Human model of primary carnitine deficiency cardiomyopathy reveals ferroptosis as a novel mechanism

Primary carnitine deficiency (PCD) is an autosomal recessive monogenic disorder caused by mutations in SLC22A5. This gene encodes for OCTN2, which transports the essential metabolite carnitine into the cell. PCD patients suffer from muscular weakness and dilated cardiomyopathy. Two OCTN2-defective human induced pluripotent stem cell lines were generated, carrying a full OCTN2 knockout and a homozygous OCTN2 (N32S) loss-of-function mutation. OCTN2-defective genotypes showed lower force development and resting length in engineered heart tissue format compared with isogenic control. Force was sensitive to fatty acid-based media and associated with lipid accumulation, mitochondrial alteration, higher glucose uptake, and metabolic remodeling, replicating findings in animal models. The concordant results of OCTN2 (N32S) and -knockout emphasizes the relevance of OCTN2 for these findings. Importantly, genome-wide analysis and pharmacological inhibitor experiments identified ferroptosis, an iron- and lipid-dependent cell death pathway associated with fibroblast activation as a novel PCD cardiomyopathy disease mechanism.

A Carboxy-terminal Smarcb1 Point Mutation Induces Hydrocephalus Formation and Affects AP-1 and Neuronal Signalling Pathways in Mice

The BAF (BRG1/BRM-associated factor) chromatin remodelling complex is essential for the regulation of DNA accessibility and gene expression during neuronal differentiation. Mutations of its core subunit SMARCB1 result in a broad spectrum of pathologies, including aggressive rhabdoid tumours or neurodevelopmental disorders. Other mouse models have addressed the influence of a homo- or heterozygous loss of Smarcb1, yet the impact of specific non-truncating mutations remains poorly understood. Here, we have established a new mouse model for the carboxy-terminal Smarcb1 c.1148del point mutation, which leads to the synthesis of elongated SMARCB1 proteins. We have investigated its impact on brain development in mice using magnetic resonance imaging, histology, and single-cell RNA sequencing. During adolescence, Smarcb11148del/1148del mice demonstrated rather slow weight gain and frequently developed hydrocephalus including enlarged lateral ventricles. In embryonic and neonatal stages, mutant brains did not differ anatomically and histologically from wild-type controls. Single-cell RNA sequencing of brains from newborn mutant mice revealed that a complete brain including all cell types of a physiologic mouse brain is formed despite the SMARCB1 mutation. However, neuronal signalling appeared disturbed in newborn mice, since genes of the AP-1 transcription factor family and neurite outgrowth-related transcripts were downregulated. These findings support the important role of SMARCB1 in neurodevelopment and extend the knowledge of different Smarcb1 mutations and their associated phenotypes.

CRISPR/Cas9 Knock-Out in Primary Neonatal and Adult Cardiomyocytes Reveals Distinct cAMP Dynamics Regulation by Various PDE2A and PDE3A Isoforms

Cyclic nucleotide phosphodiesterases 2A (PDE2A) and PDE3A play an important role in the regulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)-to-cAMP crosstalk. Each of these PDEs has up to three distinct isoforms. However, their specific contributions to cAMP dynamics are difficult to explore because it has been challenging to generate isoform-specific knock-out mice or cells using conventional methods. Here, we studied whether the CRISPR/Cas9 approach for precise genome editing can be used to knock out Pde2a and Pde3a genes and their distinct isoforms using adenoviral gene transfer in neonatal and adult rat cardiomyocytes. Cas9 and several specific gRNA constructs were cloned and introduced into adenoviral vectors. Primary adult and neonatal rat ventricular cardiomyocytes were transduced with different amounts of Cas9 adenovirus in combination with PDE2A or PDE3A gRNA constructs and cultured for up to 6 (adult) or 14 (neonatal) days to analyze PDE expression and live cell cAMP dynamics. A decline in mRNA expression for PDE2A (~80%) and PDE3A (~45%) was detected as soon as 3 days post transduction, with both PDEs being reduced at the protein level by >50-60% in neonatal cardiomyocytes (after 14 days) and >95% in adult cardiomyocytes (after 6 days). This correlated with the abrogated effects of selective PDE inhibitors in the live cell imaging experiments based on using cAMP biosensor measurements. Reverse transcription PCR analysis revealed that only the PDE2A2 isoform was expressed in neonatal myocytes, while adult cardiomyocytes expressed all three PDE2A isoforms (A1, A2, and A3) which contributed to the regulation of cAMP dynamics as detected by live cell imaging. In conclusion, CRISPR/Cas9 is an effective tool for the in vitro knock-out of PDEs and their specific isoforms in primary somatic cells. This novel approach suggests distinct regulation of live cell cAMP dynamics by various PDE2A and PDE3A isoforms in neonatal vs. adult cardiomyocytes.

Ablation of C-type natriuretic peptide/cGMP signaling in fibroblasts exacerbates adverse cardiac remodeling in mice

Excessive activation of cardiac fibroblasts (CFs) in response to injury provokes cardiac fibrosis, stiffness, and failure. The local mediators counter-regulating this response remain unclear. Exogenous C-type natriuretic peptide (CNP) exerted antifibrotic effects in preclinical models. To unravel the role of the endogenous hormone, we generated mice with fibroblast-restricted deletion (KO) of guanylyl cyclase-B (GC-B), the cGMP-synthesizing CNP receptor.CNP activated GC-B/cGMP signaling in human and murine CFs, preventing proliferative and promigratory effects of AngiotensinII (AngII) and TGF-β. Fibroblast-specific GC-B-KO mice showed enhanced fibrosis in response to AngII infusions. Moreover, after two weeks of mild pressure-overload induced by transverse aortic constriction (TAC), such KO mice had augmented cardiac fibrosis and hypertrophy, together with systolic and diastolic contractile dysfunction. This was associated with increased expression of the profibrotic genes collagen I, III and periostin. Notably, such responses to AngII and TAC were greater in female as compared to male KO mice. Enhanced AngII-induced CNP expression in female hearts and augmented GC-B expression and activity in female CFs may contribute to this sex disparity.The results show that paracrine CNP signaling in CFs has antifibrotic and antihypertrophic effects. The CNP/GC-B/cGMP pathway might be a target for therapies combating pathological cardiac remodeling.

Familial atrial fibrillation mutation M1875T-SCN5A increases early sodium current and dampens the effect of flecainide

AIMS

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Pathogenic variants in genes encoding ion channels are associated with familial AF. The point mutation M1875T in the SCN5A gene, which encodes the α-subunit of the cardiac sodium channel Nav1.5, has been associated with increased atrial excitability and familial AF in patients.

METHODS AND RESULTS

We designed a new murine model carrying the Scn5a-M1875T mutation enabling us to study the effects of the Nav1.5 mutation in detail in vivo and in vitro using patch clamp and microelectrode recording of atrial cardiomyocytes, optical mapping, electrocardiogram, echocardiography, gravimetry, histology, and biochemistry. Atrial cardiomyocytes from newly generated adult Scn5a-M1875T+/- mice showed a selective increase in the early (peak) cardiac sodium current, larger action potential amplitude, and a faster peak upstroke velocity. Conduction slowing caused by the sodium channel blocker flecainide was less pronounced in Scn5a-M1875T+/- compared to wildtype atria. Overt hypertrophy or heart failure in Scn5a-M1875T+/- mice could be excluded.

CONCLUSION

The Scn5a-M1875T point mutation causes gain-of-function of the cardiac sodium channel. Our results suggest increased atrial peak sodium current as a potential trigger for increased atrial excitability.

Impaired myocellular Ca2+ cycling in protein phosphatase PP2A-B56α knockout mice is normalized by β-adrenergic stimulation

The activity of protein phosphatase 2A (PP2A) is determined by the expression and localization of the regulatory B-subunits. PP2A-B56α is the dominant isoform of the B′-family in the heart. Its role in regulating the cardiac response to β-adrenergic stimulation is not yet fully understood. We therefore generated mice deficient in B56α to test the functional cardiac effects in response to catecholamine administration versus corresponding WT mice. We found the decrease in basal PP2A activity in hearts of KO mice was accompanied by a counter-regulatory increase in the expression of B′ subunits (β and γ) and higher phosphorylation of sarcoplasmic reticulum Ca²⁺ regulatory and myofilament proteins. The higher phosphorylation levels were associated with enhanced intraventricular pressure and relaxation in catheterized KO mice. In contrast, at the cellular level, we detected depressed Ca²⁺ transient and sarcomere shortening parameters in KO mice at basal conditions. Consistently, the peak amplitude of the L-type Ca²⁺ current was reduced and the inactivation kinetics of I_CaL were prolonged in KO cardiomyocytes. However, we show β-adrenergic stimulation resulted in a comparable peak amplitude of Ca²⁺ transients and myocellular contraction between KO and WT cardiomyocytes. Therefore, we propose higher isoprenaline-induced Ca²⁺ spark frequencies might facilitate the normalized Ca²⁺ signaling in KO cardiomyocytes. In addition, the application of isoprenaline was associated with unchanged L-type Ca²⁺ current parameters between both groups. Our data suggest an important influence of PP2A-B56α on the regulation of Ca²⁺ signaling and contractility in response to β-adrenergic stimulation in the myocardium.

