cGMP-dependent protein kinases (cGK)

The Research Progress of DNA Methylation in the Development and Function of the Porcine Placenta

The pig is the most widely consumed domestic animal in China, providing over half of the meat supply in food markets. For livestock, a key economic trait is the reproductive performance, which is significantly influenced by placental development. The placenta, a temporary fetal organ, is crucial for establishing maternal-fetal communication and supporting fetal growth throughout pregnancy. DNA methylation is an epigenetic modification that can regulate the gene expression by recruiting proteins involved in gene silencing or preventing transcription factor binding. To enhance our understanding of the molecular mechanisms underlying DNA methylation in porcine placental development, this review summarizes the structure and function of the porcine placenta and the role of DNA methylation in placental development.

Abnormal phosphorylation / dephosphorylation and Ca2+ dysfunction in heart failure

Heart failure (HF) can be caused by a variety of causes characterized by abnormal myocardial systole and diastole. Ca2+ current through the L-type calcium channel (LTCC) on the membrane is the initial trigger signal for a cardiac cycle. Declined systole and diastole in HF are associated with dysfunction of myocardial Ca2+ function. This disorder can be correlated with unbalanced levels of phosphorylation / dephosphorylation of LTCC, endoplasmic reticulum (ER), and myofilament. Kinase and phosphatase activity changes along with HF progress, resulting in phased changes in the degree of phosphorylation / dephosphorylation. It is important to realize the phosphorylation / dephosphorylation differences between a normal and a failing heart. This review focuses on phosphorylation / dephosphorylation changes in the progression of HF and summarizes the effects of phosphorylation / dephosphorylation of LTCC, ER function, and myofilament function in normal conditions and HF based on previous experiments and clinical research. Also, we summarize current therapeutic methods based on abnormal phosphorylation / dephosphorylation and clarify potential therapeutic directions.

Single-Nucleus RNA-Seq Reveals Spermatogonial Stem Cell Developmental Pattern in Shaziling Pigs

Normal testicular development ensures the process of spermatogenesis, which is a complex biological process. The sustained high productivity of spermatogenesis throughout life is predominantly attributable to the constant proliferation and differentiation of spermatogonial stem cells (SSCs). The self-renewal and differentiation processes of SSCs are strictly regulated by the SSC niche. Therefore, understanding the developmental pattern of SSCs is crucial for spermatogenesis. The Shaziling pig is a medium-sized indigenous pig breed originating from central China. It is renowned for its superior meat quality and early male sexual maturity. The spermatogenic ability of the boars is of great economic importance to the pig industry. To investigate testicular development, particularly the pattern of SSC development in Shaziling pigs, we used single-cell transcriptomics to identify gene expression patterns in 82,027 individual cells from nine Shaziling pig testes at three key postnatal developmental stages. We generated an unbiased cell developmental atlas of Shaziling pig testicular tissues. We elucidated the complex processes involved in the development of SSCs within their niche in the Shaziling pig. Specifically, we identified potential marker genes and cellular signaling pathways that regulate SSC self-renewal and maintenance. Additionally, we proposed potential novel marker genes for SSCs that could be used for SSC isolation and sorting in Shaziling pigs. Furthermore, by immunofluorescence staining of testicular tissues of different developmental ages using marker proteins (UCHL1 and KIT), the developmental pattern of the spermatogonia of Shaziling pigs was intensively studied. Our research enhances the comprehension of the development of SSCs and provides a valuable reference for breeding Shaziling pigs.

Insights on Platelet-Derived Growth Factor Receptor α-Positive Interstitial Cells in the Male Reproductive Tract

Male infertility is a significant factor in approximately half of all infertility cases and is marked by a decreased sperm count and motility. A decreased sperm count is caused by not only a decreased production of sperm but also decreased numbers successfully passing through the male reproductive tract. Smooth muscle movement may play an important role in sperm transport in the male reproductive tract; thus, understanding the mechanism of this movement is necessary to elucidate the cause of sperm transport disorder. Recent studies have highlighted the presence of platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells (PICs) in various smooth muscle organs. Although research is ongoing, PICs in the male reproductive tract may be involved in the regulation of smooth muscle movement, as they are in other smooth muscle organs. This review summarizes the findings to date on PICs in male reproductive organs. Further exploration of the structural, functional, and molecular characteristics of PICs could provide valuable insights into the pathogenesis of male infertility and potentially lead to new therapeutic approaches.

The role of miRNA molecules in the miscarriage process

The etiology and pathogenesis of miscarriage, which is the most common pregnancy complication, have not been fully elucidated. There is a constant search for new screening biomarkers that would allow for the early diagnosis of disorders associated with pregnancy pathology. The profiling of microRNA expression is a promising research area, which can help establish the predictive factors for pregnancy diseases. Molecules of microRNAs are involved in several processes crucial for the development and functioning of the body. These processes include cell division and differentiation, programmed cell death, blood vessel formation or tumorigenesis, and the response to oxidative stress. The microRNAs affect the number of individual proteins in the body due to their ability to regulate gene expression at the post-transcriptional level, ensuring the normal course of many cellular processes. Based on the scientific facts available, this paper presents a compendium on the role of microRNA molecules in the miscarriage process. The expression of potential microRNA molecules as early minimally invasive diagnostic biomarkers may be evaluated as early as the first weeks of pregnancy and may constitute a monitoring factor in the individual clinical care of women in early pregnancy, especially after the first miscarriage. To summarize, the described scientific data set a new direction of research in the development of preventive care and prognostic monitoring of the course of pregnancy.

Bibliometric study of soluble guanylate cyclase stimulators in cardiovascular research based on web of science from 1992 to 2021

Background: Several studies have shown that soluble guanylate cyclase (sGC) stimulators have cardiovascular (CV) benefits. However, few bibliometric analyses have examined this field systematically. Our study aimed to examine the publications to determine the trends and hotspots in CV research on sGC stimulators.

Methods: Publications on sGC stimulators in CV research were retrieved from the Web of Science Core Collection. VOSviewer and CiteSpace visualization software were used to analyze publication trends, countries (regions) and institutions, journals and cited journals, authors and cited references, as well as keywords.

