Cardiac Localized Polycystin-2 plays a Functional Role in Natriuretic Peptide Production and its Absence Contributes to Hypertension.

Cardiovascular complications are the most common cause of mortality in patients with autosomal dominant polycystic kidney disease (ADPKD). Hypertension is seen in 70% of patients by the age of 30 prior to decline in kidney function. The natriuretic peptides (NPs), atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), are released by cardiomyocytes in response to membrane stretch, increasing urinary excretion of sodium and water. Mice heterozygous for Pkd2 have attenuated NP responses and we hypothesized that cardiomyocyte-localized polycystin proteins contribute to production of NPs. Cardiomyocyte-specific knock-out models of polycystin-2 (PC2), one of the causative genes of ADPKD, demonstrate diurnal hypertension. These mice have decreased ANP and BNP expression in the left ventricle. Analysis of the pathways involved in production, maturation, and activity of NPs identified decreased transcription of CgB, PCSK6, and NFAT genes in cPC2-KOs. Engineered heart tissue with human iPSCs driven into cardiomyocytes with CRISPR/Cas9 KO of PKD2 failed to produce ANP. These results suggest that PC2 in cardiomyocytes are involved in NP production and lack of cardiac PC2 predisposes to a hypertensive volume expanded phenotype, which may contribute to the development of hypertension in ADPKD.

Cardiomyocyte external mechanical unloading activates modifications of α-actinin differently from sarcomere-originated unloading.

Loss of myocardial mass in a neonatal rat cardiomyocyte culture is studied to determine whether there is a distinguishable cellular response based on the origin of mechano-signals. The approach herein compares the sarcomeric assembly and disassembly processes in heart cells by imposing mechano-signals at the interface with the extracellular matrix (extrinsic) and at the level of the myofilaments (intrinsic). Experiments compared the effects of imposed internal (inside/out) and external (outside/in) loading and unloading on modifications in neonatal rat cardiomyocytes. Unloading of the cellular substrate by myosin inhibition (1 µm mavacamten), or cessation of cyclic strain (1 Hz, 10% strain) after preconditioning, led to significant disassembly of sarcomeric α-actinin by 6 h. In myosin inhibition, this was accompanied by redistribution of intracellular poly-ubiquitin K48 to the cellular periphery relative to the poly-ubiquitin K48 reservoir at the I-band. Moreover, loading and unloading of the cellular substrate led to a three-fold increase in post-translational modifications (PTMs) when compared to the myosin-specific activation or inhibition. Specifically, phosphorylation increased with loading while ubiquitination increased with unloading, which may involve extracellular signal-regulated kinase 1/2 and focal adhesion kinase activation. The identified PTMs, including ubiquitination, acetylation, and phosphorylation, are proposed to modify internal domains in α-actinin to increase its propensity to bind F-actin. These results demonstrate a link between mechanical feedback and sarcomere protein homeostasis via PTMs of α-actinin that exemplify how cardiomyocytes exhibit differential responses to the origin of force. The implications of sarcomere regulation governed by PTMs of α-actinin are discussed with respect to cardiac atrophy and heart failure.

Polycystin-2 (PC2) is a key determinant of in vitro myogenesis.

The development of skeletal muscle (myogenesis) is a well-orchestrated process where myoblasts withdraw from the cell cycle and differentiate into myotubes. Signaling by fluxes in intracellular calcium (Ca2+) is known to contribute to myogenesis, and increased mitochondrial biogenesis is required to meet the metabolic demand of mature myotubes. However, gaps remain in the understanding of how intracellular Ca2+ signals can govern myogenesis. Polycystin-2 (PC2 or TRPP1) is a nonselective cation channel permeable to Ca2+. It can interact with intracellular calcium channels to control Ca2+ release and concurrently modulates mitochondrial function and remodeling. Due to these features, we hypothesized that PC2 is a central protein in mediating both the intracellular Ca2+ responses and mitochondrial changes seen in myogenesis. To test this hypothesis, we created CRISPR/Cas9 knockout (KO) C2C12 murine myoblast cell lines. PC2 KO cells were unable to differentiate into myotubes, had impaired spontaneous Ca2+ oscillations, and did not develop depolarization-evoked Ca2+ transients. The autophagic-associated pathway beclin-1 was downregulated in PC2 KO cells, and direct activation of the autophagic pathway resulted in decreased mitochondrial remodeling. Re-expression of full-length PC2, but not a calcium channel dead pathologic mutant, restored the differentiation phenotype and increased the expression of mitochondrial proteins. Our results establish that PC2 is a novel regulator of in vitro myogenesis by integrating PC2-dependent Ca2+ signals and metabolic pathways.

Deletion of cardiac polycystin 2/PC2 results in increased SR calcium release and blunted adrenergic reserve.

Transient receptor potential proteins (TRPs) act as nonselective cation channels. Of the TRP channels, PC2 (also known as polycystin 2) is localized to the sarcoplasmic reticulum (SR); however, its contribution to calcium-induced calcium release and overall cardiac function in the heart is poorly understood. The goal of this study was to characterize the effect of cardiac-specific PC2 deletion in adult cardiomyocytes and in response to chronic ß-adrenergic challenge. We used a temporally inducible model to specifically delete PC2 from cardiomyocytes (Pkd2 KO) and characterized calcium and contractile dynamics in single cells. We found enhanced intracellular calcium release after Pkd2 KO, and near super-resolution microscopy analysis suggested this was due to close localization of PC2 to the ryanodine receptor. At the organ level, speckle-tracking echocardiographical analysis showed increased dyssynchrony in the Pkd2 KO mice. In response to chronic adrenergic stimulus, cardiomyocytes from the Pkd2 KO had no reserve ß-adrenergic calcium responses and significantly attenuated wall motion in the whole heart. Biochemically, without adrenergic stimulus, there was an overall increase in PKA phosphorylated targets in the Pkd2 KO mouse, which decreased following chronic adrenergic stimulus. Taken together, our results suggest that cardiac-specific PC2 limits SR calcium release by affecting the PKA phosphorylation status of the ryanodine receptor, and the effects of PC2 loss are exacerbated upon adrenergic challenge.NEW & NOTEWORTHY Our goal was to characterize the role of the transient receptor potential channel polycystin 2 (PC2) in cardiomyocytes following adult-onset deletion. Loss of PC2 resulted in decreased cardiac shortening and cardiac dyssynchrony and diminished adrenergic reserve. These results suggest that cardiac-specific PC2 modulates intracellular calcium signaling and contributes to the maintenance of adrenergic pathways.

Mapping behaviorally relevant light pollution levels to improve urban habitat planning.

Artificial nighttime lights have important behavioral and ecological effects on wildlife. Combining laboratory and field techniques, we identified behaviorally relevant levels of nighttime light and mapped the extent of these light levels across the city of Chicago. We began by applying a Gaussian finite mixture model to 998 sampled illumination levels around Chicago to identify clusters of light levels. A simplified sample of these levels was replicated in the laboratory to identify light levels at which C57BL/6J mice exhibited altered circadian activity patterns. We then used camera trap and high-altitude photographic data to compare our field and laboratory observations, finding activity pattern changes in the field consistent with laboratory observations. Using these results, we mapped areas across Chicago exposed to estimated illumination levels above the value associated with statistically significant behavioral changes. Based on this measure, we found that as much as 36% of the greenspace in the city is in areas illuminated at levels greater than or equal to those at which we observe behavioral differences in the field and in the laboratory. Our findings provide evidence that artificial lighting patterns may influence wildlife behavior at a broad scale throughout urban areas, and should be considered in urban habitat planning.