Rise of cGMP by partial phosphodiesterase-3A degradation enhances cardioprotection during hypoxia

3',5'-cyclic guanosine monophosphate (cGMP) is a druggable second messenger regulating cell growth and survival in a plethora of cells and disease states, many of which are associated with hypoxia. For example, in myocardial infarction and heart failure (HF), clinical use of cGMP-elevating drugs improves disease outcomes. Although they protect mice from ischemia/reperfusion (I/R) injury, the exact mechanism how cardiac cGMP signaling is regulated in response to hypoxia is still largely unknown. By monitoring real-time cGMP dynamics in murine and human cardiomyocytes using in vitro and in vivo models of hypoxia/reoxygenation (H/R) and I/R injury combined with biochemical methods, we show that hypoxia causes rapid but partial degradation of cGMP-hydrolyzing phosphodiesterase-3A (PDE3A) protein via the autophagosomal-lysosomal pathway. While increasing cGMP in hypoxia prevents cell death, partially reduced PDE3A does not change the pro-apoptotic second messenger 3',5'-cyclic adenosine monophosphate (cAMP). However, it leads to significantly enhanced protective effects of clinically relevant activators of nitric oxide-sensitive guanylyl cyclase (NO-GC). Collectively, our mouse and human data unravel a new mechanism by which cardiac cGMP improves hypoxia-associated disease conditions.

The SCN5A point mutation M1875T, associated with familial atrial fibrillation, causes a gain-of-function effect of the cardiac Nav1.5 channel in atrial cardiomyocytes

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Leducq Foundation

Background

The point mutation M1875T in the SCN5A gene, which encodes the pore-forming α-subunit of the cardiac voltage-gated Na+ channel Nav1.5, has been associated with familial atrial fibrillation (AF), but its effects on atrial cardiomyocyte electrophysiology is unclear.

Aim

To investigate the effect of the point mutation M1875T on atrial electrophysiological parameters.

Methods

In a novel heterozygous knock-in murine model (Scn5a-M1875T+/-), whole-cell patch clamp electrophysiology was used to investigate Na+ currents in left atrial (LA) cardiomyocytes isolated from hearts of young adult mice (10-16 weeks). LA microelectrode and optical mapping recordings were used to study action potential (AP) characteristics. Cardiac size and function were measured by transthoracic echocardiography. Atrial Scn5a gene and Nav1.5 protein expression were assessed by Rt-PCR and Western blot.

Results

The Na+ current was increased in cardiomyocytes isolated from Scn5a-M1875T+/- LA (wildtype (WT) -22.7 ± 0.9 pA/pF (N = 14, n = 115); Scn5a-M1875T+/- -28.3 ± 1.1 pA/pF (N = 15, n = 117)). Scn5a-M1875T+/- intact isolated superfused LA had an elevated AP amplitude (100 ms pacing cycle length (PCL): WT 86.4 ± 0.9 mV (N = 8, n = 24); Scn5a-M1875T+/- 91.2 ± 0.7 mV (N = 8, n = 25)) and a faster peak upstroke velocity (100 ms PCL: WT 127.98 ± 3.28 mV/ms; Scn5a-M1875T+/- 142.80 ± 3.98 mV/ms). AP duration (APD) was not different apart from a small APD shortening at slow rates. Echocardiography revealed no difference in size and function at the age of investigation. Atrial Scn5a gene and Nav1.5 protein expression were comparable. When challenged with flecainide (1 µM), Scn5a-M1875T+/- LA showed less conduction slowing than WT (100 ms PCL: WT -10.43 ± 1.27 cm/s (N = 12); Scn5a-M1875T+/- -6.10 ± 1.34 cm/s (N = 12)).  5 µM flecainide caused significant increase in WT refractoriness (7/12 atria lost 1:1 capture at PCL ≤ 120 ms) compared to Scn5a-M1875T+/- (1/12).

Conclusion(s): SCN5A point mutation M1875T increases the Na+ current in atrial cardiomyocytes and intact atria, leading to a faster AP upstroke and an attenuated response to flecainide. Abstract Figure 1: Current-Voltage relationship

A Comprehensive Review of Genetically Engineered Mouse Models for Prader-Willi Syndrome Research

Prader-Willi syndrome (PWS) is a neurogenetic multifactorial disorder caused by the deletion or inactivation of paternally imprinted genes on human chromosome 15q11-q13. The affected homologous locus is on mouse chromosome 7C. The positional conservation and organization of genes including the imprinting pattern between mice and men implies similar physiological functions of this locus. Therefore, considerable efforts to recreate the pathogenesis of PWS have been accomplished in mouse models. We provide a summary of different mouse models that were generated for the analysis of PWS and discuss their impact on our current understanding of corresponding genes, their putative functions and the pathogenesis of PWS. Murine models of PWS unveiled the contribution of each affected gene to this multi-facetted disease, and also enabled the establishment of the minimal critical genomic region (PWScr) responsible for core symptoms, highlighting the importance of non-protein coding genes in the PWS locus. Although the underlying disease-causing mechanisms of PWS remain widely unresolved and existing mouse models do not fully capture the entire spectrum of the human PWS disorder, continuous improvements of genetically engineered mouse models have proven to be very powerful and valuable tools in PWS research.

TrkC Is Essential for Nephron Function and Trans-Activates Igf1R Signaling

BACKGROUND

Injury to kidney podocytes often results in chronic glomerular disease and consecutive nephron malfunction. For most glomerular diseases, targeted therapies are lacking. Thus, it is important to identify novel signaling pathways contributing to glomerular disease. Neurotrophic tyrosine kinase receptor 3 (TrkC) is expressed in podocytes and the protein transmits signals to the podocyte actin cytoskeleton.

METHODS

Nephron-specific TrkC knockout (TrkC-KO) and nephron-specific TrkC-overexpressing (TrkC-OE) mice were generated to dissect the role of TrkC in nephron development and maintenance.

RESULTS

Both TrkC-KO and TrkC-OE mice exhibited enlarged glomeruli, mesangial proliferation, basement membrane thickening, albuminuria, podocyte loss, and aspects of FSGS during aging. Igf1 receptor (Igf1R)-associated gene expression was dysregulated in TrkC-KO mouse glomeruli. Phosphoproteins associated with insulin, erb-b2 receptor tyrosine kinase (Erbb), and Toll-like receptor signaling were enriched in lysates of podocytes treated with the TrkC ligand neurotrophin-3 (Nt-3). Activation of TrkC by Nt-3 resulted in phosphorylation of the Igf1R on activating tyrosine residues in podocytes. Igf1R phosphorylation was increased in TrkC-OE mouse kidneys while it was decreased in TrkC-KO kidneys. Furthermore, TrkC expression was elevated in glomerular tissue of patients with diabetic kidney disease compared with control glomerular tissue.

CONCLUSIONS

Our results show that TrkC is essential for maintaining glomerular integrity. Furthermore, TrkC modulates Igf-related signaling in podocytes.

A paradoxical increase of force development in saphenous and tail arteries from heterozygous ANO1 knockout mice

A Ca²⁺‐activated Cl⁻ channel protein, ANO1, is expressed in vascular smooth muscle cells where Cl⁻ current is thought to potentiate contraction by contributing to membrane depolarization. However, there is an inconsistency between previous knockout and knockdown studies on ANO1’s role in small arteries. In this study, we assessed cardiovascular function of heterozygous mice with global deletion of exon 7 in the ANO1 gene. We found decreased expression of ANO1 in aorta, saphenous and tail arteries from heterozygous ANO1 knockout mice in comparison with wild type. Accordingly, ANO1 knockdown reduced the Ca²⁺‐activated Cl⁻ current in smooth muscle cells. Consistent with conventional hypothesis, the contractility of aorta from ANO1 heterozygous mice was reduced. Surprisingly, we found an enhanced contractility of tail and saphenous arteries from ANO1 heterozygous mice when stimulated with noradrenaline, vasopressin, and K⁺‐induced depolarization. This difference was endothelium‐independent. The increased contractility of ANO1 downregulated small arteries was due to increased Ca²⁺ influx. The expression of L‐type Ca²⁺ channels was not affected but expression of the plasma membrane Ca²⁺ ATPase 1 and the Piezo1 channel was increased. Expressional analysis of tail arteries further suggested changes of ANO1 knockdown smooth muscle cells toward a pro‐contractile phenotype. We did not find any difference between genotypes in blood pressure, heart rate, pressor response, and vasorelaxation in vivo. Our findings in tail and saphenous arteries contrast with the conventional hypothesis and suggest additional roles for ANO1 as a multifunctional protein in the vascular wall that regulates Ca²⁺ homeostasis and smooth muscle cell phenotype.

