Calcium sensing receptor regulates cardiomyocyte function through nuclear calcium

Calcium-Sensing Receptor (CaSR)-Mediated Intracellular Communication in Cardiovascular Diseases

The calcium-sensing receptor (CaSR), a G-protein-coupled receptor (GPCR), is a cell-surface-located receptor that can induce highly diffusible messengers (IP3, Ca²⁺, cAMP) in the cytoplasm to activate various cellular responses. Recently, it has also been suggested that the CaSR mediates the intracellular communications between the endoplasmic reticulum (ER), mitochondria, nucleus, protease/proteasome, and autophagy-lysosome, which are involved in related cardiovascular diseases. The complex intracellular signaling of this receptor challenges it as a valuable therapeutic target. It is, therefore, necessary to understand the mechanisms behind the signaling characteristics of this receptor in intracellular communication. This review provides an overview of the recent research progress on the various regulatory mechanisms of the CaSR in related cardiovascular diseases and the heart-kidney interaction; the associated common causes are also discussed.

Stachydrine hydrochloride suppresses phenylephrine-induced pathological cardiac hypertrophy by inhibiting the calcineurin/nuclear factor of activated T-cell signalling pathway

The calcineurin (CaN)/nuclear factor of activated T-cell (NFAT) signalling pathway plays an important role in pathological cardiac hypertrophy. Here, we investigated the potential effects of stachydrine hydrochloride, a bioactive constituent extracted from the Chinese herb Leonurus japonicus Houtt. (Yimucao), on pathological cardiac hypertrophy during chronic α1-adrenergic receptor (α1-AR) activation and the underlying mechanisms. First, by transcriptome analysis, we determined that pathological hypertrophy models could be prepared after phenylephrine stimulation. In primary cultured neonatal rat ventricular myocytes, stachydrine hydrochloride reduced phenylephrine-induced cardiomyocyte surface area and the mRNA expression of cardiac hypertrophy biomarkers (atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and β-myosin heavy chain/α-myosin heavy chain (β-MHC/α-MHC)). In addition, phenylephrine stimulation potently induced activation of the CaN/NFAT pathway. Interestingly, stachydrine hydrochloride inhibited CaN activation and reduced NFATc3 nuclear translocation in phenylephrine-stimulated neonatal rat ventricular myocytes. In mice treated with phenylephrine, stachydrine hydrochloride treatment decreased cardiac hypertrophy and regulated heart function. Collectively, our data show that stachydrine hydrochloride decreases cardiac hypertrophy in phenylephrine-stimulated hearts by inhibiting the CaN/NFAT pathway, which might contribute to alleviation of pathological cardiac hypertrophy and cardiac dysfunction by stachydrine hydrochloride after phenylephrine stimulation This also indicated that governing of CaN/NFAT pathway might serve as a preventive or therapeutic strategy for pathological cardiac hypertrophy.

Structural and Mechanistic Bases of Nuclear Calcium Signaling in Human Pluripotent Stem Cell-Derived Ventricular Cardiomyocytes

The loss of nonregenerative, terminally differentiated cardiomyocytes (CMs) due to aging or diseases is generally considered irreversible. Human pluripotent stem cells (hPSCs) can self-renew while maintaining their pluripotency to differentiate into all cell types, including ventricular (V) cardiomyocytes (CMs), to provide a potential unlimited ex vivo source of CMs for heart disease modeling, drug/cardiotoxicity screening, and cell-based therapies. In the human heart, cytosolic Ca²⁺ signals are well characterized but the contribution of nuclear Ca²⁺ is essentially unexplored. The present study investigated nuclear Ca²⁺ signaling in hPSC-VCMs. Calcium transient or sparks in hPSC-VCMs were measured by line scanning using a spinning disc confocal microscope. We observed that nuclear Ca²⁺, which stems from unitary sparks due to the diffusion of cytosolic Ca²⁺ that are mediated by RyRs on the nuclear reticulum, is functional. Parvalbumin- (PV-) mediated Ca²⁺ buffering successfully manipulated Ca²⁺ transient and stimuli-induced apoptosis in hPSC-VCMs. We also investigated the effect of Ca²⁺ on gene transcription in hPSC-VCMs, and the involvement of nuclear factor of activated T-cell (NFAT) pathway was identified. The overexpression of Ca²⁺-sensitive, nuclear localized Ca²⁺/calmodulin-dependent protein kinase II δ_B (CaMKIIδ_B) induced cardiac hypertrophy through nuclear Ca²⁺/CaMKIIδB/HDAC4/MEF2 pathway. These findings provide insights into nuclear Ca²⁺ signal in hPSC-VCMs, which may lead to novel strategies for maturation as well as improved systems for disease modeling, drug discovery, and cell-based therapies.

