Therapeutic targeting of the mitochondrial dysfunction in septic acute kidney injury

Understanding Post-Sepsis Syndrome: How Can Clinicians Help?

Sepsis is a global health challenge, with over 49 million cases annually. Recent medical advancements have increased in-hospital survival rates to approximately 80%, but the escalating incidence of sepsis, owing to an ageing population, rise in chronic diseases, and antibiotic resistance, have also increased the number of sepsis survivors. Subsequently, there is a growing prevalence of "post-sepsis syndrome" (PSS). This syndrome includes long-term physical, medical, cognitive, and psychological issues after recovering from sepsis. PSS puts survivors at risk for hospital readmission and is associated with a reduction in health- and life span, both at short and long term, after hospital discharge. Comprehensive understanding of PSS symptoms and causative factors is vital for developing optimal care for sepsis survivors, a task of prime importance for clinicians. This review aims to elucidate our current knowledge of PSS and its relevance in enhancing post-sepsis care provided by clinicians.

PICK1 Deficiency Exacerbates Sepsis-Associated Acute Kidney Injury

We performed in vitro and in vivo experiments to explore the role of protein kinase C-binding protein 1 (PICK1), an intracellular transporter involved in oxidative stress-related neuronal diseases, in sepsis-related acute kidney injury (AKI). Firstly, PCR, western blotting, and immunohistochemistry were used to observe the expression of PICK1 after lipopolysaccharide- (LPS-) induced AKI. Secondly, by inhibiting PICK1 in vivo and silencing PICK1 in vitro, we further explored the effect of PICK1 on AKI. Finally, the relationship between PICK1 and oxidative stress and the related mechanisms were explored. We found that the expression of PICK1 was increased in LPS-induced AKI models both in vitro and in vivo. PICK1 silencing significantly aggravated LPS-induced apoptosis, accompanied by ROS production in renal tubular epithelial cells. FSC231, a PICK1-specific inhibitor, aggravated LPS-induced kidney injury. Besides, NAC (N-acetylcysteine), a potent ROS scavenger, significantly inhibited the PICK1-silencing-induced apoptosis. In conclusion, PICK1 might protect renal tubular epithelial cells from LPS-induced apoptosis by reducing excessive ROS, making PICK1 a promising preventive target in LPS-induced AKI.

Development of a photoacoustic microscopy technique to assess peritubular capillary function and oxygen metabolism in the mouse kidney

Microcirculatory changes and oxidative stress have long been associated with acute kidney injury. Despite substantial progress made by two-photon microscopy of microvascular responses to acute kidney injury in rodent models, little is known about the underlying changes in blood oxygen delivery and tissue oxygen metabolism. To fill this gap, we developed a label-free kidney imaging technique based on photoacoustic microscopy, which enables simultaneous quantification of hemoglobin concentration, oxygen saturation of hemoglobin, and blood flow in peritubular capillaries in vivo. Based on these microvascular parameters, microregional oxygen metabolism was quantified. We demonstrated the utility of this technique by studying kidney hemodynamic and oxygen-metabolic responses to acute kidney injury in mice subject to lipopolysaccharide-induced sepsis. Dynamic photoacoustic microscopy of the peritubular capillary function and tissue oxygen metabolism revealed that sepsis induced an acute and significant reduction in peritubular capillary oxygen saturation of hemoglobin, concomitant with a marked reduction in kidney ATP levels and contrasted with nominal changes in peritubular capillary flow and plasma creatinine. Thus, our technique opens new opportunities to study microvascular and metabolic dysfunction in acute and chronic kidney diseases.

The application of omic technologies to research in sepsis-associated acute kidney injury

Acute kidney injury (AKI) is common in critically ill children and adults, and sepsis-associated AKI (SA-AKI) is the most frequent cause of AKI in the ICU. To date, no mechanistically targeted therapeutic interventions have been identified. High-throughput "omic" technologies (e.g., genomics, proteomics, metabolomics, etc.) offer a new angle of approach to achieve this end. In this review, we provide an update on the current understanding of SA-AKI pathophysiology. Omic technologies themselves are briefly discussed to facilitate interpretation of studies using them. We next summarize the body of SA-AKI research to date that has employed omic technologies. Importantly, omic studies are helping to elucidate a pathophysiology of SA-AKI centered around cellular stress responses, metabolic changes, and dysregulation of energy production that underlie its clinical features. Finally, we propose opportunities for future research using clinically relevant animal models, integrating multiple omic technologies and ultimately progressing to translational human studies focusing therapeutic strategies on targeted disease mechanisms.