C-type natriuretic peptide moderates titin-based cardiomyocyte stiffness

Heart failure is often accompanied by titin-dependent myocardial stiffness. Phosphorylation of titin by cGMP-dependent protein kinase I (PKGI) increases cardiomyocyte distensibility. The upstream pathways stimulating PKGI-mediated titin phosphorylation are unclear. We studied whether C-type natriuretic peptide (CNP), via its guanylyl cyclase-B (GC-B) receptor and cGMP/PKGI signaling, modulates titin-based ventricular compliance. To dissect GC-B–mediated effects of endogenous CNP in cardiomyocytes, we generated mice with cardiomyocyte-restricted GC-B deletion (CM GC-B–KO mice). The impact on heart morphology and function, myocyte passive tension, and titin isoform expression and phosphorylation was studied at baseline and after increased afterload induced by transverse aortic constriction (TAC). Pressure overload increased left ventricular endothelial CNP expression, with an early peak after 3 days. Concomitantly, titin phosphorylation at Ser₄₀₈₀, the site phosphorylated by PKGI, was augmented. Notably, in CM GC-B–KO mice this titin response was abolished. TAC-induced hypertrophy and fibrosis were not different between genotypes. However, the KO mice presented mild systolic and diastolic dysfunction together with myocyte stiffness, which were not observed in control littermates. In vitro, recombinant PKGI rescued reduced titin-Ser₄₀₈₀ phosphorylation and reverted passive stiffness of GC-B–deficient cardiomyocytes. CNP-induced activation of GC-B/cGMP/PKGI signaling in cardiomyocytes provides a protecting regulatory circuit preventing titin-based myocyte stiffening during early phases of pressure overload.

C-type natriuretic peptide via GC-B/cGMP/PKGI signalling in cardiomyocytes attenuates titin-based cardiomyocyte stiffening during early phases of pressure-overload.

Circular RNA Encoded Amyloid Beta peptides-A Novel Putative Player in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related detrimental dementia. Amyloid beta peptides (Aβ) play a crucial role in the pathology of AD. In familial AD, Aβ are generated from the full-length amyloid beta precursor protein (APP) via dysregulated proteolytic processing; however, in the case of sporadic AD, the mechanism of Aβ biogenesis remains elusive. circRNAs are a class of transcripts preferentially expressed in brain. We identified a circRNA harboring the Aβ-coding region of the APP gene termed circAβ-a. This circular RNA was detected in the brains of AD patients and non-dementia controls. With the aid of our recently established approach for analysis of circRNA functions, we demonstrated that circAβ-a is efficiently translated into a novel Aβ-containing Aβ175 polypeptide (19.2 KDa) in both cultured cells and human brain. Furthermore, Aβ175 was shown to be processed into Aβ peptides-a hallmark of AD. In summary, our analysis revealed an alternative pathway of Aβ biogenesis. Consequently, circAβ-a and its corresponding translation product could potentially represent novel therapeutic targets for AD treatment. Importantly, our data point to yet another evolutionary route for potentially increasing proteome complexity by generating additional polypeptide variants using back-splicing of primary transcripts that yield circular RNA templates.

The Receptor for Advanced Glycation Endproducts (RAGE) Contributes to Severe Inflammatory Liver Injury in Mice

Background: The receptor for advanced glycation end products (RAGE) is a multiligand receptor involved in a number of processes and disorders. While it is known that RAGE-signaling can contribute to toxic liver damage and fibrosis, its role in acute inflammatory liver injury and septic multiorgan failure is yet undefined. We examined RAGE in lipopolysaccharide (LPS) induced acute liver injury of D-galN sensitized mice as a classical model for tumor necrosis factor alpha (TNF-α) dependent inflammatory organ damage.

Methods: Mice (Rage–/– and C57BL/6) were intraperitoneally injected with D-galN (300 mg/kg) and LPS (10 μg/kg). Animals were monitored clinically, and cytokines, damage associated molecular pattern molecules (DAMPs) as well as liver enzymes were determined in serum. Liver histology, hepatic cytokines as well as RAGE mRNA expression were analyzed. Cellular activation and functionality were evaluated by flow cytometry both in bone marrow- and liver-derived cells.

Results: Genetic deficiency of RAGE significantly reduced the mortality of mice exposed to LPS/D-galN. Hepatocyte damage markers were reduced in Rage–/– mice, and liver histopathology was less severe. Rage–/– mice produced less pro-inflammatory cytokines and DAMPs in serum and liver. While immune cell functions appeared normal, TNF-α production by hepatocytes was reduced in Rage–/– mice.

Conclusions: We found that RAGE deletion attenuated the expression of pro-inflammatory cytokines and DAMPs in hepatocytes without affecting cellular immune functions in the LPS/D-galN model of murine liver injury. Our data highlight the importance of tissue-specific RAGE-signaling also in acute inflammatory liver stress contributing to sepsis and multiorgan failure.

DNA barcoding reveals that injected transgenes are predominantly processed by homologous recombination in mouse zygote

Mechanisms that ensure repair of double-strand DNA breaks (DSBs) are instrumental in the integration of foreign DNA into the genome of transgenic organisms. After pronuclear microinjection, exogenous DNA is usually found as a concatemer comprising multiple co-integrated transgene copies. Here, we investigated the contribution of various DSB repair pathways to the concatemer formation. We injected mouse zygotes with a pool of linear DNA molecules carrying unique barcodes at both ends and obtained 10 transgenic embryos with 1–300 transgene copies. Sequencing the barcodes allowed us to assign relative positions to the copies in concatemers and detect recombination events that occurred during integration. Cumulative analysis of approximately 1,000 integrated copies reveals that over 80% of them underwent recombination when their linear ends were processed by synthesis-dependent strand annealing (SDSA) or double-strand break repair (DSBR). We also observed evidence of double Holliday junction (dHJ) formation and crossing over during the concatemer formations. Sequencing indels at the junctions between copies shows that at least 10% of DNA molecules introduced into the zygotes are ligated by non-homologous end joining (NHEJ). Our barcoding approach, verified with Pacific Biosciences Single Molecule Real-Time (SMRT) long-range sequencing, documents high activity of homologous recombination after DNA microinjection.

DHHC7-mediated palmitoylation of the accessory protein barttin critically regulates the functions of ClC-K chloride channels

Barttin is the accessory subunit of the human ClC-K chloride channels, which are expressed in both the kidney and inner ear. Barttin promotes trafficking of the complex it forms with ClC-K to the plasma membrane and is involved in activating this channel. Barttin undergoes post-translational palmitoylation that is essential for its functions, but the enzyme(s) catalyzing this post-translational modification is unknown. Here, we identified zinc finger DHHC-type containing 7 (DHHC7) protein as an important barttin palmitoyl acyltransferase, whose depletion affected barttin palmitoylation and ClC-K-barttin channel activation. We investigated the functional role of barttin palmitoylation in vivo in Zdhhc7 ^-/- mice. Although palmitoylation of barttin in kidneys of Zdhhc7 ^-/- animals was significantly decreased, it did not pathologically alter kidney structure and functions under physiological conditions. However, when Zdhhc7 ^-/- mice were fed a low-salt diet, they developed hyponatremia and mild metabolic alkalosis, symptoms characteristic of human Bartter syndrome (BS) type IV. Of note, we also observed decreased palmitoylation of the disease-causing R8L barttin variant associated with human BS type IV. Our results indicate that dysregulated DHHC7-mediated barttin palmitoylation appears to play an important role in chloride channel dysfunction in certain BS variants, suggesting that targeting DHHC7 activity may offer a potential therapeutic strategy for reducing hypertension.

Pervasive head-to-tail insertions of DNA templates mask desired CRISPR-Cas9-mediated genome editing events

CRISPR-Cas9-mediated homology-directed DNA repair is the method of choice for precise gene editing in a wide range of model organisms, including mouse and human. Broad use by the biomedical community refined the method, making it more efficient and sequence specific. Nevertheless, the rapidly evolving technique still contains pitfalls. During the generation of six different conditional knockout mouse models, we discovered that frequently (sometimes solely) homology-directed repair and/or nonhomologous end joining mechanisms caused multiple unwanted head-to-tail insertions of donor DNA templates. Disturbingly, conventionally applied PCR analysis, in most cases, failed to identify these multiple integration events, which led to a high rate of falsely claimed precisely edited alleles. We caution that comprehensive analysis of modified alleles is essential and offer practical solutions to correctly identify precisely edited chromosomes.