Results: A total of 1,212 literatures were obtained. From its first appearance in 1992–2021 (based on WOSCC record), the overall volume of publications has shown a gradual increasing trend. Nearly one-third were authored by American scholars, and most were published in Circulation, Circulation Research, and Proceedings of the National Academy of Sciences of the United States of America. Bayer Agency in Germany was the leading driving force, and has a high academic reputation in this field. Stasch JP has published the most related articles and been cited most frequently. Half of the top 10 co-cited references were published in the leading highly co-cited journal Circulation and New England Journal of Medicine. “NO,” “allosteric regulation” and “free radicals” were the focus of previous research, “chronic thromboembolic pulmonary hypertension,” “pulmonary hypertension” and “heart failure” were the main research hotspots. The key words “chronic thromboembolic pulmonary hypertension,” “Pulmonary hypertension,” “preserved ejection fraction” and “heart failure” appeared most recently as research frontiers.

Conclusion: The research in the CV field of sGC stimulators was relatively comprehensive, and there was a close relationship among countries, research institutions and authors, but it is still in the exploratory stage in the treatment of CV disease. At present, most studies focus on the results of clinical trials. sGC stimulators in the treatment of heart failure, especially heart failure with preserved ejection fraction, may be the hotpots and Frontier at present and in the future, and should be closely monitored.

Ca2+/calmodulin-dependent protein kinase II and protein kinase G oxidation contributes to impaired sarcomeric proteins in hypertrophy model

Aims

Volume overload (VO) induced hypertrophy is one of the hallmarks to the development of heart diseases. Understanding the compensatory mechanisms involved in this process might help preventing the disease progression.

Methods and results

Therefore, the present study used 2 months old Wistar rats, which underwent an aortocaval fistula to develop VO‐induced hypertrophy. The animals were subdivided into four different groups, two sham operated animals served as age‐matched controls and two groups with aortocaval fistula. Echocardiography was performed prior termination after 4‐ and 8‐month. Functional and molecular changes of several sarcomeric proteins and their signalling pathways involved in the regulation and modulation of cardiomyocyte function were investigated.

Results

The model was characterized with preserved ejection fraction in all groups and with elevated heart/body weight ratio, left/right ventricular and atrial weight at 4‐ and 8‐month, which indicates VO‐induced hypertrophy. In addition, 8‐months groups showed increased left ventricular internal diameter during diastole, RV internal diameter, stroke volume and velocity‐time index compared with their age‐matched controls. These changes were accompanied by increased Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness in 8‐month VO rats compared with other groups. The altered cardiomyocyte mechanics was associated with phosphorylation deficit of sarcomeric proteins cardiac troponin I, myosin binding protein C and titin, also accompanied with impaired signalling pathways involved in phosphorylation of these sarcomeric proteins in 8‐month VO rats compared with age‐matched control group. Impaired protein phosphorylation status and dysregulated signalling pathways were associated with significant alterations in the oxidative status of both kinases CaMKII and PKG explaining by this the elevated Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness and perhaps the development of hypertrophy.

Conclusions

Our findings showed VO‐induced cardiomyocyte dysfunction via deranged phosphorylation of myofilament proteins and signalling pathways due to increased oxidative state of CaMKII and PKG and this might contribute to the development of hypertrophy.

Prkg2 regulates alveolar type 2-mediated re-alveolarization

BACKGROUND

The cGMP-dependent type 2 protein kinase, encoded by the prkg2 gene, is highly expressed in alveolar type 2 epithelial (AT2) cells. It is unclear whether prkg2 regulates AT2 cell homeostasis and re-alveolarization of injured lungs. This study aimed to investigate the role of prkg2 in the regulation of the fate of AT2 in vitro.

METHODS

Primary AT2 cells of wild-type (wt) and prkg2^-/- mice were co-cultured with fibroblasts as three-dimensional organoids. The colony formation was analyzed between days 4 and 12 post-seeding. EdU assay was used to detect cells with active DNA synthesis. AT1 and AT2 cells in organoids were visualized with anti-podoplanin and anti-surfactant protein C antibodies, respectively.

RESULTS

Prkg2^-/- AT2 cells developed a greater number of organoids than wt controls. However, compared to wt organoids, a lower number of AT2 but a greater number of AT1 cells were visualized. In addition, a lower number of proliferated cells (EdU⁺) were observed in prkg2^-/- organoids compared to wt controls. The numbers of organoids and EdU⁺ cells were significantly reduced in protein kinase A (PKA) inhibitor H89-treated wt and prkg2^-/- cultures. Organoids and EdU⁺ cells were increased by lipopolysaccharides (LPS) in both wt and prkg2^-/- groups. The increase in the proportion of AT1 and AT2 cells in organoids was only seen in wt controls.

CONCLUSIONS

Prkg2 may regulate the lineage of AT2 cells, which is affected by endotoxins and the interactive PKA signaling pathway.

Extracellular protein kinase A and G are potential biomarkers of some inflammation-associated disorders

Introduction

Protein kinase A (PKA) and protein kinase G (PKG) are the main downstream effectors of second messengers cAMP and cGMP, which play important roles in physiological and pathological processes. Recently, there are two findings: one is PKA catalytic subunits α (PKACα) and PKG II can be secreted, the other is that the two secretory protein kinases are associated with the progression of tumors. Previous data also demonstrate that the two kinases, as signal cascades, involved in inflammation-associated disorders. However, it remains unclear whether the secreted PKACα or PKG II could serve as diagnostic biomarkers for inflammation-associated disorders.

Methods

The serum from suffered coronary disease, diabetes, rheumatoid arthritis, and schizophrenia were collected. The serum PKACα and PKG II were detected by ELISA. All the patients were consent informed.

Results

Our results showed that the serum PKACα and PKG II had obvious changes in coronary disease, rheumatoid arthritis, schizophrenia patients. However, the trends was opposite, especially in rheumatoid arthritis.

Conclusions

Serum PKACα and PKG II could serve as potentially diagnostic biomarkers for some inflammation-associated disorders, such as coronary disease, rheumatoid arthritis, and schizophrenia.