NMR-based serum and urine metabolomic profile reveals suppression of mitochondrial pathways in experimental sepsis-associated acute kidney injury

Sepsis-associated acute kidney injury (SA-AKI) is a significant problem in the critically ill that causes increased death. Emerging understanding of this disease implicates metabolic dysfunction in its pathophysiology. This study sought to identify specific metabolic pathways amenable to potential therapeutic intervention. Using a murine model of sepsis, blood and tissue samples were collected for assessment of systemic inflammation, kidney function, and renal injury. Nuclear magnetic resonance (NMR)-based metabolomics quantified dozens of metabolites in serum and urine that were subsequently submitted to pathway analysis. Kidney tissue gene expression analysis confirmed the implicated pathways. Septic mice had elevated circulating levels of inflammatory cytokines and increased levels of blood urea nitrogen and creatinine, indicating both systemic inflammation and poor kidney function. Renal tissue showed only mild histological evidence of injury in sepsis. NMR metabolomic analysis identified the involvement of mitochondrial pathways associated with branched-chain amino acid metabolism, fatty acid oxidation, and de novo NAD⁺ biosynthesis in SA-AKI. Renal cortical gene expression of enzymes associated with those pathways was predominantly suppressed. Renal cortical fatty acid oxidation rates were lower in septic mice with high inflammation, and this correlated with higher serum creatinine levels. Similar to humans, septic mice demonstrated renal dysfunction without significant tissue disruption, pointing to metabolic derangement as an important contributor to SA-AKI pathophysiology. Metabolism of branched-chain amino acid and fatty acids and NAD⁺ synthesis, which all center on mitochondrial function, appeared to be suppressed. Developing interventions to activate these pathways may provide new therapeutic opportunities for SA-AKI.NEW & NOTEWORTHY NMR-based metabolomics revealed disruptions in branched-chain amino acid metabolism, fatty acid oxidation, and NAD⁺ synthesis in sepsis-associated acute kidney injury. These pathways represent essential processes for energy provision in renal tubular epithelial cells and may represent targetable mechanisms for therapeutic intervention.

Exploring the pathophysiology of post-sepsis syndrome to identify therapeutic opportunities

Sepsis is a major health problem worldwide. As the number of sepsis cases increases, so does the number of sepsis survivors who suffer from “post-sepsis syndrome” after hospital discharge. This syndrome involves deficits in multiple systems, including the immune, cognitive, psychiatric, cardiovascular, and renal systems. Combined, these detrimental consequences lead to rehospitalizations, poorer quality of life, and increased mortality. Understanding the pathophysiology of these issues is crucial to develop new therapeutic opportunities to improve survival rate and quality of life of sepsis survivors. Such novel strategies include modulating the immune system and addressing mitochondrial dysfunction. A sepsis follow-up clinic may be useful to identify long-term health issues associated with post-sepsis syndrome and evaluate existing and novel strategies to improve the lives of sepsis survivors.

Protection of procyanidin B2 on mitochondrial dynamics in sepsis associated acute kidney injury via promoting Nrf2 nuclear translocation

In septic acute kidney injury (SAKI), the positive feedback between damaged mitochondria and accumulation of reactive oxygen species results in cell and tissue damage through multiple mechanisms. Removing the damaged mitochondria or neutralizing the reactive oxygen species has been considered beneficial to alleviating cell damage. The antioxidant Procyanidin B2 has been reported to inhibits reactive oxygen species and thereby reduces cell injury. However, it is unclear whether this effect is associated with clearance of damaged mitochondria. Here, we evaluated the efficacy of procyanidin B2 on SAKI, and focused on its effects on mitochondrial dynamics and removing damaged mitochondria via mitophagy. The results showed that the renal function, renal tubular cell vacuolization and oxidative stress were decreased in SAKI mice treated with procyanidin B2, moreover, skewed mitochondrial fusion/fission, mitochondrial mediated apoptosis and impaired mitophagy were improved in SAKI mice treated with procyanidin B2. In mechanism, the improvement of procyanidin B2 on mitochondrial dynamics were associated with increased nuclear translocation of the transcription factor, Nrf2. In summary, our findings highlighted that the protective efficacy of procyanidin B2 in reducing cellular damage in SAKI, and mechanisms improving mitochondrial dynamics and quality control at least in part by promoting Nrf2 translocation into the nucleus.

