The role of polyamine metabolism in cellular function and physiology.

Polyamines are molecules with multiple amino groups that are essential for cellular function. The major polyamines are putrescine, spermidine, spermine, and cadaverine. Polyamines are important for posttranscriptional regulation, autophagy, programmed cell death, proliferation, redox homeostasis, and ion channel function; their levels are tightly controlled. High levels of polyamines are associated with proliferative pathologies such as cancer, while low polyamine levels are observed in aging, and elevated polyamine turnover enhances oxidative stress. Polyamine metabolism is implicated in a variety of pathophysiological processes in the nervous, immune, and cardiovascular systems. Currently, manipulating polyamine levels is under investigation as a potential preventive treatment in several pathologies, including aging, ischemia/reperfusion injury, pulmonary hypertension, and cancer. Although polyamines have been implicated in a plethora of intracellular mechanisms, our understanding of these processes remains incomplete and is a topic of ongoing investigations. Here, we discuss the regulation and cellular functions of polyamines, their role in physiology and pathology, and emphasize the current gaps in knowledge and potential future research directions.

Transcriptomic changes in glomeruli in response to a high salt challenge in the Dahl SS rat.

Salt sensitivity impacts a significant portion of the population and is an important contributor to the development of chronic kidney disease. One of the significant early predictors of salt-induced damage is albuminuria, which reflects the deterioration of the renal filtration barrier: the glomerulus. Despite significant research efforts, there is still a gap in knowledge regarding the molecular mechanisms and signaling networks contributing to instigating and/or perpetuating salt-induced glomerular injury. To address this gap, we used 8-wk-old male Dahl salt-sensitive rats fed a normal-salt diet (0.4% NaCl) or challenged with a high-salt diet (4% NaCl) for 3 wk. At the end of the protocol, a pure fraction of renal glomeruli obtained by differential sieving was used for next-generation RNA sequencing and comprehensive semi-automatic transcriptomic data analyses, which revealed 149 differentially expressed genes (107 and 42 genes were downregulated and upregulated, respectively). Furthermore, a combination of predictive gene correlation networks and computational bioinformatic analyses revealed pathways impacted by a high salt dietary challenge, including renal metabolism, mitochondrial function, apoptotic signaling and fibrosis, cell cycle, inflammatory and immune responses, circadian clock, cytoskeletal organization, G protein-coupled receptor signaling, and calcium transport. In conclusion, we report here novel transcriptomic interactions and corresponding predicted pathways affecting glomeruli under salt-induced stress.NEW & NOTEWORTHY 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.

Cilia-deficient renal tubule cells are primed for injury with mitochondrial defects and aberrant tryptophan metabolism.

The exocyst and Ift88 are necessary for primary ciliogenesis. Overexpression of Exoc5 (OE), a central exocyst component, resulted in longer cilia and enhanced injury recovery. Mitochondria are involved in acute kidney injury (AKI). To investigate cilia and mitochondria, basal respiration and mitochondrial maximal and spare respiratory capacity were measured in Exoc5 OE, Exoc5 knockdown (KD), Exoc5 ciliary targeting sequence mutant (CTS-mut), control Madin-Darby canine kidney (MDCK), Ift88 knockout (KO), and Ift88 rescue cells. In Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells, these parameters were decreased. In Exoc5 OE and Ift88 rescue cells they were increased. Reactive oxygen species were higher in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells compared with Exoc5 OE, control, and Ift88 rescue cells. By electron microscopy, mitochondria appeared abnormal in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells. A metabolomics screen of control, Exoc5 KD, Exoc5 CTS-mut, Exoc5 OE, Ift88 KO, and Ift88 rescue cells showed a marked increase in tryptophan levels in Exoc5 CTS-mut (113-fold) and Exoc5 KD (58-fold) compared with control cells. A 21% increase was seen in Ift88 KO compared with rescue cells. In Exoc5 OE compared with control cells, tryptophan was decreased 59%. To determine the effects of ciliary loss on AKI, we generated proximal tubule-specific Exoc5 and Ift88 KO mice. These mice had loss of primary cilia, decreased mitochondrial ATP synthase, and increased tryptophan in proximal tubules with greater injury following ischemia-reperfusion. These data indicate that cilia-deficient renal tubule cells are primed for injury with mitochondrial defects in tryptophan metabolism.NEW & NOTEWORTHY Mitochondria are centrally involved in acute kidney injury (AKI). Here, we show that cilia-deficient renal tubule cells both in vitro in cell culture and in vivo in mice are primed for injury with mitochondrial defects and aberrant tryptophan metabolism. These data suggest therapeutic strategies such as enhancing ciliogenesis or improving mitochondrial function to protect patients at risk for AKI.