Endothelial C-Type Natriuretic Peptide Acts on Pericytes to Regulate Microcirculatory Flow and Blood Pressure

BACKGROUND

Peripheral vascular resistance has a major impact on arterial blood pressure levels. Endothelial C-type natriuretic peptide (CNP) participates in the local regulation of vascular tone, but the target cells remain controversial. The cGMP-producing guanylyl cyclase-B (GC-B) receptor for CNP is expressed in vascular smooth muscle cells (SMCs). However, whereas endothelial cell-specific CNP knockout mice are hypertensive, mice with deletion of GC-B in vascular SMCs have unaltered blood pressure.

METHODS

We analyzed whether the vasodilating response to CNP changes along the vascular tree, ie, whether the GC-B receptor is expressed in microvascular types of cells. Mice with a floxed GC-B ( Npr2) gene were interbred with Tie2-Cre or PDGF-Rβ-Cre ^ERT2 lines to develop mice lacking GC-B in endothelial cells or in precapillary arteriolar SMCs and capillary pericytes. Intravital microscopy, invasive and noninvasive hemodynamics, fluorescence energy transfer studies of pericyte cAMP levels in situ, and renal physiology were combined to dissect whether and how CNP/GC-B/cGMP signaling modulates microcirculatory tone and blood pressure.

RESULTS

Intravital microscopy studies revealed that the vasodilatatory effect of CNP increases toward small-diameter arterioles and capillaries. CNP consistently did not prevent endothelin-1-induced acute constrictions of proximal arterioles, but fully reversed endothelin effects in precapillary arterioles and capillaries. Here, the GC-B receptor is expressed both in endothelial and mural cells, ie, in pericytes. It is notable that the vasodilatatory effects of CNP were preserved in mice with endothelial GC-B deletion, but abolished in mice lacking GC-B in microcirculatory SMCs and pericytes. CNP, via GC-B/cGMP signaling, modulates 2 signaling cascades in pericytes: it activates cGMP-dependent protein kinase I to phosphorylate downstream targets such as the cytoskeleton-associated vasodilator-activated phosphoprotein, and it inhibits phosphodiesterase 3A, thereby enhancing pericyte cAMP levels. These pathways ultimately prevent endothelin-induced increases of pericyte calcium levels and pericyte contraction. Mice with deletion of GC-B in microcirculatory SMCs and pericytes have elevated peripheral resistance and chronic arterial hypertension without a change in renal function.

CONCLUSIONS

Our studies indicate that endothelial CNP regulates distal arteriolar and capillary blood flow. CNP-induced GC-B/cGMP signaling in microvascular SMCs and pericytes is essential for the maintenance of normal microvascular resistance and blood pressure.

A universal approach to investigate circRNA protein coding function

Circular RNAs (circRNAs) are an emerging class of RNA molecules that have been linked to human diseases and important regulatory pathways. Their functional roles are still under investigation, often hampered by inefficient circRNA formation in and ex vivo. We generated an intron-mediated enhancement (IME) system that-in comparison to previously published methods-increases circRNA formation up to 5-fold. This strategy also revealed previously undetected translation of circRNA, e.g., circRtn4. Substantiated by Western blots and mass spectrometry we showed that in mammalian cells, translation of circRtn4 containing a potential "infinite" circular reading frame resulted in "monomers" and extended proteins, presumably "multimer" tandem repeats. In order to achieve high levels of circRNA formation and translation of other natural or recombinant circRNAs, we constructed a versatile circRNA expression vector-pCircRNA-DMo. We demonstrated the general applicability of this method by efficiently generating two additional circRNAs exhibiting high expression levels. The circRNA expression vector will be an important tool to investigate different aspects of circRNA biogenesis and to gain insights into mechanisms of circular RNA translation.

A simple method for in-house Pfu DNA polymerase purification for high-fidelity PCR amplification

  Background and Objectives: Pfu DNA polymerase is an enzyme that exhibits the lowest error rate in the 3´ to 5´ exonucle- ase (proofreading) activity during DNA synthesis in Polymerase Chain Reactions (PCRs). This study was aimed to express and purify Pfu DNA polymerase in a bacterial expression system under a simple purification method. Materials and Methods: Pfu polymerase gene sequence, derived from Pyrocuccus furiosus (Pfu) genomic DNA, was cloned and overexpressed in E. coli BL21 (DE3) pLysS. Upon overexpression, bacterial lysate containing the Pfu DNA polymerase was heated at 94°C for 5 minutes. Pfu DNA polymerase having high thermal stability was retained while the other bacterial proteins were denatured. The resulting thermo stable Pfu DNA polymerase was separated from the other debris of the dena- tured proteins by simple centrifugation. Results: The enzymatic activity of the resulting Pfu DNA polymerase was estimated by comparing with the commer- cial Pfu DNA Polymerases. An estimated 50000 units of functional Pfu DNA polymerase was produced from a 400 ml culture. Conclusion: The in-house produced Pfu DNA Polymerase could be used for routine amplification that requires high-fidelity such as cloning and DNA sequencing.

A simple method for in-house Pfu DNA polymerase purification for high-fidelity PCR amplification

BACKGROUND AND OBJECTIVES

Pfu DNA polymerase is an enzyme that exhibits the lowest error rate in the 3' to 5' exonuclease (proofreading) activity during DNA synthesis in Polymerase Chain Reactions (PCRs). This study was aimed to express and purify Pfu DNA polymerase in a bacterial expression system under a simple purification method.

MATERIALS AND METHODS

Pfu polymerase gene sequence, derived from Pyrocuccus furiosus (Pfu) genomic DNA, was cloned and overexpressed in E. coli BL21 (DE3) pLysS. Upon overexpression, bacterial lysate containing the Pfu DNA polymerase was heated at 94°C for 5 minutes. Pfu DNA polymerase having high thermal stability was retained while the other bacterial proteins were denatured. The resulting thermo stable Pfu DNA polymerase was separated from the other debris of the denatured proteins by simple centrifugation.

RESULTS

The enzymatic activity of the resulting Pfu DNA polymerase was estimated by comparing with the commercial Pfu DNA Polymerases. An estimated 50000 units of functional Pfu DNA polymerase was produced from a 400 ml culture.

CONCLUSION

The in-house produced Pfu DNA Polymerase could be used for routine amplification that requires high-fidelity such as cloning and DNA sequencing.

A novel isoform of myosin 18A (Myo18Aγ) is an essential sarcomeric protein in mouse heart

Whereas myosin 18B (Myo18B) is known to be a critical sarcomeric protein, the function of myosin 18A (Myo18A) is unclear, although it has been implicated in cell motility and Golgi shape. Here, we show that homozygous deletion (homozygous tm1a, tm1b, or tm1d alleles) of Myo18a in mouse is embryonic lethal. Reminiscent of Myo18b, Myo18a was highly expressed in the embryo heart, and cardiac-restricted Myo18a deletion in mice was embryonic lethal. Surprisingly, using Western blot analysis, we were unable to detect the known isoforms of Myo18A, Myo18Aα and Myo18Aβ, in mouse heart using a custom C-terminal antibody. However, alternative anti-Myo18A antibodies detected a larger than expected protein, and RNA-Seq analysis indicated that a novel Myo18A transcript is expressed in mouse ventricular myocytes (and human heart). Cloning and sequencing revealed that this cardiac isoform, denoted Myo18Aγ, lacks the PDZ-containing N terminus of Myo18Aα but includes an alternative N-terminal extension and a long serine-rich C terminus. EGFP-tagged Myo18Aγ expressed in ventricular myocytes localized to the level of A-bands in sarcomeres, and Myo18a knockout embryos at day 10.5 exhibited disorganized sarcomeres with wavy thick filaments. We additionally generated myeloid-restricted Myo18a knockout mice to investigate the role of Myo18A in nonmuscle cells, exemplified by macrophages, which express more Myo18Aβ than Myo18Aα, but no defects in cell shape, motility, or Golgi shape were detected. In summary, we have identified a previously unrecognized sarcomere component, a large novel isoform (denoted Myo18Aγ) of Myo18A. Thus, both members of class XVIII myosins are critical components of cardiac sarcomeres.

