Renal kallikrein-kinin system damage and salt sensitivity: insights from experimental models

New integrative approaches to discovery of pathophysiological mechanisms triggered by night shift work

Synchronization to periodic cues such as food/water availability and light/dark cycles is crucial for living organisms' homeostasis. Both factors have been heavily influenced by human activity, with artificial light at night (ALAN) being an evolutionary challenge imposed over roughly the last century. Evidence from studies in humans and animal models shows that overt circadian misalignment, such as that imposed to about 20% of the workforce by night shift work (NSW), negatively impinges on the internal temporal order of endocrinology, physiology, metabolism, and behavior. Moreover, NSW is often associated to mistimed feeding, with both unnatural behaviors being known to increase the risk of chronic diseases, such as eating disorders, overweight, obesity, cardiovascular, metabolic (particularly type 2 diabetes mellitus) and gastrointestinal disorders, some types of cancer, as well as mental disease including sleep disturbances, cognitive disorders, and depression. Regarding deleterious effects of ALAN on reproduction, increased risk of miscarriage, preterm delivery and low birth weight have been reported in shift-worker women. These mounting lines of evidence prompt further efforts to advance our understanding of the effects of long-term NSW on health. Emerging data suggest that NSW with or without mistimed feeding modify gene expression and functional readouts in different tissues/organs, which seem to translate into persistent cardiometabolic and endocrine dysfunction. However, this research avenue still faces multiple challenges, such as functional characterization of new experimental models more closely resembling human long-term NSW and mistimed feeding in males versus females; studying further target organs; identifying molecular changes by means of deep multi-omics analyses; and exploring biomarkers of NSW with translational medicine potential. Using high-throughput and systems biology is a relatively new approach to study NSW, aimed to generate experiments addressing new biological factors, pathways, and mechanisms, going beyond the boundaries of the circadian clock molecular machinery.

Fetal Programming of Renal Dysfunction and High Blood Pressure by Chronodisruption

Adverse prenatal conditions are known to impose significant trade-offs impinging on health and disease balance during adult life. Among several deleterious factors associated with complicated pregnancy, alteration of the gestational photoperiod remains largely unknown. Previously, we reported that prenatal manipulation of the photoperiod has adverse effects on the mother, fetus, and adult offspring; including cardiac hypertrophy. Here, we investigated whether chronic photoperiod shifting (CPS) during gestation may program adult renal function and blood pressure regulation. To this end, pregnant rats were subjected to CPS throughout pregnancy to evaluate the renal effects on the fetus and adult offspring. In the kidney at 18 days of gestation, both clock and clock-controlled gene expression did not display a daily pattern, although there were recurrent weaves of transcriptional activity along the 24 h in the control group. Using DNA microarray, significant differential expression was found for 1,703 transcripts in CPS relative to control fetal kidney (835 up-regulated and 868 down-regulated). Functional genomics assessment revealed alteration of diverse gene networks in the CPS fetal kidney, including regulation of transcription, aldosterone-regulated Na+ reabsorption and connective tissue differentiation. In adult offspring at 90 days of age, circulating proinflammatory cytokines IL-1β and IL-6 were increased under CPS conditions. In these individuals, CPS did not modify kidney clock gene expression but had effects on different genes with specific functions in the nephron. Next, we evaluated several renal markers and the response of blood pressure to 4%NaCl in the diet for 4 weeks (i.e., at 150 days of age). CPS animals displayed elevated systolic blood pressure in basal conditions that remained elevated in response to 4%NaCl, relative to control conditions. At this age, CPS modified the expression of Nhe3, Ncc, Atp1a1, Nr3c1 (glucocorticoid receptor), and Nr3c2 (mineralocorticoid receptor); while Nkcc, Col3A1, and Opn were modified in the CPS 4%+NaCl group. Furthermore, CPS decreased protein expression of Kallikrein and COX-2, both involved in sodium handling. In conclusion, gestational chronodisruption programs kidney dysfunction at different levels, conceivably underlying the prehypertensive phenotype observed in the adult CPS offspring.