Renal histaminergic system and acute effects of histamine receptor 2 blockade on renal damage in the Dahl salt-sensitive rat.

Histamine is involved in the regulation of immune response, vasodilation, neurotransmission, and gastric acid secretion. Although elevated histamine levels and increased expression of histamine metabolizing enzymes have been reported in renal disease, there is a gap in knowledge regarding the mechanisms of histamine-related pathways in the kidney. We report here that all four histamine receptors as well as enzymes responsible for the metabolism of histamine are expressed in human and rat kidney tissues. In this study, we hypothesized that the histaminergic system plays a role in salt-induced kidney damage in the Dahl salt-sensitive (DSS) rat, a model characterized with inflammation-driven renal lesions. To induce renal damage related to salt sensitivity, DSS rats were challenged with 21 days of a high-salt diet (4% NaCl); normal-salt diet (0.4% NaCl)-fed rats were used as a control. We observed lower histamine decarboxylase and higher histamine N-methyltransferase levels in high-salt diet-fed rats, indicative of a shift in histaminergic tone; metabolomics showed higher histamine and histidine levels in the kidneys of high-salt diet-fed rats, whereas plasma levels for both compounds were lower. Acute systemic inhibition of histamine receptor 2 in the DSS rat revealed that it lowered vasopressin receptor 2 in the kidney. In summary, we established here the existence of the local histaminergic system, revealed a shift in the renal histamine balance during salt-induced kidney damage, and provided evidence that blockage of histamine receptor 2 in the DSS rat affects water balance and urine concentrating mechanisms.NEW & NOTEWORTHY Histamine is a nitrogenous compound crucial for the inflammatory response. The knowledge regarding the renal effects of histamine is very limited. We showed that renal epithelia exhibit expression of the components of the histaminergic system. Furthermore, we revealed that there was a shift in the histaminergic tone in salt-sensitive rats when they were challenged with a high-salt diet. These data support the notion that histamine plays a role in renal epithelial physiological and pathophysiological functions.

ß-Arrestin pathway activation by selective ATR1 agonism promotes calcium influx in podocytes, leading to glomerular damage.

Angiotensin receptor blockers (ARBs) are the first-line treatment for hypertension; they act by inhibiting signaling through the angiotensin 1 receptor (AT1R). Recently, a novel biased AT1R agonist, TRV120027 (TRV), which selectively activates the ß-arrestin cascade and blocks the G-protein-coupled receptor pathway has been proposed as a potential blood pressure medication. Here, we explored the effects of TRV and associated ß-arrestin signaling in podocytes, essential cells of the kidney filter. We used human podocyte cell lines to determine ß-arrestin's involvement in calcium signaling and cytoskeletal reorganization and Dahl SS rats to investigate the chronic effects of TRV administration on glomerular health. Our experiments indicate that the TRV-activated ß-arrestin pathway promotes the rapid elevation of intracellular Ca2+ in a dose-dependent manner. Interestingly, the amplitude of ß-arrestin-mediated Ca2+ influx was significantly higher than the response to similar Ang II concentrations. Single-channel analyses show rapid activation of transient receptor potential canonical (TRPC) channels following acute TRV application. Furthermore, the pharmacological blockade of TRPC6 significantly attenuated the ß-arrestin-mediated Ca2+ influx. Additionally, prolonged activation of the ß-arrestin pathway in podocytes resulted in pathological actin cytoskeleton rearrangements, higher apoptotic cell markers, and augmented glomerular damage. TRV-activated ß-arrestin signaling in podocytes may promote TRPC6 channel-mediated Ca2+ influx, foot process effacement, and apoptosis, possibly leading to severe defects in glomerular filtration barrier integrity and kidney health. Under these circumstances, the potential therapeutic application of TRV for hypertension treatment requires further investigation to assess the balance of the benefits versus possible deleterious effects and off-target damage.