Rheb1 protects against cisplatin-induced tubular cell death and acute kidney injury via maintaining mitochondrial homeostasis

Ras homolog enriched in brain (Rheb1), a small GTPase, plays a crucial role in regulating cell growth, differentiation, and survival. However, the role and mechanisms for Rheb1 in tubular cell survival and acute kidney injury (AKI) remain unexplored. Here we found that Rheb1 signaling was activated in kidney tubule of AKI patients and cisplatin-treated mice. A mouse model of tubule-specific deletion of Rheb1 (Tubule-Rheb1^−/−) was generated. Compared to control littermates, Tubule-Rheb1^−/− mice were phenotypically normal within 2 months after birth but developed more severe kidney dysfunction, tubular cell death including apoptosis, necroptosis and ferroptosis, mitochondrial defect and less PGC-1α expression after cisplatin injection. In primary cultured tubular cells, Rheb1 ablation exacerbated cisplatin-induced cell death and mitochondrial defect. Furthermore, haploinsufficiency for Tsc1 in tubular cells led to Rheb1 activation and mitigated cisplatin-induced cell death, mitochondrial defect and AKI. Together, this study uncovers that Rheb1 may protect against cisplatin-induced tubular cell death and AKI through maintaining mitochondrial homeostasis.

Honokiol Attenuates Sepsis-Associated Acute Kidney Injury via the Inhibition of Oxidative Stress and Inflammation

Acute kidney injury (AKI) is one of the most common complications of sepsis, which largely contributes to the high mortality rate of sepsis. Honokiol, a natural polyphenol from the traditional Chinese herb Magnolia officinalis, is known to possess anti-inflammatory and antioxidant activity. Here, the underlying mechanism of honokiol-induced amelioration of sepsis-associated AKI was analyzed. The expression patterns of oxidative stress moleculars and TLRs-mediated inflammation pathway were examined to identify the response of NRK-52E cells incubated with septic rats' serum to honokiol. The levels of iNOS, NO, and myeloperoxidase in NRK-52E cells were increased during sepsis, which could be reversed by honokiol. The production of GSH and SOD as in vivo antioxidant was increased after honokiol treatment. The administration of honokiol significantly inhibited TLR2/4/MyD88 signaling pathway in AKI-induced NRK-52E cells. Furthermore, ZnPPIX, the HO-1 inhibitor, weakened honokiol-mediated morphological amelioration, and the reduced level of TNF-α, IL-1β, and IL-6 in kidneys of rats subjected to CLP. Finally, Honokiol was shown to connect with the Nrf2-Keap1 dimensionally. These findings suggest that honokiol plays its protective role on sepsis-associated AKI against oxidative stress and inflammatory signals.

Disturbance of mitochondrial dynamics and mitophagy in sepsis-induced acute kidney injury

AIMS

The renal tubule cells require a large number of mitochondria to supply ATP due to their high-energy demand during reabsorption and secretion against chemical gradients and result in mitochondria susceptible to disorder and injury during stress conditions. Injured mitochondria are eventually degraded by mitophagy, and disturbances in mitophagy are associated with the pathogenesis of acute kidney injury (AKI) such as diabetic nephropathy and glomerulosclerosis. However, whether a disturbance in mitophagy has occurred and the role it plays in (SAKI) is still unclear. Therefore, the aim of this study was to investigate the key features of mitophagy and mitochondrial dynamics in sepsis-induced acute kidney injury (SAKI).

MAIN METHODS

In this study, a murine septic AKI model induced by cecal ligation and puncture (CLP) was built; mitophagy and mitochondrial dynamics were measured in mice kidney in different time point.

KEY FINDINGS

The results showed that mitochondrial dynamics were characterized by fission/fusion aberrant, however more inclined to fission, and mitochondrial associated apoptosis was elevated over-time during SAKI. Furthermore, mitophagy was impaired in the later phase of SAKI, although elevated in early stage of SAKI. The results indicate that the underlying mechanisms of impaired mitophagy may associate with the cleavage of Parkin via caspases activated by NLRP3, at least partly.

SIGNIFICANCE

It is conceivable that this selective autophagic process and quality control machinery was impaired, leading to the accumulation of damaged mitochondria, oxidative stress, and cell death. Therefore, a targeted approach, by enhancing mitophagy during SAKI, may be a promising therapeutic strategy.