Evolution of the membrane/particulate guanylyl cyclase: From physicochemical sensors to hormone receptors

Guanylyl cyclase (GC) is an enzyme that produces 3',5'-cyclic guanosine monophosphate (cGMP), one of the two canonical cyclic nucleotides used as a second messenger for intracellular signal transduction. The GCs are classified into two groups, particulate/membrane GCs (pGC) and soluble/cytosolic GCs (sGC). In relation to the endocrine system, pGCs include hormone receptors for natriuretic peptides (GC-A and GC-B) and guanylin peptides (GC-C), while sGC is a receptor for nitric oxide and carbon monoxide. Comparing the functions of pGCs in eukaryotes, it is apparent that pGCs perceive various environmental factors such as light, temperature, and various external chemical signals in addition to endocrine hormones, and transmit the information into the cell using the intracellular signaling cascade initiated by cGMP, e.g., cGMP-dependent protein kinases, cGMP-sensitive cyclic nucleotide-gated ion channels and cGMP-regulated phosphodiesterases. Among vertebrate pGCs, GC-E and GC-F are localized on retinal epithelia and are involved in modifying signal transduction from the photoreceptor, rhodopsin. GC-D and GC-G are localized in olfactory epithelia and serve as sensors at the extracellular domain for external chemical signals such as odorants and pheromones. GC-G also responds to guanylin peptides in the urine, which alters sensitivity to other chemicals. In addition, guanylin peptides that are secreted into the intestinal lumen, a pseudo-external environment, act on the GC-C on the apical membrane for regulation of epithelial transport. In this context, GC-C and GC-G appear to be in transition from exocrine pheromone receptor to endocrine hormone receptor. The pGCs also exist in various deuterostome and protostome invertebrates, and act as receptors for environmental, exocrine and endocrine factors including hormones. Tracing the evolutionary history of pGCs, it appears that pGCs first appeared as a sensor for physicochemical signals in the environment, and then evolved to function as hormone receptors. In this review, the author proposes an evolutionary history of pGCs that highlights the emerging role of the GC/cGMP system for signal transduction in hormone action.

Cyclic GMP-Dependent Regulation of Vascular Tone and Blood Pressure Involves Cysteine-Rich LIM-Only Protein 4 (CRP4)

The cysteine-rich LIM-only protein 4 (CRP4), a LIM-domain and zinc finger containing adapter protein, has been implicated as a downstream effector of the second messenger 3',5'-cyclic guanosine monophosphate (cGMP) pathway in multiple cell types, including vascular smooth muscle cells (VSMCs). VSMCs and nitric oxide (NO)-induced cGMP signaling through cGMP-dependent protein kinase type I (cGKI) play fundamental roles in the physiological regulation of vascular tone and arterial blood pressure (BP). However, it remains unclear whether the vasorelaxant actions attributed to the NO/cGMP axis require CRP4. This study uses mice with a targeted deletion of the CRP4 gene (CRP4 KO) to elucidate whether cGMP-elevating agents, which are well known for their vasorelaxant properties, affect vessel tone, and thus, BP through CRP4. Cinaciguat, a NO- and heme-independent activator of the NO-sensitive (soluble) guanylyl cyclase (NO-GC) and NO-releasing agents, relaxed both CRP4-proficient and -deficient aortic ring segments pre-contracted with prostaglandin F2α. However, the magnitude of relaxation was slightly, but significantly, increased in vessels lacking CRP4. Accordingly, CRP4 KO mice presented with hypotonia at baseline, as well as a greater drop in systolic BP in response to the acute administration of cinaciguat, sodium nitroprusside, and carbachol. Mechanistically, loss of CRP4 in VSMCs reduced the Ca2+-sensitivity of the contractile apparatus, possibly involving regulatory proteins, such as myosin phosphatase targeting subunit 1 (MYPT1) and the regulatory light chain of myosin (RLC). In conclusion, the present findings confirm that the adapter protein CRP4 interacts with the NO-GC/cGMP/cGKI pathway in the vasculature. CRP4 seems to be part of a negative feedback loop that eventually fine-tunes the NO-GC/cGMP axis in VSMCs to increase myofilament Ca2+ desensitization and thereby the maximal vasorelaxant effects attained by (selected) cGMP-elevating agents.

A Bioinformatics Investigation into the Pharmacological Mechanisms of Sodium-Glucose Co-transporter 2 Inhibitors in Diabetes Mellitus and Heart Failure Based on Network Pharmacology

PURPOSE

Diabetes mellitus (DM) is a major risk factor for the development of heart failure (HF). Sodium-glucose co-transporter 2 (SGLT2) inhibitors have demonstrated consistent benefits in the reduction of hospitalization for HF in patients with DM. However, the pharmacological mechanism is not clear. To investigate the mechanisms of SGLT2 inhibitors in DM with HF, we performed target prediction and network analysis by a network pharmacology method.

METHODS

We selected targets of SGLT2 inhibitors and DM status with HF from databases and studies. The "Drug-Target" and "Drug-Target-Disease" networks were constructed using Cytoscape. Then the protein-protein interaction (PPI) was analyzed using the STRING database. Gene Ontology (GO) biological functions and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were performed to investigate using the Bioconductor tool for analysis.

RESULTS

There were 125 effective targets between SGLT2 inhibitors and DM status with HF. Through further screening, 33 core targets were obtained, including SRC, MAPK1, NARS, MAPK3 and EGFR. It was predicted that the Rap1 signaling pathway, MAPK signaling pathway, EGFR tyrosine kinase inhibitor resistance, AGE-RAGE signaling pathway in diabetic complications and other signaling pathways were involved in the treatment of DM with HF by SGLT2 inhibitors.

CONCLUSION

Our study elucidated the possible mechanisms of SGLT2 inhibitors from a systemic and holistic perspective based on pharmacological networks. The key targets and pathways will provide new insights for further research on the pharmacological mechanism of SGLT2 inhibitors in the treatment of DM with HF.

C-type natriuretic peptide-induced relaxation through cGMP-dependent protein kinase and SERCA activation is impaired in two kidney-one clip rat aorta

AIMS

Hypertension underlies endothelial dysfunction, and activation of vasorelaxation signaling with low dependence on nitric oxide (NO) represents a good alternative for vascular modulation. C-type natriuretic peptide (CNP) causes relaxation by increasing cyclic guanosine 3',5'-monophosphate (cGMP) or Gi-protein activation through its natriuretic peptide receptor-B or -C, respectively. We have hypothesized that CNP could exerts its effects and could overcome endothelial dysfunction in two kidney-one clip (2K-1C) hypertensive rat aorta. Here, we investigate the intracellular signaling involved in CNP effects in hypertension.

MATERIALS AND METHODS

The 2K-1C hypertension was induced in male Wistar rats (200 g). CNP-induced vascular relaxation and cGMP production were investigated in rat thoracic aortas. The natriuretic peptide receptor-B and -C localization was evaluated by immunofluorescence. Calcium mobilization was assessed in endothelial cells from rat aortas.