Functional role of histamine receptors in the renal cortical collecting duct cells.

Histamine is an important immunomodulator, as well as a regulator of allergic inflammation, gastric acid secretion, and neurotransmission. Although substantial histamine level has been reported in the kidney, renal pathological and physiological effects of this compound have not been clearly defined. The goal of this study was to provide insight into the role of histamine-related pathways in the kidney, with emphasis on the collecting duct (CD), a distal part of the nephron important for the regulation of blood pressure. We report that all four histamine receptors (HRs) as well as enzymes responsible for histamine metabolism and synthesis are expressed in cultured mouse mpkCCDcl4 cells, and histamine evokes a dose-dependent transient increase in intracellular Ca2+ in these cells. Furthermore, we observed a dose-dependent increase in cAMP in the CD cells in response to histamine. Short-circuit current studies aimed at measuring Na+ reabsorption via ENaC (epithelial Na+ channel) demonstrated inhibition of ENaC-mediated currents by histamine after a 4-h incubation, and single-channel patch-clamp analysis revealed similar ENaC open probability before and after acute histamine application. The long-term (4 h) effect on ENaC was corroborated in immunocytochemistry and qPCR, which showed a decrease in protein and gene expression for αENaC upon histamine treatment. In summary, our data highlight the functional importance of HRs in the CD cells and suggest potential implications of histamine in inflammation-related renal conditions. Further research is required to discern the molecular pathways downstream of HRs and assess the role of specific receptors in renal pathophysiology.

Practical notes on popular statistical tests in renal physiology.

Competent statistical analysis is essential to maintain rigor and reproducibility in physiological research. Unfortunately, the benefits offered by statistics are often negated by misuse or inadequate reporting of statistical methods. To address the need for improved quality of statistical analysis in papers, the American Physiological Society released guidelines for reporting statistics in journals published by the society. The guidelines reinforce high standards for the presentation of statistical data in physiology but focus on the conceptual challenges and, thus, may be of limited use to an unprepared reader. Experimental scientists working in the renal field may benefit from putting the existing guidelines in a practical context. This paper discusses the application of widespread hypothesis tests in a confirmatory study. We simulated pharmacological experiments assessing intracellular calcium in cultured renal cells and kidney function at the systemic level to review best practices for data analysis, graphical presentation, and reporting. Such experiments are ubiquitously used in renal physiology and could be easily translated to other practical applications to fit the reader's specific needs. We provide step-by-step guidelines for using the most common types of t tests and ANOVA and discuss typical mistakes associated with them. We also briefly consider normality tests, exclusion criteria, and identification of technical and experimental replicates. This review is supposed to help the reader analyze, illustrate, and report the findings correctly and will hopefully serve as a gauge for a level of design complexity when it might be time to consult a biostatistician.

FGF21 prevents low-protein diet-induced renal inflammation in aged mice.

Low-protein (LP) diets extend lifespan through a comprehensive improvement in metabolic health across multiple tissues and organs. Many of these metabolic responses to protein restriction are secondary to transcriptional activation and release of FGF21 from the liver. However, the effects of an LP diet on the kidney in the context of aging has not been examined. Therefore, the goal of the current study was to investigate the impact of chronic consumption of an LP diet on the kidney in aging mice lacking FGF21. Wild-type (WT; C57BL/6J) and FGF21 knockout (KO) mice were fed a normal protein diet (20% casein) or an LP (5% casein) diet ad libitum from 3 to 22 mo of age. The LP diet led to a decrease in kidney weight and urinary albumin-to-creatinine ratio in both WT and FGF21 KO mice. Although the LP diet produced only mild fibrosis and infiltration of leukocytes in WT kidneys, the effects were significantly exacerbated by the absence of FGF21. Accordingly, transcriptomic analysis showed that inflammation-related pathways were significantly enriched and upregulated in response to LP diet in FGF21 KO mice but not WT mice. Collectively, these data demonstrate that the LP diet negatively affected the kidney during aging, but in the absence of FGF21, the LP diet-induced renal damage and inflammation were significantly worse, indicating a protective role of FGF21 in the kidney.NEW & NOTEWORTHY 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.