Cleistanthus collinus poisoning affects mitochondrial respiration and induces oxidative stress in the rat kidney

Cleistanthus collinus is a poisonous shrub used for deliberate self-harm in rural areas of South India and intake of boiled decoction of leaves is a common method of self-harm. Distal renal tubular acidosis (dRTA) is an important clinical symptom observed in C. collinus poisoning, and renal V-ATPases may be potential targets of damage. However, a lack of understanding of molecular mediators involved hampers medical management, which is mainly supportive. We hypothesized that C. collinus poisoning induces renal oxidative stress; probably by inducing mitochondrial uncoupling, which compromises V-ATPase activity to ultimately produce dRTA. This was tested by exposing renal BBMV, kidney cells in culture, and Wistar rats to C. collinus poisoning. Exposure to C. collinus aqueous extract resulted in significant elevations in the lipid peroxidation marker, conjugated dienes, in cell culture and in vivo. A significant decrease in mitochondrial respiratory control ratio was observed in kidneys from C. collinus-treated animals suggesting that mitochondrial oxidative phosphorylation is uncoupled. This was accompanied by significant increase in ADP levels and a decrease in proton pump activity. Thus, these results demonstrate that C. collinus poisoning induces oxidative stress which influences proton pump activity, probably due to feedback inhibition by elevated ADP levels because of mitochondrial dysfunction in the rat kidney.

Nanoscale Imaging of Kidney Glomeruli Using Expansion Pathology

Kidney glomerular diseases, such as the minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS), and other nephrotic syndromes, are typically diagnosed or confirmed via electron microscopy. Although optical microscopy has been a vital tool to examine clinical specimens for diagnoses in pathology for decades, the optical resolution is constricted by the physical diffraction limit of the optical microscope, which prevents high-resolution investigation of subcellular anatomy, such as of the podocyte tertiary foot processes. Here, we describe a simple, fast, and inexpensive protocol for nanoscale optical imaging of kidney glomeruli. The protocol is based on Expansion Pathology (ExPath), a new principle of microscopy that overcomes optical diffraction limit by chemically embedding specimens into a swellable polymer and physically expanding it homogenously prior to imaging. Our method uses only commercially available reagents, a conventional fluorescence microscope and it can be applied to both fixed-frozen or formalin-fixed paraffin embedded (FFPE) tissue sections. It requires minimal operative experience in a wet lab, optical microscopy and imaging processing. Finally, we also discuss challenges, limitations and prospective applications for ExPath-based imaging of glomeruli.

Cystathionine-γ-lyase expression is associated with mitochondrial respiration during sepsis-induced acute kidney injury in swine with atherosclerosis

Background

Sepsis is associated with disturbed glucose metabolism and reduced mitochondrial activity and biogenesis, ultimately leading to multiple organ dysfunction, e.g., acute kidney injury (AKI). Cystathionine-γ-lyase (CSE), the major cardiovascular source of endogenous H₂S release, is implicated in the regulation of glucose metabolism and mitochondrial activity through a PGC1α-dependent mechanism, and critical for kidney function. Atherosclerosis is associated with mitochondrial dysfunction and reduced CSE expression. Thus, the aim of this post hoc study was to test the hypothesis whether there is an interplay between CSE expression and kidney dysfunction, mitochondrial activity, and oxidative/nitrosative stress in porcine septic AKI with underlying coronary artery disease.

Methods

This study is a post hoc analysis of material from anesthetized and instrumented swine with a high fat diet-induced hypercholesterolemia and atherosclerosis undergoing faecal peritonitis-induced septic shock or sham procedure and intensive care (comprising fluid resuscitation and continuous i.v. noradrenaline (NoA) infusion) for 24 h. Glucose metabolism was quantified from blood ¹³C₆-glucose and expiratory ¹³CO₂/¹²CO₂ isotope enrichment during ¹³C₆-glucose infusion. Mitochondrial activity was determined by high-resolution respirometry. CSE and PGC1α expression, as well as nitrotyrosine formation and albumin extravasation, were quantified by immunohistochemistry of formalin-fixed kidney paraffin sections.

Results

Sepsis was associated with lactic acidosis (p = 0.004) and AKI (50% fall of creatinine clearance (CrCl), p = 0.019). While both whole-body glucose production (p = 0.004) and oxidation (p = 0.006) were increased, kidney tissue mitochondrial respiration was reduced (p = 0.028), coinciding with decreased CSE (p = 0.003) and PGC1α (p = 0.003) expression. Albumin extravasation (p = 0.011) and nitrotyrosine formation (p = 0.008) were increased in septic kidneys.

Conclusions

Sepsis-induced AKI is associated with disturbed mitochondrial respiration and biogenesis, which may be aggravated by oxidative and nitrosative stress. Our results confirm previous data in murine septic shock and porcine hemorrhage and resuscitation on the crucial role of CSE for barrier integrity and kidney function.

Electronic supplementary material

The online version of this article (10.1186/s40635-018-0208-z) contains supplementary material, which is available to authorized users.