The Different Facets of Extracellular Calcium Sensors: Old and New Concepts in Calcium-Sensing Receptor Signalling and Pharmacology

The current interest of the scientific community for research in the field of calcium sensing in general and on the calcium-sensing Receptor (CaR) in particular is demonstrated by the still increasing number of papers published on this topic. The extracellular calcium-sensing receptor is the best-known G-protein-coupled receptor (GPCR) able to sense external Ca2+ changes. Widely recognized as a fundamental player in systemic Ca2+ homeostasis, the CaR is ubiquitously expressed in the human body where it activates multiple signalling pathways. In this review, old and new notions regarding the mechanisms by which extracellular Ca2+ microdomains are created and the tools available to measure them are analyzed. After a survey of the main signalling pathways triggered by the CaR, a special attention is reserved for the emerging concepts regarding CaR function in the heart, CaR trafficking and pharmacology. Finally, an overview on other Ca2+ sensors is provided.

Herpud1 negatively regulates pathological cardiac hypertrophy by inducing IP3 receptor degradation

Cardiac hypertrophy is an adaptive response triggered by pathological stimuli. Regulation of the synthesis and the degradation of the Ca²⁺ channel inositol 1,4,5-trisphosphate receptor (IP3R) affects progression to cardiac hypertrophy. Herpud1, a component of the endoplasmic reticulum-associated degradation (ERAD) complex, participates in IP3R1 degradation and Ca²⁺ signaling, but the cardiac function of Herpud1 remains unknown. We hypothesize that Herpud1 acts as a negative regulator of cardiac hypertrophy by regulating IP3R protein levels. Our results show that Herpud1-knockout mice exhibit cardiac hypertrophy and dysfunction and that decreased Herpud1 protein levels lead to elevated levels of hypertrophic markers in cultured rat cardiomyocytes. In addition, IP3R levels were elevated both in Herpud1-knockout mice and Herpud1 siRNA-treated rat cardiomyocytes. The latter treatment also led to elevated cytosolic and nuclear Ca²⁺ levels. In summary, the absence of Herpud1 generates a pathological hypertrophic phenotype by regulating IP3R protein levels. Herpud1 is a novel negative regulator of pathological cardiac hypertrophy.

An integrated mechanism of cardiomyocyte nuclear Ca(2+) signaling

In cardiomyocytes, Ca(2+) plays a central role in governing both contraction and signaling events that regulate gene expression. Current evidence indicates that discrimination between these two critical functions is achieved by segregating Ca(2+) within subcellular microdomains: transcription is regulated by Ca(2+) release within nuclear microdomains, and excitation-contraction coupling is regulated by cytosolic Ca(2+). Accordingly, a variety of agonists that control cardiomyocyte gene expression, such as endothelin-1, angiotensin-II or insulin-like growth factor-1, share the feature of triggering nuclear Ca(2+) signals. However, signaling pathways coupling surface receptor activation to nuclear Ca(2+) release, and the phenotypic responses to such signals, differ between agonists. According to earlier hypotheses, the selective control of nuclear Ca(2+) signals by activation of plasma membrane receptors relies on the strategic localization of inositol trisphosphate receptors at the nuclear envelope. There, they mediate Ca(2+) release from perinuclear Ca(2+) stores upon binding of inositol trisphosphate generated in the cytosol, which diffuses into the nucleus. More recently, identification of such receptors at nuclear membranes or perinuclear sarcolemmal invaginations has uncovered novel mechanisms whereby agonists control nuclear Ca(2+) release. In this review, we discuss mechanisms for the selective control of nuclear Ca(2+) signals with special focus on emerging models of agonist receptor activation.

