Krisztian Stadler

Atrial Natriuretic Peptide (ANP) plays an important role in blood pressure regulation. Low levels of ANP correlate with the development of salt‐sensitive hypertension (SS‐HTN). Our previous studies indicated that ANP deficiency exacerbated renal function decline in SS‐HTN. In the heart and fat tissue, ANP was reported to affect lipid peroxidation and mitochondrial bioenergetics but the effects of ANP on mitochondrial function in the kidney are unexplored. We hypothesized that ANP deficiency in SS‐HTN causes renal bioenergetic shift, leading to disruption of mitochondrial network and oxidative stress. To address the hypothesis, we placed Dahl SS wild‐type (SS ^WT ) and ANP knockout (SS ^NPPA−/− ) rats on 4% NaCl high salt (HS) diet to induce HTN or maintained them on 0.4% NaCl normal salt (NS) diet and assessed mitochondrial bioenergetics and dynamics using spectrofluorimetry, Seahorse assay, electron paramagnetic resonance (EPR) spectroscopy, Western blotting, electron microscopy, PCR and cytokine assays. We report that under high salt conditions, associated with hypertension and renal damage, the SS ^NPPA−/− rats exhibit a decrease in mitochondrial membrane potential and elevation in mitochondrial ROS levels compared to SS ^WT . The redox shift is also evident by the presence of more pronounced medullar lipid peroxidation in the SS ^NPPA−/− strain. We also revealed fragmented, more damaged mitochondria in the SS ^NPPA−/− rats, accompanied by increased turnover and biogenesis. Overall, our data indicate that ANP deficiency causes disruptions in mitochondrial bioenergetics and dynamics which likely contributes to aggravation of the renal damage and hypertension in the Dahl SS rat; the major pathological effects are evident in the groups subjected to a combined salt and ANP deficiency‐induced mitochondrial stress.

Our study demonstrated novel pathways affecting glomeruli under stress induced by dietary salt. Predictive gene correlation networks and bioinformatic semi-automatic analysis revealed changes in the pathways relevant to mitochondrial function, inflammatory, apoptotic/fibrotic processes, and cell calcium transport.

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as “oxidative stress” or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or “redox signaling.” The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

The importance of healthy mitochondrial function is implicated in the prevention of chronic kidney disease (CKD) and diabetic kidney disease (DKD). Sex differences also play important roles in DKD. Our previous studies revealed that mitochondrial substrate overload (modeled by homozygous deletion of carnitine acetyl-transferase [CrAT]) in proximal tubules causes renal injury. Here, we demonstrate the importance of intact mitochondrial substrate efflux by titrating the amount of overload through the generation of a heterozygous CrAT-KO model (PT-CrAT ^HET mouse). Intriguingly, these animals developed renal injury similarly to their homozygous counterparts. Mitochondria were structurally and functionally impaired in both sexes. Transcriptomic analyses, however, revealed striking sex differences. Male mice shut down fatty acid oxidation and several other metabolism-related pathways. Female mice had a significantly weaker transcriptional response in metabolism, but activation of inflammatory pathways was prominent. Proximal tubular cells from PT-CrAT ^HET mice of both sexes exhibited a shift toward a more glycolytic phenotype, but female mice were still able to oxidize fatty acid–based substrates. Our results demonstrate that maintaining mitochondrial substrate metabolism balance is crucial to satisfying proximal tubular energy demand. Our findings have potentially broad implications, as both the glycolytic shift and the sexual dimorphisms discovered herein offer potentially new modalities for future interventions for treating kidney disease.