KEY FINDINGS

CNP induced similar relaxation in normotensive and 2K-1C hypertensive rat aortas, which increased after endothelium removal. CNP-induced relaxation involved natriuretic peptide receptor-B and -C activation in 2K-1C rats. Nitric oxide synthase (NOS) and soluble guanylyl cyclase (sGC) counter-regulated CNP-particulate GC (pGC) activation in aortas. CNP reduced endothelial calcium and increased cGMP production, which was lower in 2K-1C. CNP-induced cGMP-dependent protein kinase (PKG) and sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activation was impaired in 2K-1C rat aorta.

SIGNIFICANCE

Our results indicated CNP triggered relaxation through its natriuretic peptide receptor-B and -C in 2K-1C rat aortas, and that CNP-induced relaxation overcomes endothelial dysfunction in hypertension. In addition, NOS and sGC activities counter-regulate CNP-pGC activation to induce vascular relaxation.

Cardiac cGMP Signaling in Health and Disease: Location, Location, Location

3',5'-Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger, which critically regulates cardiac pump function and protects from the development of cardiac hypertrophy by acting in various subcellular microdomains. Although clinical studies testing the potential of cGMP elevating drugs in patients suffering from cardiac disease showed promising results, deeper insight into the local actions of these drugs at the subcellular level are indispensable to inspire novel therapeutic strategies. Detailed information on the spatio-temporal dynamics of cGMP production and degradation can be provided by the use of fluorescent biosensors that are capable of monitoring this second messenger at different locations inside the cell with high temporal and spatial resolution. In this review, we will summarize how these emerging new tools have improved our understanding of cardiac cGMP signaling in health and disease, and attempt to anticipate future challenges in the field.

Depletion of cyclic-GMP levels and inhibition of cGMP-dependent protein kinase activate p21Cip1 /p27Kip1 pathways and lead to renal fibrosis and dysfunction

Cell-cycle regulatory proteins (p21^Cip1 /p27^Kip1 ) inhibit cyclin and cyclin-dependent kinase (CDK) complex that promotes fibrosis and hypertrophy. The present study examined the role of CDK blockers, p21^Cip1 /p27^Kip1 in the progression of renal fibrosis and dysfunction using Npr1 (encoding guanylyl cyclase/natriuretic peptide receptor-A, GC-A/NPRA) gene-knockout (0-copy; Npr1^-/- ), 2-copy (Npr1^+/+ ), and 4-copy (Npr1^++/++ ) mice treated with GC inhibitor, A71915 and cGMP-dependent protein kinase (cGK) inhibitor, (Rp-8-Br-cGMPS). A significant decrease in renal cGMP levels and cGK activity was observed in 0-copy mice and A71915- and Rp-treated 2-copy and 4-copy mice compared with controls. An increased phosphorylation of Erk1/2, p38, p21^Cip1 , and p27^Kip1 occurred in 0-copy and A71915-treated 2-copy and 4-copy mice, while Rp treatment caused minimal changes than controls. Pro-inflammatory (TNF-α, IL-6) and pro-fibrotic (TGF-β1) cytokines were significantly increased in plasma and kidneys of 0-copy and A71915-treated 2-copy mice, but to lesser extent in 4-copy mice. Progressive renal pathologies, including fibrosis, mesangial matrix expansion, and tubular hypertrophy were observed in 0-copy and A71915-treated 2-copy and 4-copy mice, but minimally occurred in Rp-treated mice compared with controls. These results indicate that Npr1 has pivotal roles in inhibiting renal fibrosis and hypertrophy and exerts protective effects involving cGMP/cGK axis by repressing CDK blockers p21^Cip1 and p27^Kip1 .

S-palmitoylation Is Required for the Control of Growth Cone Morphology of DRG Neurons by CNP-Induced cGMP Signaling

Genetic investigations have demonstrated that a specific form of axonal branching - the bifurcation of afferents from dorsal root ganglia (DRG), cranial sensory ganglia (CSG) and mesencephalic trigeminal neurons (MTN) – is regulated by a cGMP-dependent signaling pathway. This cascade is composed of the ligand C-type natriuretic peptide (CNP), the receptor guanylyl cyclase Npr2, and the cGMP-dependent protein kinase Iα (cGKIα). In the absence of any one of these components, axons no longer bifurcate, instead they turn in either an ascending or a descending direction. To gain further mechanistic insights into the process of axon bifurcation we applied different cell culture approaches to decipher downstream activities of cGKI in somatosensory growth cones. We demonstrate that CNP induces an enlargement of DRG growth cones via cGKI which is considered as the priming step of axon bifurcation in the spinal cord. This growth cone remodeling was both blocked by pharmacological inhibitors of S-palmitoylation and potentiated by blocking de-palmitoylation. cGKI colocalizes with the palmitoylome and vesicular structures including the endoplasmic reticulum, early endosomes, lysosomes primarily in the central domain of the growth cone as well as with the Golgi apparatus at the level of the soma. Interestingly, an acyl-biotin-exchange chemistry-based screen indicated that 8pCPT-cGMP-induced signaling induces S-palmitoylation of a restricted pool of proteins in the DRG-derived cell line F11. Overall, our data indicate that CNP-induced cGMP signaling via cGKI affects growth cone morphology of somatosensory afferents. Moreover, it also suggests that S-palmitoylation might play a role in this process.

Establishing a Split Luciferase Assay for Proteinkinase G (PKG) Interaction Studies

Nitric oxide (NO/cyclic guanosine monophosphate (cGMP)-regulated cellular mechanisms are involved in a variety of (patho-) physiological processes. One of the main effector molecules in this system, proteinkinase G (PKG), serves as a molecular switch by phosphorylating different target proteins and thereby turning them on or off. To date, only a few interaction partners of PKG have been described although the identification of protein–protein interactions (PPI) is indispensable for the understanding of cellular processes and diseases. Conventionally used methods to detect PPIs exhibit several disadvantages, e.g., co-immunoprecipitations, which depend on suitable high-affinity antibodies. Therefore, we established a cell-based protein-fragment complementation assay (PCA) for the identification of PKG target proteins. Here, a reporter protein (click beetle luciferase) is split into two fragments and fused to two different possible interaction partners. If interaction occurs, the reporter protein is functionally complemented and the catalyzed reaction can then be quantitatively measured. By using this technique, we confirmed the regulator of G-Protein signaling 2 (RGS2) as an interaction partner of PKGIα (a PKG-isoform) following stimulation with 8-Br-cGMP and 8-pCPT-cGMP. Hence, our results support the conclusion that the established approach could serve as a novel tool for the rapid, easy and cost-efficient detection of novel PKG target proteins.