RIPK3 promotes sepsis-induced acute kidney injury via mitochondrial dysfunction

Sepsis causes acute kidney injury (AKI) in critically ill patients, although the pathophysiology remains unclear. The receptor-interacting protein kinase-3 (RIPK3), a cardinal regulator of necroptosis, has recently been implicated in the pathogenesis of human disease. In mice subjected to polymicrobial sepsis, we demonstrate that RIPK3 promotes sepsis-induced AKI. Utilizing genetic deletion and biochemical approaches in vitro and in vivo, we identify a potentially novel pathway by which RIPK3 aggravates kidney tubular injury independently of the classical mixed lineage kinase domain-like protein-dependent (MLKL-dependent) necroptosis pathway. In kidney tubular epithelial cells, we show that RIPK3 promotes oxidative stress and mitochondrial dysfunction involving upregulation of NADPH oxidase-4 (NOX4) and inhibition of mitochondrial complex I and -III, and that RIPK3 and NOX4 are critical for kidney tubular injury in vivo. Furthermore, we demonstrate that RIPK3 is required for increased mitochondrial translocation of NOX4 in response to proinflammatory stimuli, by a mechanism involving protein-protein interactions. Finally, we observed elevated urinary and plasma RIPK3 levels in human patients with sepsis-induced AKI, representing potential markers of this condition. In conclusion, we identify a pathway by which RIPK3 promotes kidney tubular injury via mitochondrial dysfunction, independently of MLKL, which may represent a promising therapeutic target in sepsis-induced AKI.

MicroRNA-709 Mediates Acute Tubular Injury through Effects on Mitochondrial Function

Mitochondrial dysfunction has important roles in the pathogenesis of AKI, yet therapeutic approaches to improve mitochondrial function remain limited. In this study, we investigated the pathogenic role of microRNA-709 (miR-709) in mediating mitochondrial impairment and tubular cell death in AKI. In a cisplatin-induced AKI mouse model and in biopsy samples of human AKI kidney tissue, miR-709 was significantly upregulated in the proximal tubular cells (PTCs). The expression of miR-709 in the renal PTCs of patients with AKI correlated with the severity of kidney injury. In cultured mouse PTCs, overexpression of miR-709 markedly induced mitochondrial dysfunction and cell apoptosis, and inhibition of miR-709 ameliorated cisplatin-induced mitochondrial dysfunction and cell injury. Further analyses showed that mitochondrial transcriptional factor A (TFAM) is a target gene of miR-709, and genetic restoration of TFAM attenuated mitochondrial dysfunction and cell injury induced by cisplatin or miR-709 overexpression in vitro Moreover, antagonizing miR-709 with an miR-709 antagomir dramatically attenuated cisplatin-induced kidney injury and mitochondrial dysfunction in mice. Collectively, our results suggest that miR-709 has an important role in mediating cisplatin-induced AKI via negative regulation of TFAM and subsequent mitochondrial dysfunction. These findings reveal a pathogenic role of miR-709 in acute tubular injury and suggest a novel target for the treatment of AKI.

Metabolic Inflammatory Complex in Sepsis: Septic Cachexia as a Novel Potential Therapeutic Target

Despite several decades of focused investigation, sepsis remains a major cause of mortality in critically ill patients. Advancements in intensive care have enabled more patients to survive the acute phase of sepsis than previously, but a growing number of them progress to chronic critical illness. The failure of previous randomized clinical trials of anti-inflammatory agents to show any pro-survival benefit in septic patients underscores current thought that simple anti-inflammatory strategies are ineffective because the inhibitory effect of anti-inflammatory agents undermines the immune response to pathogens. New strategies with the dual capability of ameliorating inflammation in organs while stimulating antimicrobial activity are eagerly awaited. On the other hand, the metabolic alterations associated with systemic inflammatory response, including mitochondrial dysfunction and metabolic shift, are closely linked through a nexus of signaling pathways and signaling molecules. Preventing these metabolic derangements may be an alternative way to control excessive inflammation, an intriguing possibility that has not been fully explored. New insight into the molecular pathogenesis of sepsis and sepsis-associated chronic critical illness has led to the recognition of septic cachexia, a life-threatening form of metabolic inflammatory complex associated with multiple organ dysfunction. The potential for septic cachexia to serve as a novel target disease state to improve the clinical outcome of septic patients is discussed in this review.

Acute toll-like receptor 4 activation impairs rat renal microvascular autoregulatory behaviour

AIM

Little is known about how toll-like receptor 4 (TLR4) influences the renal microvasculature. We hypothesized that acute TLR4 stimulation with lipopolysaccharide (LPS) impairs afferent arteriole autoregulatory behaviour, partially through reactive oxygen species (ROS).