Chronic Porphyromonas gingivalis lipopolysaccharide induces adverse myocardial infarction wound healing through activation of CD8+ T cells.

Oral and gum health have long been associated with incidence and outcomes of cardiovascular disease. Periodontal disease increases myocardial infarction (MI) mortality by sevenfold through mechanisms that are not fully understood. The goal of this study was to evaluate whether lipopolysaccharide (LPS) from a periodontal pathogen accelerates inflammation after MI through memory T-cell activation. We compared four groups [no MI, chronic LPS, day 1 after MI, and day 1 after MI with chronic LPS (LPS + MI); n = 68 mice] using the mouse heart attack research tool 1.0 database and tissue bank coupled with new analyses and experiments. LPS + MI increased total CD8+ T cells in the left ventricle versus the other groups (P < 0.05 vs. all). Memory CD8+ T cells (CD44 + CD27+) were 10-fold greater in LPS + MI than in MI alone (P = 0.02). Interleukin (IL)-4 stimulated splenic CD8+ T cells away from an effector phenotype and toward a memory phenotype, inducing secretion of factors associated with the Wnt/ß-catenin signaling that promoted monocyte migration and decreased viability. To dissect the effect of CD8+ T cells after MI, we administered a major histocompatibility complex-I-blocking antibody starting 7 days before MI, which prevented effector CD8+ T-cell activation without affecting the memory response. The reduction in effector cells diminished infarct wall thinning but had no effect on macrophage numbers or MertK expression. LPS + MI + IgG attenuated macrophages within the infarct without effecting CD8+ T cells, suggesting these two processes were independent. Overall, our data indicate that effector and memory CD8+ T cells at post-MI day 1 are amplified by chronic LPS to potentially promote infarct wall thinning.NEW & NOTEWORTHY Although there is a well-documented link between periodontal disease and heart health, the mechanisms are unclear. Our study indicates that in response to circulating periodontal endotoxins, memory CD8+ T cells are activated, resulting in an acceleration of macrophage-mediated inflammation after MI. Blocking activation of effector CD8+ T cells had no effect on the macrophage numbers or wall thinning at post-MI day 1, indicating that this response was likely due in part to memory CD8+ T cells.

Recent advances in understanding ion transport mechanisms in polycystic kidney disease.

This review focuses on the most recent advances in the understanding of the electrolyte transport-related mechanisms important for the development of severe inherited renal disorders, autosomal dominant (AD) and recessive (AR) forms of polycystic kidney disease (PKD). We provide here a basic overview of the origins and clinical aspects of ARPKD and ADPKD and discuss the implications of electrolyte transport in cystogenesis. Special attention is devoted to intracellular calcium handling by the cystic cells, with a focus on polycystins and fibrocystin, as well as other calcium level regulators, such as transient receptor potential vanilloid type 4 (TRPV4) channels, ciliary machinery, and purinergic receptor remodeling. Sodium transport is reviewed with a focus on the epithelial sodium channel (ENaC), and the role of chloride-dependent fluid secretion in cystic fluid accumulation is discussed. In addition, we highlight the emerging promising concepts in the field, such as potassium transport, and suggest some new avenues for research related to electrolyte handling.

NOX4-dependent regulation of ENaC in hypertension and diabetic kidney disease.