Up-regulation of the kinin B2 receptor pathway modulates the TGF-β/Smad signaling cascade to reduce renal fibrosis induced by albumin

The presence of high protein levels in the glomerular filtrate plays an important role in renal fibrosis, a disorder that justifies the use of animal models of experimental proteinuria. Such models have proved useful as tools in the study of the pathogenesis of chronic, progressive renal disease. Since bradykinin and the kinin B2 receptor (B2R) belong to a renoprotective system with mechanisms still unclarified, we investigated its anti-fibrotic role in the in vivo rat model of overload proteinuria. Upon up-regulating the kinin system by a high potassium diet we observed reduction of tubulointerstitial fibrosis, decreased renal expression of α-smooth muscle actin (α-SMA) and vimentin, reduced Smad3 phosphorylation and increase of Smad7. These cellular and molecular effects were reversed by HOE-140, a specific B2R antagonist. In vitro experiments, performed on a cell line of proximal tubular epithelial cells, showed that high concentrations of albumin induced expression of mesenchymal biomarkers, in concomitance with increases in TGF-β1 mRNA and its functionally active peptide, TGF-β1. Stimulation of the tubule cells by bradykinin inhibited the albumin-induced changes, namely α-SMA and vimentin were reduced, and cytokeratin recovered together with increase in Smad7 levels and decrease in type II TGF-β1 receptor, TGF-β1 mRNA and its active fragment. The protective changes produced by bradykinin in vitro were blocked by HOE-140. The development of stable bradykinin analogues and/or up-regulation of the B2R signaling pathway may prove value in the management of chronic renal fibrosis in progressive proteinuric renal diseases.

Association of functional kallikrein-1 promoter polymorphisms and acute kidney injury: a case-control and longitudinal cohort study

BACKGROUND

Kallikrein-1 (KLK1) is a highly conserved serine protease that is expressed in the kidney and involved in blood pressure regulation. The activity of this enzyme is diminished in acute kidney injury (AKI).

METHODS

We first evaluated the potential role of functional multiallelic KLK1 promoter gene polymorphisms in a case-control study of 481 subjects (214 hospitalized patients with AKI of mixed causes and 267 healthy subjects). The complex, multiallelic G/C-rich repeat region of the proximal KLK1 promoter was determined by direct Sanger/capillary resequencing.

RESULTS

16 alleles were identified in a complex, polymorphic G/C-rich region of the KLK1 proximal promoter; 5 of these alleles (F, G, H, I, and K) were associated with development of AKI. Alleles I and G were classified as risk-alleles (unadjusted OR 1.86; 95% CI 1.23, 2.81; p = 0.003), whereas alleles F, H, and K were classified as protective-alleles (unadjusted OR 0.32; 95% CI 0.22, 0.46; p < 0.001) according to their directional association with development of AKI. After adjustment for sex, race, preexisting chronic kidney disease and APACHE II score, the KLK1 risk-allele (I or G) carrier state was associated with the composite of ≥2-fold increase in serum creatinine, oliguria, or dialysis requirement (adjusted OR 2.71; 95% CI 1.14, 6.44; p = 0.02). The KLK1 risk-allele carrier state was also marginally associated with the composite of ≥2-fold increase in serum creatinine, oliguria, dialysis requirement, or in-hospital death (adjusted OR 2.33; 95% CI 0.98, 5.52; p = 0.06).

CONCLUSIONS

KLK1 promoter polymorphisms are associated with development of AKI and adverse outcomes. Further studies are needed to validate these findings.