METHODS

We assessed afferent arteriole autoregulatory behaviour after LPS treatment (1 mg kg^-1 ; i.p.) using the in vitro blood-perfused juxtamedullary nephron preparation. Autoregulatory behaviour was assessed by measuring diameter responses to stepwise changes in renal perfusion pressure. TLR4 expression was assessed by immunofluorescence, immunohistochemistry and Western blot analysis in the renal cortex and vasculature.

RESULTS

Baseline arteriole diameter at 100 mmHg averaged 15.2 ± 1.2 μm and 12.2 ± 1.0 μm for control and LPS groups (P < 0.05) respectively. When perfusion pressure was increased in 15 mmHg increments from 65 to 170 mmHg, arteriole diameter in control kidneys decreased significantly to 69 ± 6% of baseline diameter. In the LPS-treated group, arteriole diameter remained essentially unchanged (103 ± 9% of baseline), indicating impaired autoregulatory behaviour. Pre-treatment with anti-TLR4 antibody or the TLR4 antagonist, LPS-RS, preserved autoregulatory behaviour during LPS treatment. P2 receptor reactivity was normal in control and LPS-treated rats. Pre-treatment with Losartan (angiotensin type 1 receptor blocker; (AT₁ ) 2 mg kg^-1 ; i.p.) increased baseline afferent arteriole diameter but did not preserve autoregulatory behaviour in LPS-treated rats. Acute exposure to Tempol (10^-3 mol L^-1 ), a superoxide dismutase mimetic, restored pressure-mediated vasoconstriction in kidneys from LPS-treated rats.

CONCLUSION

These data demonstrate that TLR4 activation impairs afferent arteriole autoregulatory behaviour, partially through ROS, but independently of P2 and AT₁ receptor activation.

Drp1-dependent mitophagy protects against cisplatin-induced apoptosis of renal tubular epithelial cells by improving mitochondrial function

Cisplatin chemotherapy often causes acute kidney injury (AKI) in cancer patients. There is increasing evidence that mitochondrial dysfunction plays an important role in cisplatin-induced nephrotoxicity. Degradation of damaged mitochondria is carried out by mitophagy. Although mitophagy is considered of particular importance in protecting against AKI, little is known of the precise role of mitophagy and its molecular mechanisms during cisplatin-induced nephrotoxicity. Also, evidence that activation of mitophagy improved mitochondrial function is lacking. Furthermore, several evidences have shown that mitochondrial fission coordinates with mitophagy. The aim of this study was to investigate whether activation of mitophagy protects against mitochondrial dysfunction and renal proximal tubular cells injury during cisplatin treatment. The effect of mitochondrial fission on mitophagy was also investigated. In cultured human renal proximal tubular cells, we observed that 3-methyladenine, a pharmacological inhibitor of autophagy, blocked mitophagy and exacerbated cisplatin-induced mitochondrial dysfunction and cells injury. In contrast, autophagy activator rapamycin enhanced mitophagy and protected against the harmful effects of cisplatin on mitochondrial function and cells viability. Suppression of mitochondrial fission by knockdown of its main regulator dynamin-related protein-1 (Drp1) decreased cisplatin-induced mitophagy. Meanwhile, Drp1 suppression protected against cisplatin-induced cells injury by inhibiting mitochondrial dysfunction. Our results provide evidence that Drp1-depedent mitophagy has potential as renoprotective targets for the treatment of cisplatin-induced AKI.

Mitochondrial energetics in the kidney

The kidney requires a large number of mitochondria to remove waste from the blood and regulate fluid and electrolyte balance. Mitochondria provide the energy to drive these important functions and can adapt to different metabolic conditions through a number of signalling pathways (for example, mechanistic target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) pathways) that activate the transcriptional co-activator peroxisome proliferator-activated receptor-γ co-activator 1α (PGC1α), and by balancing mitochondrial dynamics and energetics to maintain mitochondrial homeostasis. Mitochondrial dysfunction leads to a decrease in ATP production, alterations in cellular functions and structure, and the loss of renal function. Persistent mitochondrial dysfunction has a role in the early stages and progression of renal diseases, such as acute kidney injury (AKI) and diabetic nephropathy, as it disrupts mitochondrial homeostasis and thus normal kidney function. Improving mitochondrial homeostasis and function has the potential to restore renal function, and administering compounds that stimulate mitochondrial biogenesis can restore mitochondrial and renal function in mouse models of AKI and diabetes mellitus. Furthermore, inhibiting the fission protein dynamin 1-like protein (DRP1) might ameliorate ischaemic renal injury by blocking mitochondrial fission.