NADPH oxidase 4 (NOX4) is the most abundant NOX isoform in the kidney; however, its importance for renal function has only recently emerged. The NOX4-dependent pathway regulates many factors essential for proper sodium handling in the distal nephron. However, the functional significance of this pathway in the control of sodium reabsorption during the initiation of chronic kidney disease is not established. The goal of this study was to test Nox4-dependent ENaC regulation in two models: SS hypertension and STZ-induced type 1 diabetes. First, we showed that genetic ablation of Nox4 in Dahl salt-sensitive (SS) rat attenuated a high-salt (HS)-induced increase in epithelial Na+ channel (ENaC) activity in the cortical collecting duct. We also found that H2 O2 upregulated ENaC activity, and H2 O2 production was reduced in both the renal cortex and medulla in SSNox4-/- rats fed an HS diet. Second, in the streptozotocin model of hyperglycemia-induced renal injury ENaC activity in hyperglycemic animals was elevated in SS but not SSNox4-/- rats. NaCl cotransporter (NCC) expression was increased compared to healthy controls, while expression values between SS and SSNox4-/- groups were similar. These data emphasize a critical contribution of the NOX4-mediated pathway in maladaptive upregulation of ENaC-mediated sodium reabsorption in the distal nephron in the conditions of HS- and hyperglycemia-induced kidney injury.

Inhibition of neprilysin with sacubitril without RAS blockage aggravates renal disease in Dahl SS rats.

Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 µg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 µg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.

The exocyst acting through the primary cilium is necessary for renal ciliogenesis, cystogenesis, and tubulogenesis.

The exocyst is a highly conserved protein complex found in most eukaryotic cells and is associated with many functions, including protein translocation in the endoplasmic reticulum, vesicular basolateral targeting, and ciliogenesis in the kidney. To investigate the exocyst functions, here we exchanged proline for alanine in the highly conserved VXPX ciliary targeting motif of EXOC5 (exocyst complex component 5), a central exocyst gene/protein, and generated stable EXOC5 ciliary targeting sequence-mutated (EXOC5CTS-m) Madin-Darby canine kidney (MDCK) cells. The EXOC5CTS-m protein was stable and could bind other members of the exocyst complex. Culturing stable control, EXOC5-overexpressing (OE), Exoc5-knockdown (KD), and EXOC5CTS-m MDCK cells on Transwell filters, we found that primary ciliogenesis is increased in EXOC5 OE cells and inhibited in Exoc5-KD and EXOC5CTS-m cells. Growing cells in collagen gels until the cyst stage, we noted that EXOC5-OE cells form mature cysts with single lumens more rapidly than control cysts, whereas Exoc5-KD and EXOC5CTS-m MDCK cells failed to form mature cysts. Adding hepatocyte growth factor to induce tubulogenesis, we observed that EXOC5-OE cell cysts form tubules more efficiently than control MDCK cell cysts, EXOC5CTS-m MDCK cell cysts form significantly fewer tubules than control cell cysts, and Exoc5-KD cysts did not undergo tubulogenesis. Finally, we show that EXOC5 mRNA almost completely rescues the ciliary phenotypes in exoc5-mutant zebrafish, unlike the EXOC5CTS-m mRNA, which could not efficiently rescue the phenotypes. Taken together, these results indicate that the exocyst, acting through the primary cilium, is necessary for renal ciliogenesis, cystogenesis, and tubulogenesis.

Comprehensive assessment of mitochondrial respiratory function in freshly isolated nephron segments.

Changes in mitochondrial function are central to many forms of kidney disease, including acute injury, diabetic nephropathy, hypertension, and chronic kidney diseases. As such, there is an increasing need for reliable and fast methods for assessing mitochondrial respiratory function in renal cells. Despite being indispensable for many mechanistic studies, cultured cells or isolated mitochondria, however, often do not recapitulate in vivo or close to in vivo situations. Cultured and/or immortalized cells often change their bioenergetic profile and phenotype compared with in vivo or ex vivo situations, and isolated mitochondria are simply removed from their cellular milieu. This is especially important for extremely complex organs such as the kidney. Here, we report the development and validation of a new approach for the rapid assessment of mitochondrial oxygen consumption on freshly isolated glomeruli or proximal tubular fragments using Agilent SeaHorse XFe24 and XF96 Extracellular Flux Analyzers. We validated the technique in several healthy and diseased rodent models: the C57BL/6J mouse, the diabetic db/db mouse and matching db/+ control mouse, and the Dahl salt-sensitive rat. We compared the data to respiration from isolated mitochondria. The method can be adapted and used for the rapid assessment of mitochondrial oxygen consumption from any rodent model of the investigator's choice. The isolation methods presented here ensure viable and functional proximal tubular fragments and glomeruli, with a preserved cellular environment for studying mitochondrial function within the context of their surroundings and interactions.