Phenotypic analysis of Myo10 knockout (Myo10tm2/tm2) mice lacking full-length (motorized) but not brain-specific headless myosin X

We investigated the physiological functions of Myo10 (myosin X) using Myo10 reporter knockout (Myo10tm2) mice. Full-length (motorized) Myo10 protein was deleted, but the brain-specific headless (Hdl) isoform (Hdl-Myo10) was still expressed in homozygous mutants. In vitro, we confirmed that Hdl-Myo10 does not induce filopodia, but it strongly localized to the plasma membrane independent of the MyTH4-FERM domain. Filopodia-inducing Myo10 is implicated in axon guidance and mice lacking the Myo10 cargo protein DCC (deleted in colorectal cancer) have severe commissural defects, whereas MRI (magnetic resonance imaging) of isolated brains revealed intact commissures in Myo10tm2/tm2 mice. However, reminiscent of Waardenburg syndrome, a neural crest disorder, Myo10tm2/tm2 mice exhibited pigmentation defects (white belly spots) and simple syndactyly with high penetrance (>95%), and 24% of mutant embryos developed exencephalus, a neural tube closure defect. Furthermore, Myo10tm2/tm2 mice consistently displayed bilateral persistence of the hyaloid vasculature, revealed by MRI and retinal whole-mount preparations. In principle, impaired tissue clearance could contribute to persistence of hyaloid vasculature and syndactyly. However, Myo10-deficient macrophages exhibited no defects in the phagocytosis of apoptotic or IgG-opsonized cells. RNA sequence analysis showed that Myo10 was the most strongly expressed unconventional myosin in retinal vascular endothelial cells and expression levels increased 4-fold between P6 and P15, when vertical sprouting angiogenesis gives rise to deeper layers. Nevertheless, imaging of isolated adult mutant retinas did not reveal vascularization defects. In summary, Myo10 is important for both prenatal (neural tube closure and digit formation) and postnatal development (hyaloid regression, but not retinal vascularization).

Nephron-specific knockin of the PIKfyve-binding-deficient Vac14L156R mutant results in albuminuria and mesangial expansion

Intracellular trafficking processes play a key role for the establishment and maintenance of membrane surfaces in renal epithelia. Therefore, dysfunctions of these trafficking processes could be key events and important determinants in the onset and progression of diseases. The presence of cellular vacuoles-observed in many histologic analyses of renal diseases-is a macroscopic hint for disturbed intracellular trafficking processes. However, how vacuoles develop and which intracellular pathways are directly affected remain largely unknown. Previous studies showed that in some cases, vacuolization is linked to malfunction of the Vac14 complex. This complex, including the scaffold protein Vac14, the lipid kinase PIKfyve, and its counteracting lipid phosphatase Fig4, regulates intracellular phosphatidylinositol phosphate levels, which in turn, control the maturation of early-into-late endosomes, as well as the processing of autophagosomes into autophagolysosomes. Here, we analyzed the role of Vac14 in mice and observed that the nephron-specific knockin of the PIKfyve-binding-deficient Vac14^L156R mutant led to albuminuria, accompanied by mesangial expansion, increased glomerular size, and an elevated expression of several kidney injury markers. Overexpression of this Vac14 variant in podocytes did not reveal a strong in vivo phenotype, indicating that Vac14-dependent trafficking processes are more important for tubular than for glomerular processes in the kidney. In vitro overexpression of Vac14^L156R in Madin-Darby canine kidney cells had no impact on apico-basal polarity defects but resulted in a faster reassembly of junctional structures after Ca²⁺ depletion and delayed endo- and transcytosis rates. Taken together, our data suggest that increased albuminuria of Vac14^L156R-overexpressing mice is a consequence of a lowered endo- and transcytosis of albumin in renal tubules.

Homozygous CREM-IbΔC-X Overexpressing Mice Are a Reliable and Effective Disease Model for Atrial Fibrillation

Background: Atrial fibrillation (AF) is a significant cause of morbidity and mortality with foreseeably increasing prevalence. While large animal models of the disease are well established but resource intensive, transgenic AF mouse models are not yet widely used to develop or validate novel therapeutics for AF. Hemizygous mice with a cardiomyocyte-specific overexpression of the human cAMP response element modulator (CREM) isoform IbΔC-X spontaneously develop AF on grounds of an arrhythmogenic substrate consisting of alterations in structure, conduction, and calcium handling.

Objective: We investigated if homozygous expression of the CREM-IbΔC-X transgene in mice alters the time course of AF development, and if homozygous CREM-IbΔC-X transgenics could be suitable as a disease model of AF.

Methods: Southern Blot, quantitative real-time PCR, and immunoblotting were used to identify and verify homozygous transgenics. Cardiac gravimetry, quantitative real-time RT-PCR, histology, survival analysis, and repeated ECG recordings allowed assessment of phenotypic development and effects of antiarrhythmic drugs.

Results: Homozygous animals could be identified by Southern blot and quantitative PCR, showing a strong trend to increased transgenic protein expression. In homozygous animals, atrial hypertrophy appeared earlier and more pronounced than in hemizygous animals, going along with an earlier onset of spontaneous AF, while no increased early mortality was observed. Application of a rate-controlling drug (esmolol) led to the expected result of a decreased heart rate. Application of a rhythm-controlling drug (flecainide) showed effects on heart rate variability, but did not lead to a definitive conversion to sinus rhythm.

Conclusion: We suggest homozygous CREM-IbΔC-X overexpressing mice as a reliable model of early onset, rapidly progressive AF.

Regulation and Function of TMEM16F in Renal Podocytes

The Ca²⁺-activated phospholipid scramblase and ion channel TMEM16F is expressed in podocytes of renal glomeruli. Podocytes are specialized cells that form interdigitating foot processes as an essential component of the glomerular filter. These cells, which participate in generation of the primary urine, are often affected during primary glomerular diseases, such as glomerulonephritis and secondary hypertensive or diabetic nephropathy, which always leads to proteinuria. Because the function of podocytes is known to be controlled by intracellular Ca²⁺ signaling, it is important to know about the role of Ca²⁺-activated TMEM16F in these cells. To that end, we generated an inducible TMEM16F knockdown in the podocyte cell line AB8, and produced a conditional mouse model with knockout of TMEM16F in podocytes and renal epithelial cells of the nephron. We found that knockdown of TMEM16F did not produce proteinuria or any obvious phenotypic changes. Knockdown of TMEM16F affected cell death of tubular epithelial cells but not of glomerular podocytes when analyzed in TUNEL assays. Surprisingly, and in contrast to other cell types, TMEM16F did not control intracellular Ca²⁺ signaling and was not responsible for Ca²⁺-activated whole cell currents in podocytes. TMEM16F levels in podocytes were enhanced after inhibition of the endolysosomal pathway and after treatment with angiotensin II. Renal knockout of TMEM16F did not compromise renal morphology and serum electrolytes. Taken together, in contrast to other cell types, such as platelets, bone cells, and immune cells, TMEM16F shows little effect on basal properties of podocytes and does not appear to be essential for renal function.

Eukaryotic elongation factor 2 is a prognostic marker and its kinase a potential therapeutic target in HCC

Hepatocellular carcinoma is a cancer with increasing incidence and largely refractory to current anticancer drugs. Since Sorafenib, a multikinase inhibitor has shown modest efficacy in advanced hepatocellular carcinoma additional treatments are highly needed. Protein phosphorylation via kinases is an important post-translational modification to regulate cell homeostasis including proliferation and apoptosis. Therefore kinases are valuable targets in cancer therapy. To this end we performed 2D differential gel electrophoresis and mass spectrometry analysis of phosphoprotein-enriched lysates of tumor and corresponding non-tumorous liver samples to detect differentially abundant phosphoproteins to screen for novel kinases as potential drug targets. We identified 34 differentially abundant proteins in phosphoprotein enriched lysates. Expression and distribution of the candidate protein eEF2 and its phosphorylated isoform was validated immunohistochemically on 78 hepatocellular carcinoma and non-tumorous tissue samples. Validation showed that total eEF2 and phosphorylated eEF2 at threonine 56 are prognostic markers for overall survival of HCC-patients. The activity of the regulating eEF2 kinase, compared between tumor and non-tumorous tissue lysates by in vitro kinase assays, is more than four times higher in tumor tissues. Functional analyzes regarding eEF2 kinase were performed in JHH5 cells with CRISPR/Cas9 mediated eEF2 kinase knock out. Proliferation and growth is decreased in eEF2 kinase knock out cells.

Differential effects of anoctamins on intracellular calcium signals

The Ca²⁺-activated Cl^- channel TMEM16A [anoctamin (ANO)1] is homologous to yeast Ist2 and has been shown to tether the cortical endoplasmic reticulum (ER) to the plasma membrane. We therefore examined whether ANO1 and other members of the ANO family affect intracellular Ca²⁺ ([Ca²⁺]_i) signals. It is shown that expression of ANO1 augments Ca²⁺ store release upon stimulation of GPCRs, whereas knockdown of ANO1, or lack of Ano1 expression in Ano1^-/- animals, as shown in an earlier report, inhibits Ca²⁺ release. ANO6, and -10 show similar effects, whereas expression of ANO4, -8, and -9 attenuate filling of the ER store. The impact of ANO1 and -4 were examined in more detail. ANO1 colocalized and interacted with IP₃R, whereas ANO4 colocalized with SERCA Ca²⁺ pumps and interacted with ORAI-1 channels, respectively. ANO1 Cl currents were rapidly activated exclusively through Ca²⁺ store release, and remained untouched by influx of extracellular Ca²⁺ In contrast expression of ANO4 caused a delayed activation of membrane-localized ANO6 channels, solely through store-operated Ca²⁺ entry via ORAI. Ca²⁺ signals were inhibited by knocking down expression of endogenous ANO1, -5, -6, and -10 and were also reduced in epithelial cells from Ano10^-/- mice. The data suggest that ANOs affect compartmentalized [Ca²⁺]_i signals, which may explain some of the cellular defects related to ANO mutations.-Cabrita, I., Benedetto, R., Fonseca, A., Wanitchakool, P., Sirianant, L., Skryabin, B. V., Schenk, L. K., Pavenstädt, H., Schreiber, R., Kunzelmann, K. Differential effects of anoctamins on intracellular calcium signals.