Renal Impairment with Sublethal Tubular Cell Injury in a Chronic Liver Disease Mouse Model

The pathogenesis of renal impairment in chronic liver diseases (CLDs) has been primarily studied in the advanced stages of hepatic injury. Meanwhile, the pathology of renal impairment in the early phase of CLDs is poorly understood, and animal models to elucidate its mechanisms are needed. Thus, we investigated whether an existing mouse model of CLD induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) shows renal impairment in the early phase. Renal injury markers, renal histology (including immunohistochemistry for tubular injury markers and transmission electron microscopy), autophagy, and oxidative stress were studied longitudinally in DDC- and standard diet-fed BALB/c mice. Slight but significant renal dysfunction was evident in DDC-fed mice from the early phase. Meanwhile, histological examinations of the kidneys with routine light microscopy did not show definitive morphological findings, and electron microscopic analyses were required to detect limited injuries such as loss of brush border microvilli and mitochondrial deformities. Limited injuries have been recently designated as sublethal tubular cell injury. As humans with renal impairment, either with or without CLD, often show almost normal tubules, sublethal injury has been of particular interest. In this study, the injuries were associated with mitochondrial aberrations and oxidative stress, a possible mechanism for sublethal injury. Intriguingly, two defense mechanisms were associated with this injury that prevent it from progressing to apparent cell death: autophagy and single-cell extrusion with regeneration. Furthermore, the renal impairment of this model progressed to chronic kidney disease with interstitial fibrosis after long-term DDC feeding. These findings indicated that DDC induces renal impairment with sublethal tubular cell injury from the early phase, leading to chronic kidney disease. Importantly, this CLD mouse model could be useful for studying the pathophysiological mechanisms of sublethal tubular cell injury.

Effects of inhaled CO administration on acute lung injury in baboons with pneumococcal pneumonia

Inhaled carbon monoxide (CO) gas has therapeutic potential for patients with acute respiratory distress syndrome if a safe, evidence-based dosing strategy and a ventilator-compatible CO delivery system can be developed. In this study, we used a clinically relevant baboon model of Streptococcus pneumoniae pneumonia to 1) test a novel, ventilator-compatible CO delivery system; 2) establish a safe and effective CO dosing regimen; and 3) investigate the local and systemic effects of CO therapy on inflammation and acute lung injury (ALI). Animals were inoculated with S. pneumoniae (10(8)-10(9) CFU) (n = 14) or saline vehicle (n = 5); in a subset with pneumonia (n = 5), we administered low-dose, inhaled CO gas (100-300 ppm × 60-90 min) at 0, 6, 24, and/or 48 h postinoculation and serially measured blood carboxyhemoglobin (COHb) levels. We found that CO inhalation at 200 ppm for 60 min is well tolerated and achieves a COHb of 6-8% with ambient CO levels ≤ 1 ppm. The COHb level measured at 20 min predicted the 60-min COHb level by the Coburn-Forster-Kane equation with high accuracy. Animals given inhaled CO + antibiotics displayed significantly less ALI at 8 days postinoculation compared with antibiotics alone. Inhaled CO was associated with activation of mitochondrial biogenesis in the lung and with augmentation of renal antioxidative programs. These data support the feasibility of safely delivering inhaled CO gas during mechanical ventilation and provide preliminary evidence that CO may accelerate the resolution of ALI in a clinically relevant nonhuman primate pneumonia model.

Mitochondrial proteomes of porcine kidney cortex and medulla: foundation for translational proteomics

BACKGROUND

Emerging evidence has linked mitochondrial dysfunction to the pathogenesis of many renal disorders, including acute kidney injury, sepsis and even chronic kidney disease. Proteomics is a powerful tool in elucidating the role of mitochondria in renal pathologies. Since the pig is increasingly recognized as a major mammalian model for translational research, the lack of physiological proteome data of large mammals prompted us to examine renal mitochondrial proteome in porcine kidney cortex and medulla

METHODS

Kidneys were obtained from six healthy pigs. Mitochondria from cortex and medulla were isolated using differential centrifugation and proteome maps of cortical and medullar mitochondria were constructed using two-dimensional gel electrophoresis (2DE). Protein spots with significant difference between mitochondrial fraction of renal cortex and medulla were identified by mass spectrometry.

RESULTS

Proteomic analysis identified 81 protein spots. Of these spots, 41 mitochondrial proteins were statistically different between renal cortex and medulla (p < 0.05). Protein spots containing enzymes of beta oxidation, amino acid metabolism, and gluconeogenesis were predominant in kidney cortex mitochondria. Spots containing tricarboxylic acid cycle enzymes and electron transport system proteins, proteins maintaining metabolite transport and mitochondrial translation were more abundant in medullar mitochondria.