Sex differences in renal mitochondrial function: a hormone-gous opportunity for research.

Sex differences (biological distinctions between males and females) present a complex interplay of genetic, developmental, biological, and environmental factors. More and more studies are shedding light on the importance of sex differences in normal physiology and susceptibility to cancer, cardiovascular and renal conditions, and neurodegenerative diseases. This mini-review is devoted to the role of sex dimorphisms in renal function, with a focus on the distinctions between male and female mitochondria. Here, we cover the aspects of renal mitochondrial bioenergetics where sex differences have been reported to date, for instance, biogenesis, reactive oxygen species production, and oxidative stress. Special attention is devoted to the effects of sex hormones, such as estrogen and testosterone, on mitochondrial bioenergetics in the kidney in physiology and pathophysiology.

Differential effects of low-dose sacubitril and/or valsartan on renal disease in salt-sensitive hypertension.

Diuretics and renin-angiotensin system blockers are often insufficient to control the blood pressure (BP) in salt-sensitive (SS) subjects. Abundant data support the proposal that the level of atrial natriuretic peptide may correlate with the pathogenesis of SS hypertension. We hypothesized here that increasing atrial natriuretic peptide levels with sacubitril, combined with renin-angiotensin system blockage by valsartan, can be beneficial for alleviation of renal damage in a model of SS hypertension, the Dahl SS rat. To induce a BP increase, rats were challenged with a high-salt 4% NaCl diet for 21 days, and chronic administration of vehicle or low-dose sacubitril and/or valsartan (75 µg/day each) was performed. Urine flow, Na+ excretion, and water consumption were increased on the high-salt diet compared with the starting point (0.4% NaCl) in all groups but remained similar among the groups at the end of the protocol. Upon salt challenge, we observed a mild decrease in systolic BP and urinary neutrophil gelatinase-associated lipocalin levels (indicative of alleviated tubular damage) in the valsartan-treated groups. Sacubitril, as well as sacubitril/valsartan, attenuated the glomerular filtration rate decline induced by salt. Alleviation of protein cast formation and lower renal medullary fibrosis were observed in the sacubitril/valsartan- and valsartan-treated groups, but not when sacubitril alone was administered. Interestingly, proteinuria was mildly mitigated only in rats that received sacubitril/valsartan. Further studies of the effects of sacubitril/valsartan in the setting of SS hypertension, perhaps involving a higher dose of the drug, are warranted to determine if it can interfere with the progression of the disease.

Regulation of mitochondria function by natriuretic peptides.

Natriuretic peptides (NPs) are well known to promote renal Na+ excretion, counteracting the effects of the renin-angiotensin-aldosterone system. Thus, NPs serve as a key component in the maintenance of blood pressure, influencing fluid retention capabilities via osmoregulation. Recently, NPs have been shown to affect lipolysis and enhance lipid oxidation and mitochondrial respiration. Here, we provide an overview of current knowledge about the relationship between NPs and mitochondria-mediated processes such as reactive oxygen species production, Ca2+ signaling, and apoptosis. Establishing a clear physiological and mechanistic connection between NPs and mitochondria in the cardiovascular system will open new avenues of research aimed at understanding and potentially using it as a therapeutic target from a completely new angle.

Progression of diabetic kidney disease in T2DN rats.

