Cardiovascular characterization of Pkd2+/LacZ mice, an animal model for the autosomal dominant polycystic kidney disease type 2 (ADPKD2)

Echocardiographic Findings and Genotypes in Autosomal Dominant Polycystic Kidney Disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary cystic kidney disease and is well known to have extrarenal complications. Cardiovascular complications are of particular clinical relevance because of their morbidity and mortality; however, unclear is why they occur so frequently in patients with ADPKD and whether they are related to the genotypes.

Methods

We extracted and retrospectively analyzed clinical data on patients with ADPKD who underwent echocardiography and whose genotype was confirmed by genetic testing between April 2016 and December 2020. We used next-generation sequencing to compare cardiac function, structural data, and the presence of cardiac valvular disease in patients with 1 of 3 genotypes: PKD1, PKD2, and non-PKD1, 2.

Results

This retrospective study included 65 patients with ADPKD. Patients were divided into 3 groups: PKD1, n = 32; PKD2, n = 12; and non-PKD1, 2, n = 21. The prevalence of mitral regurgitation (MR) was significantly higher in the PKD1 group than in the PKD2 and non-PKD1, 2 group (46.9% vs. 8.3% vs. 19.0%, respectively; p = 0.02). In contrast, no significant difference was found for other cardiac valve complications.

Conclusion

This study found a significantly higher prevalence of MR in patients with the PKD1 genotype than in those with the PKD2 or non-PKD1, 2 genotypes. Physicians may need to perform echocardiography earlier and more frequently in patients with ADPKD and the PKD1 genotype and to control fluid volume and blood pressure more strictly in these patients to prevent future cardiac events.

Polycystins, ADPKD, and Cardiovascular Disease

Cardiovascular disorders are the most common cause of mortality in autosomal dominant polycystic kidney disease (ADPKD). This review considers recent clinical and basic science studies that address the contributing factors of cardiovascular dysfunction in ADPKD. In particular, attention is placed on how dysfunction of the polycystin proteins located in the cardiovascular system contributes to extrarenal manifestations of ADPKD.

Hematopoietic stem cell transplantation and acute kidney injury in children: A comprehensive review

AKI in the setting of HSCT is commonly investigated among adult patients. In the same way, malignancies requiring treatment with HSCT are not limited to the adult patient population, AKI following HSCT is frequently encountered within pediatric patient populations. However, inadequate information regarding epidemiology and pathophysiology specific to pediatric patients prevents development of appropriate and successful therapeutic strategies for those afflicted. Addressing AKI in the context of sinusoidal obstruction syndrome, chemotherapy, thrombotic microangiopathy and hypertension post chemotherapy, glomerulonephritis, and graft versus host disease provides greater insight into renal impairment associated with these HSCT-related ailments. To obtain a better understanding of AKI among pediatric patients receiving HSCT, we investigated the current literature specifically addressing these areas of concern.

Cardiac dysfunction in Pkd1-deficient mice with phenotype rescue by galectin-3 knockout

Alterations in myocardial wall texture stand out among ADPKD cardiovascular manifestations in hypertensive and normotensive patients. To elucidate their pathogenesis, we analyzed the cardiac phenotype in Pkd1(cond/cond)Nestin(cre) (CYG+) cystic mice exposed to increased blood pressure, at 5 to 6 and 20 to 24 weeks of age, and Pkd1(+/-) (HTG+) noncystic mice at 5-6 and 10-13 weeks. Echocardiographic analyses revealed decreased myocardial deformation and systolic function in CYG+ and HTG+ mice, as well as diastolic dysfunction in older CYG+ mice, compared to their Pkd1(cond/cond) and Pkd1(+/+) controls. Hearts from CYG+ and HTG+ mice presented reduced polycystin-1 expression, increased apoptosis, and mild fibrosis. Since galectin-3 has been associated with heart dysfunction, we studied it as a potential modifier of the ADPKD cardiac phenotype. Double-mutant Pkd1(cond/cond):Nestin(cre);Lgals3(-/-) (CYG-) and Pkd1(+/-);Lgals3(-/-) (HTG-) mice displayed improved cardiac deformability and systolic parameters compared to single-mutants, not differing from the controls. CYG- and HTG- showed decreased apoptosis and fibrosis. Analysis of a severe cystic model (Pkd1(V/V); VVG+) showed that Pkd1(V/V);Lgals3(-/-) (VVG-) mice have longer survival, decreased cardiac apoptosis and improved heart function compared to VVG+. CYG- and VVG- animals showed no difference in renal cystic burden compared to CYG+ and VVG+ mice. Thus, myocardial dysfunction occurs in different Pkd1-deficient models and suppression of galectin-3 expression rescues this phenotype.