CONCLUSION

This study provides the first proteomic profile of porcine kidney cortex and medullar mitochondrial proteome. Different protein expression pattern reflects divergent functional metabolic role of mitochondria in various kidney compartments. Our study could serve as a useful reference for further porcine experiments investigating renal mitochondrial physiology under various pathological states.

MKK3 mediates inflammatory response through modulation of mitochondrial function

Mitochondria are increasingly recognized as drivers of inflammatory responses. MAP kinase kinase 3 (MKK3), a dual-specificity protein kinase, is activated in inflammation and in turn activates p38 MAP kinase signaling. Here we show that MKK3 influences mitochondrial function and acts as a critical mediator of inflammation. MKK3-deficient (MKK3(-/-)) mice and bone marrow-derived macrophages (BMDMs) secreted smaller amounts of cytokines than wild type (WT) after lipopolysaccharide (LPS) exposure. There was improved mitochondrial function, as measured by basal oxygen consumption rate, mitochondrial membrane potential, and ATP production, in MKK3(-/-) BMDMs. After LPS exposure, MKK3(-/-) BMDMs did not show a significant increase in cellular reactive oxygen species production or in mitochondrial superoxide compared to WT. Activation of two important inflammatory mediators, i.e., the nuclear translocation of NF-κB and caspase-1 activity (a key component of the inflammasome), was lower in MKK3(-/-) BMDMs. p38 and JNK activation was lower in MKK3(-/-) BMDMs compared to WT after exposure to LPS. Knockdown of MKK3 by siRNA in wild-type BMDMs improved mitochondrial membrane potential, reduced LPS-induced caspase-1 activation, and attenuated cytokine secretion. Our studies establish MKK3 as a regulator of mitochondrial function and inflammatory responses to LPS and suggest that MKK3 may be a therapeutic target in inflammatory disorders such as sepsis.

Low-dose carvedilol protects against acute septic renal injury in rats during the early and late phases

Recent findings from septic acute renal injury studies have implicated the mitochondrion as an important factor in kidney injury, and that increased sympathetic nerve activity may contribute to the induction of organ failure. This study investigated the impact of a nondepressor dose of carvedilol, which is a beta-adrenoreceptor antagonist with antioxidant activity, on septic renal injury induced in rats with cecal ligation and puncture (CLP). Three groups of rats were studied. The first group was the sham-operated control. The other 2 groups of rats underwent CLP, and were administered either the vehicle or carvedilol (2.0 mg/kg body mass, by intraperitoneal (i.p.) injection, daily for 2 days as well as 30 min prior to CLP). Kidney function, inflammatory parameters, mitochondrial function, and renal perfusion pressure (RPP) were investigated at 6 and 18 h after CLP. Carvedilol did not significantly induce hypotension, and it significantly improved RPP and renal dysfunction induced with CLP, together with significant reductions in serum levels of interleukin 6 and tumor necrosis factor-alpha. Septic kidney injury mediated increased levels of malondialdehyde and protein carbonyls. Carvedilol also attenuated the decrease in kidney mitochondrial glutathione and nicotinamide adenine dinucleotide phosphate dehydrogenase. Further, intracellular renal edema and inflammation induced with CLP were reduced with carvedilol. These findings suggest renoprotective effects of carvedilol in sepsis.

Hypertension-related, calcium-regulated gene (HCaRG/COMMD5) and kidney diseases: HCaRG accelerates tubular repair

Hypertension is a risk factor for renal impairment. While treatment of hypertension provides significant renal protection, there is still an unmet need requiring further exploration of additional pathogenetic mechanisms. We have found that the hypertension-related, calcium-regulated gene (HCaRG/COMMD5) is involved in renal repair. HCaRG is a small intracellular protein of 225 amino acids and its gene expression is negatively regulated by extracellular calcium concentrations. HCaRG is mostly expressed in the kidneys, with higher levels found in the spontaneously hypertensive rat than in normotensive rats. In an acute kidney injury model, HCaRG expression decreases immediately after injury but increases above baseline during the repair phase. In cell cultures, HCaRG has been shown to facilitate differentiation and to inhibit cell proliferation via p21 transactivation through the p53-independent signaling pathway. Induction of p21 independently of p53 is also observed in transgenic mice overexpressing HCaRG during the repair phase after ischemia/reperfusion injury, resulting in their improved renal function and survival with rapid re-differentiation of proximal tubular epithelial cells. In addition, transgenic mice recover rapidly from the inflammatory burst most likely as a result of maintenance of the tubular epithelial barrier. Recent studies indicate that facilitating re-differentiation and cell cycle regulation in injured renal proximal tubules might be important functions of HCaRG. We have proposed that HCaRG is a component of differential genetic susceptibility to renal impairment in response to hypertension.