Lmbrd1 expression is essential for the initiation of gastrulation

The rare inborn cblF defect of cobalamin metabolism is caused by mutations in the limb region 1 (LMBR1) domain containing 1 gene (LMBRD1). This defect is characterized by massive accumulation of free cobalamin in lysosomes and loss of mitochondrial succinyl‐CoA synthesis and cytosolic methionine synthesis. Affected children suffer from heart defects, developmental delay and megaloblastic anemia. LMBRD1 encodes for LMBD1, a predicted lysosomal cobalamin transport protein. In this study, we determine the physiological function of LMBRD1 during embryogenesis by generating Lmbrd1 deficient mice using the Cre/LoxP system. Complete loss of Lmbrd1 function is accompanied by early embryonic death in mice. Whole mount in situ hybridization studies against bone morphogenetic protein 4 and Nodal show that initial formation of the proximal–distal axis is unaffected in early embryonic stages whereas the initiation of gastrulation is disturbed shown by the expression pattern of even skipped homeotic gene 1 and fibroblast growth factor 8 in Lmbrd1 deficient mice. We conclude that intact function of LMBD1 is essential for the initiation of gastrulation.

Maternal transcription of non-protein coding RNAs from the PWS-critical region rescues growth retardation in mice

Prader-Willi syndrome (PWS) is a neurogenetic disorder caused by loss of paternally expressed genes on chromosome 15q11-q13. The PWS-critical region (PWScr) contains an array of non-protein coding IPW-A exons hosting intronic SNORD116 snoRNA genes. Deletion of PWScr is associated with PWS in humans and growth retardation in mice exhibiting ~15% postnatal lethality in C57BL/6 background. Here we analysed a knock-in mouse containing a 5'HPRT-LoxP-Neo(R) cassette (5'LoxP) inserted upstream of the PWScr. When the insertion was inherited maternally in a paternal PWScr-deletion mouse model (PWScr(p-/m5'LoxP)), we observed compensation of growth retardation and postnatal lethality. Genomic methylation pattern and expression of protein-coding genes remained unaltered at the PWS-locus of PWScr(p-/m5'LoxP) mice. Interestingly, ubiquitous Snord116 and IPW-A exon transcription from the originally silent maternal chromosome was detected. In situ hybridization indicated that PWScr(p-/m5'LoxP) mice expressed Snord116 in brain areas similar to wild type animals. Our results suggest that the lack of PWScr RNA expression in certain brain areas could be a primary cause of the growth retardation phenotype in mice. We propose that activation of disease-associated genes on imprinted regions could lead to general therapeutic strategies in associated diseases.

Neuronal expression of the human neuropeptide S receptor NPSR1 identifies NPS-induced calcium signaling pathways

The neuropeptide S (NPS) system was discovered as a novel neurotransmitter system a decade ago and has since been identified as a key player in the modulation of fear and anxiety. Genetic variations of the human NPS receptor (NPSR1) have been associated with pathologies like panic disorders. However, details on the molecular fundamentals of NPSR1 activity in neurons remained elusive. We expressed NPSR1 in primary hippocampal cultures. Using single-cell calcium imaging we found that NPSR1 stimulation induced calcium mobilization from the endoplasmic reticulum via activation of IP₃ and ryanodine receptors. Store-operated calcium channels were activated in a downstream process mediating entry of extracellular calcium. We provide the first detailed analysis of NPSR1 activity and the underlying intracellular pathways with respect to calcium mobilization in neurons.

FHL2 regulates the resolution of tissue damage in chronic inflammatory arthritis

Objective

We analysed the role of the adaptor molecule four-and-a-half Lin11, Isl-1 & Mec-3 (LIM) domain protein 2 (FHL2) in the activation of fibroblast-like synoviocytes in human rheumatoid arthritis (RA) and tumour necrosis factor α (TNFα)-dependent animal models of the disease.

Methods

Synovial tissues of patients with RA and osteoarthritis (OA) as well as hind paw sections from arthritic human TNFα transgenic (hTNFtg) mice and synovial fibroblasts from these were analysed. The effects of cytokines on the expression of FHL2 and disease-relevant matrixmetalloproteases (MMPs) were determined. Analyses of human tissue specimens from patients treated with anti-TNFα as well as anti-TNFα treatment of hTNFtg mice were performed to substantiate the TNFα effects on FHL2 levels. FHL2−/− mice and hTNFtg mice (with constitutive or inducible transgene expression) were crossbred to generate TNFα overexpressing FHL2-deficient animals. Signalling pathways were analysed in cells from these mice and in human cells after knock down of FHL2 by western blot.

Results

FHL2 levels were higher in RA than in OA and in hTNFtg than in wild-type mice. Surprisingly, while transforming growth factor (TGF)β-induced FHL2 expression, TNFα suppressed FHL2. In vivo, anti-TNFα treatment led to higher FHL2 levels both in RA patients and hTNFtg mice. The loss of FHL2 increased joint destruction in hTNFtg mice, which was accompanied by elevated MMP-13. In vitro, TNFα-mediated MMP-13 was significantly higher in FHL2−/− cells and after knock down of FHL2, which was caused by prolonged p38 MAPK activation.

Conclusions

These data suggest that FHL2 serves as a protective factor and that, rather than promoting the pathology, the upregulation of FHL2 in RA occurs in frame of a regenerative attempt.

Annexin A8 controls leukocyte recruitment to activated endothelial cells via cell surface delivery of CD63

To enable leukocyte adhesion to activated endothelium, the leukocyte receptor P-selectin is released from Weibel-Palade bodies (WPB) to the endothelial cell surface where it is stabilized by CD63. Here we report that loss of annexin A8 (anxA8) in human umbilical vein endothelial cells (HUVEC) strongly decreases cell surface presentation of CD63 and P-selectin, with a concomitant reduction in leukocyte rolling and adhesion. We confirm the compromised leukocyte adhesiveness in inflammatory-activated endothelial venules of anxA8-deficient mice. We find that WPB of anxA8-deficient HUVEC contain less CD63, and that this is caused by improper transport of CD63 from late multivesicular endosomes to WPB, with CD63 being retained in intraluminal vesicles. Consequently, reduced CD63 cell surface levels are seen following WPB exocytosis, resulting in enhanced P-selectin re-internalization. Our data support a model in which anxA8 affects leukocyte recruitment to activated endothelial cells by supplying WPB with sufficient amounts of the P-selectin regulator CD63.

Doxycycline-induced expression of transgenic human tumor necrosis factor α in adult mice results in psoriasis-like arthritis

Objective

To generate doxycycline-inducible human tumor necrosis factor α (TNFα)–transgenic mice to overcome a major disadvantage of existing transgenic mice with constitutive expression of TNFα, which is the limitation in crossing them with various knockout or transgenic mice.

Methods

A transgenic mouse line that expresses the human TNFα cytokine exclusively after doxycycline administration was generated and analyzed for the onset of diseases.

Results

Doxycycline-inducible human TNFα–transgenic mice developed an inflammatory arthritis– and psoriasis-like phenotype, with fore and hind paws being prominently affected. The formation of “sausage digits” with characteristic involvement of the distal interphalangeal joints and nail malformation was observed. Synovial hyperplasia, enthesitis, cartilage and bone alterations, formation of pannus tissue, and inflammation of the skin epidermis and nail matrix appeared as early as 1 week after the treatment of mice with doxycycline and became aggravated over time. The abrogation of human TNFα expression by the removal of doxycycline 6 weeks after beginning stimulation resulted in fast resolution of the most advanced macroscopic and histologic disorders, and 3–6 weeks later, only minimal signs of disease were visible.

Conclusion

Upon doxycycline administration, the doxycycline-inducible human TNFα–transgenic mouse displays the major features of inflammatory arthritis. It represents a unique animal model for studying the molecular mechanisms of arthritis, especially the early phases of disease genesis and tissue remodeling steps upon abrogation of TNFα expression. Furthermore, unlimited crossing of doxycycline-inducible human TNFα–transgenic mice with various knockout or transgenic mice opens new possibilities for unraveling the role of various signaling molecules acting in concert with TNFα.