Diabetic kidney disease (DKD) is one of the leading pathological causes of decreased renal function and progression to end-stage kidney failure. To explore and characterize age-related changes in DKD and associated glomerular damage, we used a rat model of type 2 diabetic nephropathy (T2DN) at 12 wk and older than 48 wk. We compared their disease progression with control nondiabetic Wistar and diabetic Goto-Kakizaki (GK) rats. During the early stages of DKD, T2DN and GK animals revealed significant increases in blood glucose and kidney-to-body weight ratio. Both diabetic groups had significantly altered renin-angiotensin-aldosterone system function. Thereafter, during the later stages of disease progression, T2DN rats demonstrated a remarkable increase in renal damage compared with GK and Wistar rats, as indicated by renal hypertrophy, polyuria accompanied by a decrease in urine osmolarity, high cholesterol, a significant prevalence of medullary protein casts, and severe forms of glomerular injury. Urinary nephrin shedding indicated loss of the glomerular slit diaphragm, which also correlates with the dramatic elevation in albuminuria and loss of podocin staining in aged T2DN rats. Furthermore, we used scanning ion microscopy topographical analyses to detect and quantify the pathological remodeling in podocyte foot projections of isolated glomeruli from T2DN animals. In summary, T2DN rats developed renal and physiological abnormalities similar to clinical observations in human patients with DKD, including progressive glomerular damage and a significant decrease in renin-angiotensin-aldosterone system plasma levels, indicating these rats are an excellent model for studying the progression of renal damage in type 2 DKD.

Adaptive immunity-driven inflammation and cardiovascular disease.

The adaptive immune response has recently emerged as an important factor in a wide variety of cardiovascular disorders including atherosclerosis, hypertension, cardiac remodeling, and heart failure; however, its role is not fully understood. Since an assortment of innate responsive cells, e.g., neutrophils and monocytes/macrophages, coordinate with adaptive immunity, e.g., T cells, dendritic cells, and B cells, the temporal response and descriptions pertinent to the cellular phenotype and inflammation processes, in general, need additional investigation, clarification, and consensus particularly in cardiovascular disease. This Perspectives article reviews the contributions of 15 articles (including 7 reviews) published in the American Journal of Physiology-Heart and Circulatory Physiology in response to the Call for Papers: Adaptive Immunity in Cardiovascular Disease. Here, we summarize the crucial reported findings at the cardiac, vascular, immune, and molecular levels and discuss the translational feasibility and benefits of future prospective research into the adaptive immune response. Readers are encouraged to evaluate the data and learn from this collection of novel studies.

CD8+ T-cells negatively regulate inflammation post-myocardial infarction.

The adaptive immune response is key for cardiac wound healing post-myocardial infarction (MI) despite low T-cell numbers. We hypothesized that CD8+ T-cells regulate the inflammatory response, leading to decreased survival and cardiac function post-MI. We performed permanent occlusion of the left anterior descending coronary artery on C57BL/6J and CD8atm1mak mice (deficient in functional CD8+ T-cells). CD8atm1mak mice had increased survival at 7 days post-MI compared with that of the wild-type (WT) and improved cardiac physiology at day 7 post-MI. Despite having less mortality, 100% of the CD8atm1mak group died because of cardiac rupture compared with only 33% of the WT. Picrosirius red staining and collagen immunoblotting indicated an acceleration of fibrosis in the infarct area as well as remote area in the CD8atm1mak mice; however, this increase was due to elevated soluble collagen implicating poor scar formation. Plasma and tissue inflammation were exacerbated as indicated by higher levels of Cxcl1, Ccl11, matrix metalloproteinase (MMP)-2, and MMP-9. Immunohistochemistry and flow cytometry indicated that the CD8atm1mak group had augmented numbers of neutrophils and macrophages at post-MI day 3 and increased mast cell markers at post-MI day 7. Cleavage of tyrosine-protein kinase MER was increased in the CD8atm1mak mice, resulting in delayed removal of necrotic tissue. In conclusion, despite having improved cardiac physiology and overall survival, CD8atm1mak mice had increased innate inflammation and poor scar formation, leading to higher incidence of cardiac rupture. Our data suggest that the role of CD8+ T-cells in post-MI recovery may be both beneficial and detrimental to cardiac remodeling and is mediated via a cell-specific mechanism.NEW & NOTEWORTHY We identified new mechanisms implicating CD8+ T-cells as regulators of the post-myocardial infarction (MI) wound healing process. Mice without functional CD8+ T-cells had improved cardiac physiology and less mortality 7 days post MI compared with wild-type animals. Despite having better overall survival, animals lacking functional CD8+ T-cells had delayed removal of necrotic tissue, leading to poor scar formation and increased cardiac rupture, suggesting that CD8+ T-cells play a dual role in the cardiac remodeling process.