The Absence of Sensory Axon Bifurcation Affects Nociception and Termination Fields of Afferents in the Spinal Cord

A cGMP signaling cascade composed of C-type natriuretic peptide, the guanylyl cyclase receptor Npr2 and cGMP-dependent protein kinase I (cGKI) controls the bifurcation of sensory axons upon entering the spinal cord during embryonic development. However, the impact of axon bifurcation on sensory processing in adulthood remains poorly understood. To investigate the functional consequences of impaired axon bifurcation during adult stages we generated conditional mouse mutants of Npr2 and cGKI (Npr2^fl/fl;Wnt1^Cre and cGKI^KO/fl;Wnt1^Cre) that lack sensory axon bifurcation in the absence of additional phenotypes observed in the global knockout mice. Cholera toxin labeling in digits of the hind paw demonstrated an altered shape of sensory neuron termination fields in the spinal cord of conditional Npr2 mouse mutants. Behavioral testing of both sexes indicated that noxious heat sensation and nociception induced by chemical irritants are impaired in the mutants, whereas responses to cold sensation, mechanical stimulation, and motor coordination are not affected. Recordings from C-fiber nociceptors in the hind limb skin showed that Npr2 function was not required to maintain normal heat sensitivity of peripheral nociceptors. Thus, the altered behavioral responses to noxious heat found in Npr2^fl/fl;Wnt1^Cre mice is not due to an impaired C-fiber function. Overall, these data point to a critical role of axonal bifurcation for the processing of pain induced by heat or chemical stimuli.

A genome-wide gene-by-trauma interaction study of alcohol misuse in two independent cohorts identifies PRKG1 as a risk locus

Traumatic life experiences are associated with alcohol use problems, an association that is likely to be moderated by genetic predisposition. To understand these interactions, we conducted a gene-by-environment genome-wide interaction study (GEWIS) of alcohol use problems in two independent samples, the Army STARRS (STARRS, N=16 361) and the Yale-Penn (N=8084) cohorts. Because the two cohorts were assessed using different instruments, we derived separate dimensional alcohol misuse scales and applied a proxy-phenotype study design. In African-American subjects, we identified an interaction of PRKG1 rs1729578 with trauma exposure in the STARRS cohort and replicated its interaction with trauma exposure in the Yale-Penn cohort (discovery-replication meta-analysis: z=5.64, P=1.69 × 10^-8). PRKG1 encodes cyclic GMP-dependent protein kinase 1, which is involved in learning, memory and circadian rhythm regulation. Considering the loci identified in stage-1 that showed same effect directions in stage-2, the gene ontology (GO) enrichment analysis showed several significant results, including calcium-activated potassium channels (GO:0016286; P=2.30 × 10^-5), cognition (GO:0050890; P=1.90 × 10^-6), locomotion (GO:0040011; P=6.70 × 10^-5) and Stat3 protein regulation (GO:0042517; P=6.4 × 10^-5). To our knowledge, this is the largest GEWIS performed in psychiatric genetics, and the first GEWIS examining risk for alcohol misuse. Our results add to a growing body of literature highlighting the dynamic impact of experience on individual genetic risk.

Structural Basis of Analog Specificity in PKG I and II

Cyclic GMP analogs, 8-Br, 8-pCPT, and PET-cGMP, have been widely used for characterizing cellular functions of cGMP-dependent protein kinase (PKG) I and II isotypes. However, interpreting results obtained using these analogs has been difficult due to their low isotype specificity. Additionally, each isotype has two binding sites with different cGMP affinities and analog selectivities, making understanding the molecular basis for isotype specificity of these compounds even more challenging. To determine isotype specificity of cGMP analogs and their structural basis, we generated the full-length regulatory domains of PKG I and II isotypes with each binding site disabled, determined their affinities for these analogs, and obtained cocrystal structures of both isotypes bound with cGMP analogs. Our affinity and activation measurements show that PET-cGMP is most selective for PKG I, whereas 8-pCPT-cGMP is most selective for PKG II. Our structures of cyclic nucleotide binding (CNB) domains reveal that the B site of PKG I is more open and forms a unique π/π interaction through Arg285 at β4 with the PET moiety, whereas the A site of PKG II has a larger β5/β6 pocket that can better accommodate the bulky 8-pCPT moiety. Our structural and functional results explain the selectivity of these analogs for each PKG isotype and provide a starting point for the rational design of isotype selective activators.

Conventional and Unconventional Mechanisms for Soluble Guanylyl Cyclase Signaling

Soluble guanylyl cyclase (sGC) is the principal enzyme in mediating the biological actions of nitric oxide. On activation, sGC converts guanosine triphosphate to guanosine 3',5'-cyclic monophosphate (cGMP), which mediates diverse physiological processes including vasodilation, platelet aggregation, and myocardial functions predominantly by acting on cGMP-dependent protein kinases. Cyclic GMP has long been considered as the sole second messenger for sGC action. However, emerging evidence suggests that, in addition to cGMP, other nucleoside 3',5'-cyclic monophosphates (cNMPs) are synthesized by sGC in response to nitric oxide stimulation, and some of these nucleoside 3',5'-cyclic monophosphates are involved in various physiological activities. For example, inosine 3',5'-cyclic monophosphate synthesized by sGC may play a critical role in hypoxic augmentation of vasoconstriction. The involvement of cytidine 3',5'-cyclic monophosphate and uridine 3',5'-cyclic monophosphate in certain cardiovascular activities is also implicated.

DNA methylation patterns and gene expression associated with litter size in Berkshire pig placenta

Increasing litter size is of great interest to the pig industry. DNA methylation is an important epigenetic modification that regulates gene expression, resulting in livestock phenotypes such as disease resistance, milk production, and reproduction. We classified Berkshire pigs into two groups according to litter size and estimated breeding value: smaller (SLG) and larger (LLG) litter size groups. Genome-wide DNA methylation and gene expression were analyzed using placenta genomic DNA and RNA to identify differentially methylated regions (DMRs) and differentially expressed genes (DEGs) associated with litter size. The methylation levels of CpG dinucleotides in different genomic regions were noticeably different between the groups, while global methylation pattern was similar, and excluding intergenic regions they were found the most frequently in gene body regions. Next, we analyzed RNA-Seq data to identify DEGs between the SLG and LLG groups. A total of 1591 DEGs were identified: 567 were downregulated and 1024 were upregulated in LLG compared to SLG. To identify genes that simultaneously exhibited changes in DNA methylation and mRNA expression, we integrated and analyzed the data from bisulfite-Seq and RNA-Seq. Nine DEGs positioned in DMRs were found. The expression of only three of these genes (PRKG2, CLCA4, and PCK1) was verified by RT-qPCR. Furthermore, we observed the same methylation patterns in blood samples as in the placental tissues by PCR-based methylation analysis. Together, these results provide useful data regarding potential epigenetic markers for selecting hyperprolific sows.