Expression of calponin in periglomerular myofibroblasts of rat kidney with experimental chronic injuries

Our previous research demonstrated that calponin-immunoreactivity was localized in myofibroblasts of the periglomerular region of human kidney specimens obtained at the time of transplantation from organ recipients. In the present study we examined calponin expression in two chronic nephropathy models, puromycin aminonucleoside (PAN) nephropathy and subtotal nephrectomy (SNx), to investigate the role of calponin in chronic renal injury. Male Sprague-Dawley rats were used, and both nephropathy models were established at 1, 2, 4, and 8 weeks after surgery. There were no periglomerular calponin-positive cells in sham, PAN 1 and 2 week, and SNx 1, 2, and 4 week groups. In SNx 8 week and PAN 4 and 8 week groups, only a few glomeruli with periglomerular calponin-reactivity, which covered half or a very small part of the periglomerular space, were observed. All glomeruli with periglomerular calponin-reactivity showed sclerotic changes, especially thickening of parietal epithelial cells (PECs). In conjunction with our previous report, this data represents the first documentation of the expression of calponin in renal myofibroblasts. We suggest that interactions between PECs and calponin-positive myofibroblasts may play a key role in the late stage of glomerulosclerosis.

Blood pressures, heart rate and locomotor activity during salt loading and angiotensin II infusion in protease-activated receptor 2 (PAR2) knockout mice

Background

In this study we used radiotelemetry to measure hemodynamic variables and locomotor activity in conscious unrestrained male Protease-Activated Receptor 2 (PAR-2) knockout mice in order to provide a detailed assessment of their blood pressure phenotype. In addition we tested for an influence of PAR-2 on salt-sensitivity (8% versus 0.5% NaCl diet, 2.5 weeks) and angiotensin II-induced hypertension (1 μg Ile⁵-angiotensin II/kg/min versus 0.25 μl/h saline, 2 weeks).

Results

Systolic arterial pressures of PAR-2 -/- (129 ± 1 mmHg, n = 21, P < 0.05) were statistically higher than those of C57BL/6J (124 ± 1 mmHg, n = 33) throughout the 24 h period under baseline conditions. Pulse pressures in PAR-2 -/- were also significantly elevated (33 ± 1 mmHg versus 30 ± 1 mmHg, P < 0.05), whereas diastolic arterial pressures were not. Heart rates in PAR-2 -/- were not significantly different than controls, with the exception that heart rate of PAR-2 -/- was 23 beats per min higher than controls (P < 0.001) during periods of nocturnal activity. The diurnal pattern and intensity of locomotor activity were not found to differ between strains. A high salt diet led to increased blood pressures, decreased heart rates, increased time spent active and decreased intensity levels of locomotor activity. Salt-induced changes in systolic and pulse pressures in PAR-2 -/- were less than in C57B/6J. Angiotensin II treatment increased pressures, decreased heart rates, decreased time spent active and decreased intensity levels of activity of PAR-2 -/-, all to the same extent as C57BL/6J. A trend of lower blood pressures during the middle period of angiotensin II treatment period was observed in individual PAR-2 -/-.

Conclusion

The data indicated gene knockout of PAR-2 was associated with a modest change in blood pressure phenotype. PAR-2 -/- mice exhibited moderate elevation of systolic arterial and pulse pressures, yet no increased diastolic arterial pressure, no increased blood pressure responses to high salt diet and a subtle difference in the time course of the blood pressure responses to angiotensin II infusion.

Pathogenesis of essential hypertension: historical paradigms and modern insights

Since its first identification in the late 1800s, a variety of etiologies for essential hypertension have been proposed. In this paper we review the primary proposed hypotheses in the context of both the time in which they were proposed as well as the subsequent studies performed over the years. From these various insights, we propose a current paradigm to explain the renal mechanisms underlying the hypertension epidemic today. Specifically, we propose that hypertension is initiated by agents that cause systemic and intrarenal vasoconstriction. Over time intrarenal injury develops with microvascular disease, interstitial T cell and macrophage recruitment with the induction of an autoimmune response, with local angiotensin II formation and oxidant generation. These changes maintain intrarenal vasoconstriction and hypoxia with a change in local vasoconstrictor-vasodilator balance favoring sodium retention. Both genetic and congenital (nephron number) mechanisms have profound influence on this pathway. As blood pressure rises, renal ischemia is ameliorated and sodium balance restored completely (in salt-resistant) or partially (in salt-sensitive) hypertension, but at the expense of a rightward shift in the pressure natriuresis curve and persistent hypertension.