A modified TALEN-based system for robust generation of knock-out human pluripotent stem cell lines and disease models

BACKGROUND

Transcription activator-like effector nucleases (TALENs) have emerged as a tool for enabling targeted gene editing and disruption in difficult systems, such as human pluripotent stem cells (hPSCs). The modular architecture of TAL effectors theoretically enables targeting of any genomic locus and several cloning systems for custom TALEN assembly have recently been established. However, there is a lack of versatile TALEN expression systems applicable to hPSCs.

RESULTS

Here, we extend an existing TALE assembly system by a dual set of expression vectors for efficient application of TALEN technology in hPSCs. This is characterized by improved TALEN architecture as well as antibiotic resistance and fluorescent reporter cassettes, thus enabling enrichment for transfected cells. Improved functionality of the combined system was demonstrated by targeted disruption of the HPRT1 gene to create isogenic disease models of Lesch-Nyhan-Syndrome. Using female hPSCs, homozygous disruption of HPRT1 occurred at efficiencies of up to 15%. Differentiating isogenic knock-out cells both into central nervous system (CNS) as well as into sensory-like neurons recapitulated previously described phenotypes based on patient-specific induced PSCs and extended these findings to non-CNS neurons, respectively.

CONCLUSION

The combined vector system allows for flexible and affordable generation of knock-out hPSCs lines, thus enabling investigation of developmental processes as well as the generation of isogenic disease models without the need for patient material.

KIBRA (KIdney/BRAin protein) regulates learning and memory and stabilizes Protein kinase Mζ

The WWC1 gene has been genetically associated with human episodic memory performance, and its product KIdney/BRAin protein (KIBRA) has been shown to interact with the atypical protein kinase protein kinase M ζ (PKMζ). Although recently challenged, PKMζ remains a candidate postsynaptic regulator of memory maintenance. Here, we show that PKMζ is subject to rapid proteasomal degradation and that KIBRA is both necessary and sufficient to counteract this process, thus stabilizing the kinase and maintaining its function for a prolonged time. We define the binding sequence on KIBRA, a short amino acid motif near the C-terminus. Both hippocampal knock-down of KIBRA in rats and KIBRA knock-out in mice result in decreased learning and memory performance in spatial memory tasks supporting the notion that KIBRA is a player in episodic memory. Interestingly, decreased memory performance is accompanied by decreased PKMζ protein levels. We speculate that the stabilization of synaptic PKMζ protein levels by KIBRA may be one mechanism by which KIBRA acts in memory maintenance. KIBRA/WWC1 has been genetically associated with human episodic memory. KIBRA has been shown to be post-synaptically localized, but its function remained obscure. Here, we show that KIBRA shields PKMζ, a kinase previously linked to memory maintenance, from proteasomal degradation via direct interaction. KIBRA levels in the rodent hippocampus correlate closely both to spatial memory performance in rodents and to PKMζ levels. Our findings support a role for KIBRA in memory, and unveil a novel function for this protein.

Autistic-like behaviours and hyperactivity in mice lacking ProSAP1/Shank2

Autism spectrum disorders comprise a range of neurodevelopmental disorders characterized by deficits in social interaction and communication, and by repetitive behaviour. Mutations in synaptic proteins such as neuroligins, neurexins, GKAPs/SAPAPs and ProSAPs/Shanks were identified in patients with autism spectrum disorder, but the causative mechanisms remain largely unknown. ProSAPs/Shanks build large homo- and heteromeric protein complexes at excitatory synapses and organize the complex protein machinery of the postsynaptic density in a laminar fashion. Here we demonstrate that genetic deletion of ProSAP1/Shank2 results in an early, brain-region-specific upregulation of ionotropic glutamate receptors at the synapse and increased levels of ProSAP2/Shank3. Moreover, ProSAP1/Shank2(-/-) mutants exhibit fewer dendritic spines and show reduced basal synaptic transmission, a reduced frequency of miniature excitatory postsynaptic currents and enhanced N-methyl-d-aspartate receptor-mediated excitatory currents at the physiological level. Mutants are extremely hyperactive and display profound autistic-like behavioural alterations including repetitive grooming as well as abnormalities in vocal and social behaviours. By comparing the data on ProSAP1/Shank2(-/-) mutants with ProSAP2/Shank3αβ(-/-) mice, we show that different abnormalities in synaptic glutamate receptor expression can cause alterations in social interactions and communication. Accordingly, we propose that appropriate therapies for autism spectrum disorders are to be carefully matched to the underlying synaptopathic phenotype.

Inhibitor of cyclin-dependent kinase (CDK) interacting with cyclin A1 (INCA1) regulates proliferation and is repressed by oncogenic signaling

The cell cycle is driven by the kinase activity of cyclin·cyclin-dependent kinase (CDK) complexes, which is negatively regulated by CDK inhibitor proteins. Recently, we identified INCA1 as an interaction partner and a substrate of cyclin A1 in complex with CDK2. On a functional level, we identified a novel cyclin-binding site in the INCA1 protein. INCA1 inhibited CDK2 activity and cell proliferation. The inhibitory effects depended on the cyclin-interacting domain. Mitogenic and oncogenic signals suppressed INCA1 expression, whereas it was induced by cell cycle arrest. We established a deletional mouse model that showed increased CDK2 activity in spleen with altered spleen architecture in Inca1(-/-) mice. Inca1(-/-) embryonic fibroblasts showed an increase in the fraction of S-phase cells. Furthermore, blasts from acute lymphoid leukemia and acute myeloid leukemia patients expressed significantly reduced INCA1 levels highlighting its relevance for growth control in vivo. Taken together, this study identifies a novel CDK inhibitor with reduced expression in acute myeloid and lymphoid leukemia. The molecular events that control the cell cycle occur in a sequential process to ensure a tight regulation, which is important for the survival of a cell and includes the detection and repair of genetic damage and the prevention of uncontrolled cell division.

A global view of the nonprotein-coding transcriptome in Plasmodium falciparum

Nonprotein-coding RNAs (npcRNAs) represent an important class of regulatory molecules that act in many cellular pathways. Here, we describe the experimental identification and validation of the small npcRNA transcriptome of the human malaria parasite Plasmodium falciparum. We identified 630 novel npcRNA candidates. Based on sequence and structural motifs, 43 of them belong to the C/D and H/ACA-box subclasses of small nucleolar RNAs (snoRNAs) and small Cajal body-specific RNAs (scaRNAs). We further observed the exonization of a functional H/ACA snoRNA gene, which might contribute to the regulation of ribosomal protein L7a gene expression. Some of the small npcRNA candidates are from telomeric and subtelomeric repetitive regions, suggesting their potential involvement in maintaining telomeric integrity and subtelomeric gene silencing. We also detected 328 cis-encoded antisense npcRNAs (asRNAs) complementary to P. falciparum protein-coding genes of a wide range of biochemical pathways, including determinants of virulence and pathology. All cis-encoded asRNA genes tested exhibit lifecycle-specific expression profiles. For all but one of the respective sense–antisense pairs, we deduced concordant patterns of expression. Our findings have important implications for a better understanding of gene regulatory mechanisms in P. falciparum, revealing an extended and sophisticated npcRNA network that may control the expression of housekeeping genes and virulence factors.

Alternative splicing of the guanylyl cyclase-A receptor modulates atrial natriuretic peptide signaling

Atrial (ANP) and B-type natriuretic peptides (BNP) modulate blood pressure and volume through the stimulation of cyclic GMP production by their guanylyl cyclase-A (GC-A) receptor. A novel isoform of GC-A has been identified that is the result of differential splicing of exon 4. The deletion of a 51-bp sequence is predicted to delete 17 amino acids (Lys314-Gln330) in the membrane-distal part of the extracellular domain. Reverse transcription-PCR analyses demonstrated low messenger RNA expression levels of spliced GC-A in all tissues. Homology modeling suggested that the alterations in the protein structure could interfere with ANP binding or signaling. Indeed, functional studies in transfected HEK 293 cells demonstrated that binding of ANP and ANP-induced cyclic GMP formation by GC-ADelta(Lys314-Gln330) were totally abolished. Furthermore, cotransfection studies showed that this GC-A variant forms heterodimers with the wild type receptor and inhibits ligand-inducible cGMP generation. Finally, treatment of mice with angiotensin II (300 ng/kg/min during 7 days) resulted in enhanced pulmonary mRNA expression of spliced GC-A, which was concomitant to diminished GC-A/cGMP responses to ANP. We conclude that alternative splicing can regulate endogenous ANP/GC-A signaling. Angiotensin II-induced alternative splicing of GC-A may represent a novel mechanism for reducing the sensitivity to ANP.