Bacterial Nucleotidyl Cyclase Inhibits the Host Innate Immune Response by Suppressing TAK1 Activation

Exoenzyme Y (ExoY) is a type III secretion system effector found in 90% of the Pseudomonas aeruginosa isolates. Although it is known that ExoY is a soluble nucleotidyl cyclase that increases the cytoplasmic levels of nucleoside 3',5'-cyclic monophosphates (cNMPs) to mediate endothelial Tau phosphorylation and permeability, its functional role in the innate immune response is still poorly understood. Transforming growth factor β-activated kinase 1 (TAK1) is critical for mediating Toll-like receptor (TLR) signaling and subsequent activation of NF-κB and AP-1, which are transcriptional activators of innate immunity. Here, we report that ExoY inhibits proinflammatory cytokine production through suppressing the activation of TAK1 as well as downstream NF-κB and mitogen-activated protein (MAP) kinases. Mice infected with ExoY-deficient P. aeruginosa had higher levels of tumor necrosis factor (TNF) and interleukin-6 (IL-6), more neutrophil recruitment, and a lower bacterial load in lung tissue than mice infected with wild-type P. aeruginosa Taken together, our findings identify a previously unknown mechanism by which P. aeruginosa ExoY inhibits the host innate immune response.

Unique aspects of the developing lung circulation: structural development and regulation of vasomotor tone

This review summarizes our current knowledge on lung vasculogenesis and angiogenesis during normal lung development and the regulation of fetal and postnatal pulmonary vascular tone. In comparison to that of the adult, the pulmonary circulation of the fetus and newborn displays many unique characteristics. Moreover, altered development of pulmonary vasculature plays a more prominent role in compromised pulmonary vasoreactivity than in the adult. Clinically, a better understanding of the developmental changes in pulmonary vasculature and vasomotor tone and the mechanisms that are disrupted in disease states can lead to the development of new therapies for lung diseases characterized by impaired alveolar structure and pulmonary hypertension.

Molecular Physiology of Membrane Guanylyl Cyclase Receptors

cGMP controls many cellular functions ranging from growth, viability, and differentiation to contractility, secretion, and ion transport. The mammalian genome encodes seven transmembrane guanylyl cyclases (GCs), GC-A to GC-G, which mainly modulate submembrane cGMP microdomains. These GCs share a unique topology comprising an extracellular domain, a short transmembrane region, and an intracellular COOH-terminal catalytic (cGMP synthesizing) region. GC-A mediates the endocrine effects of atrial and B-type natriuretic peptides regulating arterial blood pressure/volume and energy balance. GC-B is activated by C-type natriuretic peptide, stimulating endochondral ossification in autocrine way. GC-C mediates the paracrine effects of guanylins on intestinal ion transport and epithelial turnover. GC-E and GC-F are expressed in photoreceptor cells of the retina, and their activation by intracellular Ca(2+)-regulated proteins is essential for vision. Finally, in the rodent system two olfactorial GCs, GC-D and GC-G, are activated by low concentrations of CO2and by peptidergic (guanylins) and nonpeptidergic odorants as well as by coolness, which has implications for social behaviors. In the past years advances in human and mouse genetics as well as the development of sensitive biosensors monitoring the spatiotemporal dynamics of cGMP in living cells have provided novel relevant information about this receptor family. This increased our understanding of the mechanisms of signal transduction, regulation, and (dys)function of the membrane GCs, clarified their relevance for genetic and acquired diseases and, importantly, has revealed novel targets for therapies. The present review aims to illustrate these different features of membrane GCs and the main open questions in this field.

Extracellular purines' action on glomerular albumin permeability in isolated rat glomeruli: insights into the pathogenesis of albuminuria

Purinoceptors (adrengeric receptors and P2 receptors) are expressed on the cellular components of the glomerular filtration barrier, and their activation may affect glomerular permeability to albumin, which may ultimately lead to albuminuria, a well-established risk factor for the progression of chronic kidney disease and development of cardiovascular diseases. We investigated the mechanisms underlying the in vitro and in vivo purinergic actions on glomerular filter permeability to albumin by measuring convectional albumin permeability (Palb) in a single isolated rat glomerulus based on the video microscopy method. Primary cultured rat podocytes were used for the analysis of Palb, cGMP accumulation, PKG-Iα dimerization, and immunofluorescence. In vitro, natural nucleotides (ATP, ADP, UTP, and UDP) and nonmetabolized ATP analogs (2-meSATP and ATP-γ-S) increased Palb in a time- and concentration-dependent manner. The effects were dependent on P2 receptor activation, nitric oxide synthase, and cytoplasmic guanylate cyclase. ATP analogs significantly increased Palb, cGMP accumulation, and subcortical actin reorganization in a PKG-dependent but nondimer-mediated route in cultured podocytes. In vivo, 2-meSATP and ATP-γ-S increased Palb but did not significantly affect urinary albumin excretion. Both agonists enhanced the clathrin-mediated endocytosis of albumin in podocytes. A product of adenine nucleotides hydrolysis, adenosine, increased the permeability of the glomerular barrier via adrenergic receptors in a dependent and independent manner. Our results suggest that the extracellular nucleotides that stimulate an increase of glomerular Palb involve nitric oxide synthase and cytoplasmic guanylate cyclase with actin reorganization in podocytes.

Causal network analysis of head and neck keloid tissue identifies potential master regulators

OBJECTIVES/HYPOTHESIS

To generate novel insights and hypotheses in keloid development from potential master regulators.

STUDY DESIGN

Prospective cohort.