Gender-specific potential inhibitory role of Ca2+/calmodulin dependent protein kinase phosphatase (CaMKP) in pressure-overloaded mouse heart

Background

Ca²⁺/calmodulin-dependent protein kinase phosphatase (CaMKP) has been proposed as a potent regulator of multifunctional Ca²⁺/calmodulin-dependent protein kinases (i.e., CaMKII). The CaMKII-dependent activation of myocyte enhancer factor 2 (MEF2) disrupts interactions between MEF2-histone deacetylases (HDACs), thereby de-repressing downstream gene transcription. Whether CaMKP modulates the CaMKII- MEF2 pathway in the heart is unknown. Here, we investigated the molecular and functional consequences of left ventricular (LV) pressure overload in the mouse of both genders, and in particular we evaluated the expression levels and localization of CaMKP and its association with CaMKII-MEF2 signaling.

Methodology and Principal Findings

Five week-old B6D1/F1 mice of both genders underwent a sham-operation or thoracic aortic constriction (TAC). Thirty days later, TAC was associated with pathological LV hypertrophy characterized by systolic and diastolic dysfunction. Gene expression was assessed by real-time PCR. Fetal gene program re-expression comprised increased RNA levels of brain natriuretic peptide and alpha-skeletal actin. Mouse hearts of both genders expressed both CaMKP transcript and protein. Activation of signalling pathways was studied by Western blot in LV lysates or subcellular fractions (nuclear and cytoplasmic). TAC was associated with increased CaMKP expression in male LVs whereas it tended to be decreased in females. The DNA binding activity of MEF2 was determined by spectrophotometry. CaMKP compartmentalization differed according to gender. In male TAC mice, nuclear CaMKP was associated with inactive CaMKII resulting in less MEF2 activation. In female TAC mice, active CaMKII (phospho-CaMKII) detected in the nuclear fraction, was associated with a strong MEF2 transcription factor-binding activity.

Conclusions/Significance

Gender-specific CaMKP compartmentalization is associated with CaMKII-mediated MEF2 activation in pressure-overloaded hearts. Therefore, CaMKP could be considered as an important novel cellular target for the development of new therapeutic strategies for heart diseases.

Calcium nutrition and extracellular calcium sensing: relevance for the pathogenesis of osteoporosis, cancer and cardiovascular diseases

Through a systematic search in Pubmed for literature, on links between calcium malnutrition and risk of chronic diseases, we found the highest degree of evidence for osteoporosis, colorectal and breast cancer, as well as for hypertension, as the only major cardiovascular risk factor. Low calcium intake apparently has some impact also on cardiovascular events and disease outcome. Calcium malnutrition can causally be related to low activity of the extracellular calcium-sensing receptor (CaSR). This member of the family of 7-TM G-protein coupled receptors allows extracellular Ca2+ to function as a "first messenger" for various intracellular signaling cascades. Evidence demonstrates that Ca2+/CaSR signaling in functional linkage with vitamin D receptor (VDR)-activated pathways (i) promotes osteoblast differentiation and formation of mineralized bone; (ii) targets downstream effectors of the canonical and non-canonical Wnt pathway to inhibit proliferation and induce differentiation of colorectal cancer cells; (iii) evokes Ca2+ influx into breast cancer cells, thereby activating pro-apoptotic intracellular signaling. Furthermore, Ca2+/CaSR signaling opens Ca2+-sensitive K+ conductance channels in vascular endothelial cells, and also participates in IP(3)-dependent regulation of cytoplasmic Ca2+, the key intermediate of cardiomyocyte functions. Consequently, impairment of Ca2+/CaSR signaling may contribute to inadequate bone formation, tumor progression, hypertension, vascular calcification and, probably, cardiovascular disease.