Decreased Polycystin 2 Levels Result in Non-Renal Cardiac Dysfunction with Aging

Mutations in the gene for polycystin 2 (Pkd2) lead to polycystic kidney disease, however the main cause of mortality in humans is cardiac related. We previously showed that 5 month old Pkd2+/- mice have altered calcium-contractile activity in cardiomyocytes, but have preserved cardiac function. Here, we examined 1 and 9 month old Pkd2+/- mice to determine if decreased amounts of functional polycystin 2 leads to impaired cardiac function with aging. We observed changes in calcium handling proteins in 1 month old Pkd2+/- mice, and these changes were exacerbated in 9 month old Pkd2+/- mice. Anatomically, the 9 month old Pkd2+/- mice had thinner left ventricular walls, consistent with dilated cardiomyopathy, and the left ventricular ejection fraction was decreased. Intriguingly, in response to acute isoproterenol stimulation to examine β-adrenergic responses, the 9 month old Pkd2+/- mice exhibited a stronger contractile response, which also coincided with preserved localization of the β2 adrenergic receptor. Importantly, the Pkd2+/- mice did not have any renal impairment. We conclude that the cardiac-related impact of decreased polycystin 2 progresses over time towards cardiac dysfunction and altered adrenergic signaling. These results provide further evidence that polycystin 2 provides a critical function in the heart, independent of renal involvement.

Complete heart block with diastolic heart failure and pulmonary edema secondary to enlarging previously diagnosed thrombosed aneurysm of sinus of valsalva in a patient with history of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is associated with vascular aneurysms that can affect any part of the vascular tree, like ascending aorta or coronary arteries. Sinus of Valsalva is known as an anatomical dilation at the root of aorta above the aortic valve and very few cases show aneurysm at that site in patients with ADPKD. Sinus of Valsalva aneurysm (SVA) can present with rupture and acute heart failure and infective endocarditis or could be asymptomatic accidentally discovered during cardiac catheterization. We report a case of a 76-year-old male with a unique constellation of cardiovascular anomalies associated with ADPKD. Patient was previously diagnosed with aneurysms affecting ascending aorta, sinus of Valsalva, and coronary arteries. Several years later, he came with complete heart block which was discovered later to be secondary to enlargement of his previously diagnosed thrombosed SVA. His case was complicated with acute heart failure and pulmonary edema. Conclusion. Patients with ADPKD can present with extrarenal manifestations. In our case, aneurysm at sinus of Valsalva was progressively enlarging and presented with complete heart block.

Decreased polycystin 2 expression alters calcium-contraction coupling and changes β-adrenergic signaling pathways

Cardiac disorders are the main cause of mortality in autosomal-dominant polycystic kidney disease (ADPKD). However, how mutated polycystins predispose patients with ADPKD to cardiac pathologies before development of renal dysfunction is unknown. We investigate the effect of decreased levels of polycystin 2 (PC2), a calcium channel that interacts with the ryanodine receptor, on myocardial function. We hypothesize that heterozygous PC2 mice (Pkd2(+/-)) undergo cardiac remodeling as a result of changes in calcium handling, separate from renal complications. We found that Pkd2(+/-) cardiomyocytes have altered calcium handling, independent of desensitized calcium-contraction coupling. Paradoxically, in Pkd2(+/-) mice, protein kinase A (PKA) phosphorylation of phospholamban (PLB) was decreased, whereas PKA phosphorylation of troponin I was increased, explaining the decoupling between calcium signaling and contractility. In silico modeling supported this relationship. Echocardiography measurements showed that Pkd2(+/-) mice have increased left ventricular ejection fraction after stimulation with isoproterenol (ISO), a β-adrenergic receptor (βAR) agonist. Blockers of βAR-1 and βAR-2 inhibited the ISO response in Pkd2(+/-) mice, suggesting that the dephosphorylated state of PLB is primarily by βAR-2 signaling. Importantly, the Pkd2(+/-) mice were normotensive and had no evidence of renal cysts. Our results showed that decreased PC2 levels shifted the βAR pathway balance and changed expression of calcium handling proteins, which resulted in altered cardiac contractility. We propose that PC2 levels in the heart may directly contribute to cardiac remodeling in patients with ADPKD in the absence of renal dysfunction.

Tbx2 and Tbx3 induce atrioventricular myocardial development and endocardial cushion formation

A key step in heart development is the coordinated development of the atrioventricular canal (AVC), the constriction between the atria and ventricles that electrically and physically separates the chambers, and the development of the atrioventricular valves that ensure unidirectional blood flow. Using knock-out and inducible overexpression mouse models, we provide evidence that the developmentally important T-box factors Tbx2 and Tbx3, in a functionally redundant manner, maintain the AVC myocardium phenotype during the process of chamber differentiation. Expression profiling and ChIP-sequencing analysis of Tbx3 revealed that it directly interacts with and represses chamber myocardial genes, and induces the atrioventricular pacemaker-like phenotype by activating relevant genes. Moreover, mutant mice lacking 3 or 4 functional alleles of Tbx2 and Tbx3 failed to form atrioventricular cushions, precursors of the valves and septa. Tbx2 and Tbx3 trigger development of the cushions through a regulatory feed-forward loop with Bmp2, thus providing a mechanism for the co-localization and coordination of these important processes in heart development.