METHODS

Six fresh keloid and six normal skin samples from 12 anonymous donors were used in a prospective cohort study. Genome-wide profiling was done previously on the cohort using the Infinium HumanMethylation450 BeadChip (Illumina, San Diego, CA). The 190 statistically significant CpG islands between keloid and normal tissue mapped to 152 genes (P < .05). The top 10 statistically significant genes (VAMP5, ACTR3C, GALNT3, KCNAB2, LRRC61, SCML4, SYNGR1, TNS1, PLEKHG5, PPP1R13-α, false discovery rate <.015) were uploaded into the Ingenuity Pathway Analysis software's Causal Network Analysis (QIAGEN, Redwood City, CA). To reflect expected gene expression direction in the context of methylation changes, the inverse of the methylation ratio from keloid versus normal tissue was used for the analysis. Causal Network Analysis identified disease-specific master regulator molecules based on downstream differentially expressed keloid-specific genes and expected directionality of expression (hypermethylated vs. hypomethylated).

RESULTS

Causal Network Analysis software identified four hierarchical networks that included four master regulators (pyroxamide, tributyrin, PRKG2, and PENK) and 19 intermediate regulators.

CONCLUSIONS

Causal Network Analysis of differentiated methylated gene data of keloid versus normal skin demonstrated four causal networks with four master regulators. These hierarchical networks suggest potential driver roles for their downstream keloid gene targets in the pathogenesis of the keloid phenotype, likely triggered due to perturbation/injury to normal tissue.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:E319-E324, 2016.

An emerging role of cGMP in the treatment of schizophrenia: A review

Schizophrenia is a progressive psychotic disorder with devastating effects on the broad aspects of human emotion, perception, thought, and psychosocial interactions. Although treatment with antipsychotic drugs, the mainstay in the treatment of schizophrenia, the large number of patients with schizophrenia respond poorly to the pharmacological and, the large number of patients with schizophrenia poorly respond to the pharmacological treatment. Although a variety of novel therapeutics have long been tested, to date, no drugs clinically efficacious for schizophrenia are available. The multiple lines of evidence strongly suggest that the modulation of cyclic guanosine monophosphate (cGMP) is a promising target in promoting the novel therapeutic strategies of schizophrenia beyond the "receptor-dependent" psychopharmacology. cGMP is modulated via regulating its synthesis by N-methyl-d-aspartate receptor (NMDAR) and nitric oxide (NO), which regulate guannylyl cyclase (GC), the enzyme producing cGMP. cGMP is also regulated by phosphodiesterase (PDE), the enzyme hydrolyzing cGMP. In this review, we critically evaluate the therapeutic potential of agents modulating cGMP activity by regulating cGMP synthesis including NMDAR enhancers, NO enhancers, NO inhibitors including minocycline with anti-inflammatory properties and PDE inhibitors in improving the negative, cognitive and positive symptoms of schizophrenia. We also discuss the possible mechanisms by which these agents produce therapeutic effects on schizophrenia including cGMP signaling pathways, oxidative stress, and neuroinflammation.

The mutational landscape of cutaneous T cell lymphoma and Sézary syndrome

Sézary syndrome is a leukemic and aggressive form of cutaneous T cell lymphoma (CTCL) resulting from the malignant transformation of skin-homing central memory CD4(+) T cells. Here we performed whole-exome sequencing of tumor-normal sample pairs from 25 patients with Sézary syndrome and 17 patients with other CTCLs. These analyses identified a distinctive pattern of somatic copy number alterations in Sézary syndrome, including highly prevalent chromosomal deletions involving the TP53, RB1, PTEN, DNMT3A and CDKN1B tumor suppressors. Mutation analysis identified a broad spectrum of somatic mutations in key genes involved in epigenetic regulation (TET2, CREBBP, KMT2D (MLL2), KMT2C (MLL3), BRD9, SMARCA4 and CHD3) and signaling, including MAPK1, BRAF, CARD11 and PRKG1 mutations driving increased MAPK, NF-κB and NFAT activity upon T cell receptor stimulation. Collectively, our findings provide new insights into the genetics of Sézary syndrome and CTCL and support the development of personalized therapies targeting key oncogenically activated signaling pathways for the treatment of these diseases.

Association between miR-181b and PKG 1 in myocardial hypertrophy and its clinical implications

The aim of this study was to explore the microRNA (miR)-181b expression in myocardial hypertrophy and to investigate its association with cGMP-dependent protein kinase type I (PKG 1) in an in vitro model. The miR-181b level in the peripheral blood was determined in patients with myocardial hypertrophy, and an in vitro model was established via phenylephrine (PE) treatment. Reverse transcription-quantitative polymerase chain reaction analysis and western blotting were performed to detect the expression levels of miR-181b, PKG 1 and hypertrophy-related genes. The results revealed that the expression of miR-181b was elevated in the peripheral blood of patients with myocardial hypertrophy, and this may have contributed to the pathology and progression of the disease. When the primary myocardial cells were treated with PE, microscopic observation and flow cytometry revealed significant hypertrophy. Furthermore, upregulation of myocardial hypertrophy-related genes, including β-myosin heavy chain, α-sarcomeric actinin and atrial natriuretic peptide, was observed. The miR-181b expression level in the PE-treated cells was elevated, while the mRNA and protein expression levels of PKG 1 were decreased, indicating a negative correlation between miR-181b and PKG 1 in myocardial hypertrophy. In addition, when the PE-treated primary myocardial cells were transfected with miR-181b inhibitor, the reduced PKG 1 expression was restored and the myocardial hypertrophy alleviated, as indicated by the reduced cellular sizes and decreased expression levels of the myocardial hypertrophy-related genes. In conclusion, miR-181b expression has been shown to be upregulated in myocardial hypertrophy, and this may play a role in the pathogenesis of the disease by regulating the expression of PKG 1. The present findings suggest that miR-181b is a promising molecular indicator for the clinical diagnosis and treatment of cardiac hypertrophy.