Deletion of the MBII-85 snoRNA gene cluster in mice results in postnatal growth retardation

Prader-Willi syndrome (PWS [MIM 176270]) is a neurogenetic disorder characterized by decreased fetal activity, muscular hypotonia, failure to thrive, short stature, obesity, mental retardation, and hypogonadotropic hypogonadism. It is caused by the loss of function of one or more imprinted, paternally expressed genes on the proximal long arm of chromosome 15. Several potential PWS mouse models involving the orthologous region on chromosome 7C exist. Based on the analysis of deletions in the mouse and gene expression in PWS patients with chromosomal translocations, a critical region (PWScr) for neonatal lethality, failure to thrive, and growth retardation was narrowed to the locus containing a cluster of neuronally expressed MBII-85 small nucleolar RNA (snoRNA) genes. Here, we report the deletion of PWScr. Mice carrying the maternally inherited allele (PWScr(m-/p+)) are indistinguishable from wild-type littermates. All those with the paternally inherited allele (PWScr(m+/p-)) consistently display postnatal growth retardation, with about 15% postnatal lethality in C57BL/6, but not FVB/N crosses. This is the first example in a multicellular organism of genetic deletion of a C/D box snoRNA gene resulting in a pronounced phenotype.

Can ID repetitive elements serve as cis-acting dendritic targeting elements? An in vivo study

Dendritic localization of mRNA/RNA involves interaction of cis-elements and trans-factors. Small, non-protein coding dendritic BC1 RNA is thought to regulate translation in dendritic microdomains. Following microinjections into cultured cells, BC1 RNA fused to larger mRNAs appeared to impart transport competence to these chimeras, and its 5' ID region was proposed as the cis-acting dendritic targeting element. As these ID elements move around rodent genomes and, if transcribed, form a long RNA stem-loop, they might, thereby, lead to new localizations for targeted gene products. To test their targeting ability in vivo we created transgenic mice expressing various ID elements fused to the 3' UTR of reporter mRNA for Enhanced Green Fluorescent Protein. In vivo, neither ID elements nor the BC1 RNA coding region were capable of transporting EGFP RNA to dendrites, although the 3' UTR of alpha-CaMKII mRNA, an established cis-acting element did produce positive results. Other mRNAs containing naturally inserted ID elements are also not found in neuronal dendrites. We conclude that the 5' ID domain from BC1 RNA is not a sufficient dendritic targeting element for mRNAs in vivo.

Two primate-specific small non-protein-coding RNAs in transgenic mice: neuronal expression, subcellular localization and binding partners

In a rare occasion a single chromosomal locus was targeted twice by independent Alu-related retroposon insertions, and in both cases supported neuronal expression of the respective inserted genes encoding small non-protein coding RNAs (npcRNAs): BC200 RNA in anthropoid primates and G22 RNA in the Lorisoidea branch of prosimians. To avoid primate experimentation, we generated transgenic mice to study neuronal expression and protein binding partners for BC200 and G22 npcRNAs. The BC200 gene, with sufficient upstream flanking sequences, is expressed in transgenic mouse brain areas comparable to those in human brain, and G22 gene, with upstream flanks, has a similar expression pattern. However, when all upstream regions of the G22 gene were removed, expression was completely abolished, despite the presence of intact internal RNA polymerase III promoter elements. Transgenic BC200 RNA is transported into neuronal dendrites as it is in human brain. G22 RNA, almost twice as large as BC200 RNA, has a similar subcellular localization. Both transgenically expressed npcRNAs formed RNP complexes with poly(A) binding protein and the heterodimer SRP9/14, as does BC200 RNA in human. These observations strongly support the possibility that the independently exapted npcRNAs have similar functions, perhaps in translational regulation of dendritic protein biosynthesis in neurons of the respective primates.

Vascular endothelium is critically involved in the hypotensive and hypovolemic actions of atrial natriuretic peptide

Atrial natriuretic peptide (ANP), via its vasodilating and diuretic effects, has an important physiological role in the maintenance of arterial blood pressure and volume. Its guanylyl cyclase-A (GC-A) receptor is highly expressed in vascular endothelium, but the functional relevance of this is controversial. To dissect the endothelium-mediated actions of ANP in vivo, we inactivated the GC-A gene selectively in endothelial cells by homologous loxP/Tie2-Cre-mediated recombination. Notably, despite full preservation of the direct vasodilating effects of ANP, mice with endothelium-restricted deletion of the GC-A gene (EC GC-A KO) exhibited significant arterial hypertension and cardiac hypertrophy. Echocardiographic and Doppler flow evaluations together with the Evan's blue dilution technique showed that the total plasma volume of EC GC-A KO mice was increased by 11-13%, even under conditions of normal dietary salt intake. Infusion of ANP caused immediate increases in hematocrit in control but not in EC GC-A KO mice, which indicated that ablation of endothelial GC-A completely prevented the acute contraction of intravascular volume produced by ANP. Furthermore, intravenous ANP acutely enhanced the rate of clearance of radio-iodinated albumin from the circulatory system in control but not in EC GC-A KO mice. We conclude that GC-A-mediated increases in endothelial permeability are critically involved in the hypovolemic, hypotensive actions of ANP.

Hypervolemic hypertension in mice with systemic inactivation of the (floxed) guanylyl cyclase-A gene by alphaMHC-Cre-mediated recombination

To dissect the tissue-specific functions of atrial natriuretic peptide (ANP), we recently introduced loxP sites into the murine gene for its receptor, guanylyl cyclase-A (GC-A), by homologous recombination (tri-lox GC-A). For either smooth-muscle or cardiomyocyte-restricted deletion of GC-A, floxed GC-A mice were mated to transgenic mice expressing Cre-recombinase under the control of the smooth-muscle SM22 or the cardiac alphaMHC promoter. As shown in these studies, Cre-mediated recombination of the floxed GC-A gene fully inactivated GC-A function in a cell-restricted manner. In the present study we show that alphaMHC-Cre, but not SM22-Cre, with high frequency generates genomic recombinations of the floxed GC-A gene segments which were transmitted to the germline. Alleles with partial or complete deletions were readily recovered from the next generation, after segregation of the Cre-transgene. We took advantage of this strategy to generate a new mouse line with global, systemic deletion of GC-A. Doppler-echocardiographic and physiological studies in these mice demonstrate for the first time the tremendous impact of ANP/GC-A dysfunction on chronic blood volume homeostasis.

Role of a neuronal small non-messenger RNA: behavioural alterations in BC1 RNA-deleted mice

BC1 RNA is a small non-messenger RNA common in dendritic microdomains of neurons in rodents. In order to investigate its possible role in learning and behaviour, we compared controls and knockout mice from three independent founder lines established from separate embryonic stem cells. Mutant mice were healthy with normal brain morphology and appeared to have no neurological deficits. A series of tests for exploration and spatial memory was carried out in three different laboratories. The tests were chosen as to ensure that different aspects of spatial memory and exploration could be separated and that possible effects of confounding variables could be minimised. Exploration was studied in a barrier test, in an open-field test, and in an elevated plus-maze test. Spatial memory was investigated in a Barnes maze and in a Morris water maze (memory for a single location), in a multiple T-maze and in a complex alley maze (route learning), and in a radial maze (working memory). In addition to these laboratory tasks, exploratory behaviour and spatial memory were assessed under semi-naturalistic conditions in a large outdoor pen. The combined results indicate that BC1 RNA-deficient animals show behavioural changes best interpreted in terms of reduced exploration and increased anxiety. In contrast, spatial memory was not affected. In the outdoor pen, the survival rates of BC1-depleted mice were lower than in controls. Thus, we conclude that the neuron-specific non-messenger BC1 RNA contributes to the aptive modulation of behaviour.

Enhanced contact hypersensitivity and antiviral immune responsesin vivo by keratinocyte-targeted overexpression of IL-15

IL-15 is involved in lymphocyte homeostasis. To investigate the role of IL-15 in the skin in vivo, mice were generated that overexpress IL-15 in keratinocytes, resulting in increased IL-15 protein levels in the skin but not elevated IL-15 serum concentrations. Keratin 14 (K14)-IL-15 transgenic (tg) mice showed increased contact hypersensitivity (CHS) responses. Transfer of primed wild-type (wt) and tg T cells into naive wt or tg recipients indicated that skin-derived IL-15 enhanced the induction but not the elicitation phase of CHS. Tg mice could be sensitized even by suboptimal hapten concentrations. Accordingly, Langerhans cells (LC) from tg skin were identified as potent allostimulators, suggesting the involvement of IL-15-stimulated LC in the induction of adaptive immunity. Overexpression of IL-15 also strengthened innate immunity since tg mice infected with human HSV type I developed significantly smaller HSV skin lesions. In addition, tg mice resisted re-infection with HSV more effectively than wt mice did, which was associated with an elevated anti-HSV Ab production. Accordingly, injection of serum from re-infected tg mice protected naive recipients significantly from epicutaneous HSV infection, indicating that anti-HSV Ab produced by tg mice play an important role in resistance in vivo. Together, our results show that overexpression of IL-15 in the epidermis enhances both innate and adaptive cutaneous immunity.