ADPKD: Prototype of Cardiorenal Syndrome Type 4

The cardiorenal syndrome type 4 (Chronic Renocardiac Syndrome) is characterized by a condition of primary chronic kidney disease (CKD) that leads to an impairment of the cardiac function, ventricular hypertrophy, diastolic dysfunction, and/or increased risk of adverse cardiovascular events. Clinically, it is very difficult to distinguish between CRS type 2 (Chronic Cardiorenal Syndrome) and CRS type 4 (Chronic Renocardiac Syndrome) because often it is not clear whether the primary cause of the syndrome depends on the heart or the kidney. Autosomal dominant polycystic kidney disease (ADPKD), a genetic disease that causes CKD, could be viewed as an ideal prototype of CRS type 4 because it is certain that the primary cause of cardiorenal syndrome is the kidney disease. In this paper, we will briefly review the epidemiology of ADPKD, conventional and novel biomarkers which may be useful in following the disease process, and prevention and treatment strategies.

Feasibility of functional cardiac MR imaging in mice using a clinical 3 Tesla whole body scanner

OBJECTIVES

To test the feasibility of cardiac MR imaging in mice using a clinical 3 Tesla whole body MR system for structural and functional analysis. Standard protocols for bright blood cine imaging were adapted for murine dimensions. To validate measurements of functional parameters the MR data were compared with high-resolution echocardiographic measurements.

MATERIALS AND METHODS

Cardiac imaging was carried out in CD 1 wild-type mice (n = 8). MR imaging studies were performed using a clinical 3 Tesla MR system (Achieva, Philips). All mice received 2 MR scans and 1 echocardiographic evaluation. For optimal MR signal detection a dedicated solenoid receive-only coil was used. Electrocardiogram signal was recorded using a dedicated small animal electrocardiogram monitoring unit. For imaging we used a retrospectively triggered TFE sequence with a repetition time of 12 ms and an echo time of 4 ms. A dedicated software patch allowed for triggering of cardiac frequency of up to 600 BPM. Doppler-echocardiography was performed using a VisualSonics Vevo 770 high-resolution imaging system with a 30 MHz scanhead. Axial/lateral resolution was 40 of 100 microm and temporal resolution was 150 to 300 frames/s (B-mode) and 1000 frames/s (M-mode) depending on the setting.

RESULTS

MR imaging was successfully carried out in all mice with a sufficient temporal resolution and good signal-to-noise ratio and contrast-to-noise ratio levels allowing for identification of all relevant structures. Accordingly, there was a good scan-rescan reproducibility of MR measurements: Interassay coefficients of variance ranged from 4% for ejection fraction to 12% for endsystolic volume (ESV). Magnetic resonance imaging and echocardiography gave comparable results when using the same geometric model (Teichholz method): EDV: 60.2 +/- 6.1 microL/59.1 +/- 12.3 microL, ESV: 20.0 +/- 2.6 microL/20.7 +/- 7.7 microL, EF: 66.7% +/- 4.0%/65.2% +/- 9.9%, CO 19.5 +/- 3.6 mL/17.9 +/- 2.9 mL. Bland-Altman analysis gave acceptable limits of agreement between both methods: EDV (+28.2/-26.1), ESV (+16.3/-17.7), EF (+19.0/-16.1), CO (10.7/-7.5). When applying the Simpson's method MR volume estimates were significantly higher compared with echocardiography resulting in a lower estimate for the ejection fraction (60% +/- 3.9% vs. 66.7% +/- 4.0%).

CONCLUSIONS

Cardiac MR imaging of mice using a clinical 3 Tesla MR system for functional analysis is feasible with sufficient spatial and temporal resolution, good repeatability and reliable results when compared with high-resolution echocardiography.

Echocardiographic assessment of global left ventricular function in mice

Doppler-echocardiographic assessment of cardiovascular structure and function in murine models has developed into one of the most commonly used non-invasive techniques during the last decades. Recent technical improvements even expanded the possibilities. In this review, we summarize the current options to assess global left ventricular (LV) function in mice using echocardiographic techniques. In detail, standard techniques as structural and functional assessment of the cardiovascular phenotype using one-dimensional M-mode echocardiography, two-dimensional B-mode echocardiography and spectral Doppler signals from mitral inflow respective aortal outflow are presented. Further pros and contras of recently implemented techniques as three-dimensional echocardiography and strain and strain rate measurements are discussed. Deduced measures of LV function as the myocardial performance index according to Tei, estimation of the mean velocity of circumferential fibre shortening, LV wall stress and different algorithms to estimate the LV mass are described in detail. Last but not least, specific features and limitations of murine echocardiography are presented. Future perspectives in respect to new examination techniques like targeted molecular imaging with advanced ultrasound contrast bubbles or improvement of equipment like new generation matrix transducers for murine echocardiography are discussed.