The Golgi apparatus regulates cGMP-dependent protein kinase I compartmentation and proteolysis

cGMP-dependent protein kinase I (PKGI) is an important effector of cGMP signaling that regulates vascular smooth muscle cell (SMC) phenotype and proliferation. PKGI has been detected in the perinuclear region of cells, and recent data indicate that proprotein convertases (PCs) typically resident in the Golgi apparatus (GA) can stimulate PKGI proteolysis and generate a kinase fragment that localizes to the nucleus and regulates gene expression. However, the role of the endomembrane system in PKGI compartmentation and processing is unknown. Here, we demonstrate that PKGI colocalizes with endoplasmic reticulum (ER), ER-Golgi intermediate compartment, GA cisterna, and trans-Golgi network proteins in pulmonary artery SMC and cell lines. Moreover, PKGI localizes with furin, a trans-Golgi network-resident PC known to cleave PKGI. ER protein transport influences PKGI localization because overexpression of a constitutively inactive Sar1 transgene caused PKGI retention in the ER. Additionally, PKGI appears to reside within the GA because PKGI immunoreactivity was determined to be resistant to cytosolic proteinase K treatment in live cells. The GA appears to play a role in PKGI proteolysis because overexpression of inositol 1,4,5-trisphosphate receptor-associated cGMP kinase substrate, not only tethered heterologous PKGI-β to the ER and decreased its localization to the GA, but also diminished PKGI proteolysis and nuclear translocation. Also, inhibiting intra-GA protein transport with monensin was observed to decrease PKGI cleavage. These studies detail a role for the endomembrane system in regulating PKGI compartmentation and proteolysis. Moreover, they support the investigation of mechanisms regulating PKGI-dependent nuclear cGMP signaling in the pulmonary vasculature with Golgi dysfunction.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

cGMP-dependent protein kinase I gamma encodes a nuclear localization signal that regulates nuclear compartmentation and function

cGMP-dependent protein kinase I (PKGI) plays an important role in regulating how cGMP specifies vascular smooth muscle cell (SMC) phenotype. Although studies indicate that PKGI nuclear localization controls how cGMP regulates gene expression in SMC, information about the mechanisms that regulate PKGI nuclear compartmentation and its role in directly regulating cell phenotype is limited. Here we characterize a nuclear localization signal sequence (NLS) in PKGIγ, a proteolytically cleaved PKGI kinase fragment that translocates to the nucleus of SMC. Immuno-localization studies using cells expressing native and NLS-mutant PKGIγ, and treated with a small molecule nuclear transport inhibitor, indicated that PKGIγ encodes a constitutively active NLS that requires importin α and β for regulation of its compartmentation. Moreover, studies utilizing a genetically encoded nuclear phospho-CREB biosensor probe and fluorescence lifetime imaging microscopy demonstrated that this NLS controls PKGIγ nuclear function. In addition, although cytosolic PKGIγ-activity was observed to stimulate MAPK/ERK-mediated nuclear CREB signaling in SMC, NLS-mediated PKGIγ nuclear activity alone was determined to increase the expression of differentiation marker proteins in these cells. These results indicate that NLS-mediated nuclear PKGIγ localization plays an important role in how PKGI regulates vascular SMC phenotype.

Phosphodiesterases and adrenal Cushing in mice and humans

The majority of benign adrenal cortex lesions leading to Cushing syndrome are associated to one or another abnormality of the cAMP/cGMP-phosphodiesterase signaling pathway. Phosphodiesterases (PDEs) are key regulatory enzymes of intracellular cAMP/cGMP levels. These second messengers play important regulatory roles in controlling steroidogenesis in the adrenal. Disruption of PDEs has been associated with a number of adrenal diseases. Specifically, genetic mutations have been associated with benign adrenal lesions, leading to Cushing syndrome and/or related adrenal hyperplasias. A Genome Wide Association study, in 2006, led to the identification of mutations in 2 PDE genes: PDE8B and PDE11A; mutations in these 2 genes modulate steroidogenesis. Further human studies have identified PDE2 as also directly regulating steroidogenesis. PDE2 decreases aldosterone production. This review focuses on the most recent knowledge we have gained on PDEs and their association with adrenal steroidogenesis and altered function, through analysis of patient cohorts and what we have learned from mouse studies.

Human exosomal placenta-associated miR-517a-3p modulates the expression of PRKG1 mRNA in Jurkat cells

During pregnancy, human placenta-associated microRNAs (miRNAs) derived from the miRNA cluster in human chromosome 19 are expressed in villous trophoblasts and secreted into maternal circulation via exosomes; however, little is known about whether circulating placenta-associated miRNAs are transferred into maternal immune cells via exosomes, and modulate expression of target genes in the recipient cells. We employed an in vitro model of trophoblast-immune cell communication using BeWo cells (a human trophoblast cell line) and Jurkat cells (a human leukemic T-cell line) and investigated whether BeWo exosomal placenta-associated miRNAs can suppress expression of target genes in the recipient Jurkat cells. Using this system, we identified PRKG1 as a target gene of placenta-associated miRNA miR-517a-3p. Moreover, we demonstrated that BeWo exosomal miR-517a-3p was internalized into Jurkat cells and subsequently suppressed the expression of PRKG1 in recipient Jurkat cells. Furthermore, using peripheral blood natural killer (NK) cells in vivo, we confirmed that circulating miR-517a-3p was delivered into maternal NK cells as it was into Jurkat cells in vitro. Placenta-associated miR-517a-3p was incorporated into maternal NK cells in the third trimester, and it was rapidly cleared after delivery. Expression levels of miR-517a-3p and its target mRNA PRKG1 were inversely correlated in NK cells before and after delivery. These in vitro and in vivo results suggest that exosome-mediated transfer of placenta-associated miRNAs and subsequent modulation of their target genes occur in maternal NK cells. The present study provides novel insight into our understanding of placenta-maternal communication.

NO/cGMP: the past, the present, and the future

The NO/cGMP signalling cascade participates in the regulation of physiological parameters such as smooth muscle relaxation, inhibition of platelet aggregation, and neuronal transmission. cGMP is formed in response to nitric oxide (NO) by NO-sensitive guanylyl cyclases that exist in two isoforms (NO-GC1 and NO-GC2). Much has been learned about the regulation of NO-GC; however the precise role of cGMP in complex physiological and especially in pathophysiological settings and its alteration by biological factors needs to be established. Despite reports on a variety of cGMP-independent NO effects, KO mice with a complete lack of NO-GC provide evidence that the vasorelaxing and platelet-inhibiting effects of NO are solely mediated by NO-GC. Isoform-specific KOs demonstrate that low cGMP increases are sufficient to induce smooth muscle relaxation and that either NO-GC isoform is sufficient in most instances outside the central nervous system. In the neuronal system, however, the NO-GC isoforms obviously serve distinct functions as both isoforms are required for long-term potentiation and NO-GC1 was shown to enhance glutamate release in excitatory neurons in the hippocampal CA1 region by gating HCN channels. Future studies have to clarify the role of NO-GC2, to show whether HCN channels are general targets of cGMP in the nervous system and whether the NO/cGMP signalling cascade participates in synaptic transmission in other brain regions.