IRF4 can adopt a proinflammatory phenotype upon AA exposure, their inability to migrate to the kidney and increased rates of apoptosis upon infiltration provide protection from AA in vivo. These results provide evidence of direct AA effects on macrophages in AAN and add to the growing body of evidence that supports a key role of IRF4 in modulating macrophage function in kidney injury.

Clinical Pharmacokinetics and Pharmacodynamics of Roxadustat

The pharmacokinetics of roxadustat are well characterized, with an apparent volume of distribution after oral administration of 22–57 L, apparent clearance of 1.2–2.65 L/h, and renal clearance of 0.030–0.026 L/h in healthy volunteers; the elimination half-life is 9.6–16 h. Plasma binding is 99% and the fraction eliminated by hemodialysis is 2.34%. As an interpretation of the pharmacodynamics of roxadustat, we proposed a concept with a hypothetical cascade of two subsequent effects, first on erythropoetin (EPO) and second on hemoglobin (delta Hb). The primary effect on EPO is observed within a few hours after roxadustat administration and can be modeled using the sigmoidal Hill equation. The concentration at half-maximum effect can be inferred at 10–36 µg/mL, the Hill coefficient at 3.3, and the effect bisection time at 10–17 h, corresponding to EPO half-life. The subsequent effect on hemoglobin (delta Hb) is observed after several weeks and can be interpreted as an irreversible, dose proportional, unsaturable effect, continuing in agreement with the lifespan of red blood cells of 63–112 days.