Post-traumatic stress disorder (PTSD) is associated with cognitive deficits, oxidative stress, and inflammation. Animal models have recapitulated features of PTSD, but no comparative RNA sequencing analysis of differentially expressed genes (DEGs) in the brain between PTSD and animal models of traumatic stress has been carried out. We compared DEGs from the prefrontal cortex (PFC) of an established stress model to DEGs from the dorsolateral PFC (dlPFC) of humans. We observed a significant enrichment of rat DEGs in human PTSD and identified 20 overlapping DEGs, of which 17 (85%) are directionally concordant. N,N-dimethyltryptamine (DMT) is a known indirect antioxidant, anti-inflammatory, and neuroprotective compound with antidepressant and plasticity-facilitating effects. We tested the capacity of DMT, the monoamine oxidase inhibitor (MAOI) harmaline, and “pharmahuasca” (DMT + harmaline) to reduce reactive oxygen species (ROS) production and inflammatory gene expression and to modulate neuroplasticity-related gene expression in the model. We administered DMT (2 mg/kg IP), harmaline (1.5 mg/kg IP), pharmahuasca, or vehicle every other day for 5 days, following a 30 day stress regiment. We measured ROS production in the PFC and hippocampus (HC) by electron paramagnetic resonance spectroscopy and sequenced total mRNA in the PFC. We also performed in vitro assays to measure the affinity and efficacy of DMT and harmaline at 5HT_2AR compared to 5-HT. DMT and pharmahuasca reduced ROS production in the PFC and HC, while harmaline had mixed effects. Treatments normalized 9, 12, and 14 overlapping DEGs, and pathway analysis implicated that genes were involved in ROS production, inflammation, growth factor signaling, neurotransmission, and neuroplasticity.

Long-term protein restriction is not advantageous for an otherwise healthy, aging kidney, as it facilitates the development of renal tubular injury and inflammatory cell infiltration. We provide evidence using FGF21 knockout animals that FGF21 is essential to counteract the renal injury and inflammation during aging on a low-protein diet.

Introduction: Sex differences are implicated in many cardiovascular and renal pathologies; for instance, premenopausal females are typically less prone to renovascular damage than males. However, although mitochondrial bioenergetics per se is a well‐known factor that can mediate the progression of the renal diseases, it is not known if there are sex‐related dissimilarities in the performance of renal mitochondria prior to the development of any disease. The goal of this study was to test the differences in renal cortical and medullary mitochondrial function in healthy male versus female rats. Methods: . Mitochondria were isolated from the kidneys collected from male and female Sprague Dawley (SD) rats procured from Charles River labs at 11 weeks of age. Mitochondrial membrane potential, superoxide and H ₂ O ₂ levels were measured with luminescent or fluorescent dyes (TMRM, MCLA and Amplex Red) in mitochondria isolated from renal cortex and medulla. To measure the oxygen consumption rate (OCR) and mitochondrial calcium uptake, seahorse assay and spectrofluorimetry with CaGreen dye, respectively, were performed on isolated mitochondria. Lipid peroxide radical formation was detected using electron spin resonance spectroscopy (ESR) with in vivo spin trapping. The SOD activity and total antioxidant capacity were measured using commercially available kits. In order to analyze the expression levels of various mitochondria‐related proteins, Western blot analysis was performed on snap‐frozen isolated renal mitochondria. Results: . Kidneys from SD male (SD ^M ) and female rats (SD ^F ) were divided into cortex (SD ^{MC, FC} ) and medulla (SD ^{MM, FM} ). We report higher membrane potential in SD ^FM compared to SD ^MM (p2 O ₂ levels were elevated in both the SD ^FC and SD ^FM mitochondria compared to SD ^M (pFM samples. Interestingly, superoxide production was increased in the medulla compared to the cortex for both SD ^M and SD ^F , while SOD2 expression was similar. Total SOD activity was increased in SD ^FC compared to all other groups (pFM tissues compared to other groups (p<0.05). Female mitochondria exhibited decreased OCR compared to males, and all OCR parameters were lower in medullary vs cortical mitochondria, independent of sex. Interestingly, calcium uptake was more active in the medulla vs cortex for both males and females, whereas the mitochondrial permeability transition pore (mPTP) opening was recorded earlier in females than males. Conclusions: . We report differences in mitochondrial function in the cortex and medulla of young healthy male and female rats, primarily, in their ability to handle reactive oxygen species. The observed sex‐related dissimilarities open new avenues of research aimed at establishing the mechanisms that may affect the predisposition of males and females to kidney disease development later in life.