Abstract 10: Hyeprtension

Aldosterone is a critical driver for cardiovascular disease (CVD). We recently discovered that MANP, a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP. MANP is currently entering clinical trials for hypertension and thus understanding its aldosterone suppressing mechanism is important. The mechanism of aldosterone inhibition by natriuretic peptides (NPs) remains to be clearly defined. Conflicting results were reported on the roles of particulate guanylyl cyclase A receptor (pGC-A) and NP clearance receptor (NPRC) in aldosterone inhibition. Furthermore, the functions of protein kinase G (PKG) and phosphodiesterases (PDE) on aldosterone regulation are not clear. Herein, we investigated the molecular mechanism of aldosterone regulation in the human adrenocortical cell line H295R and in mice. We firstly showed that pGC-A mediates aldosterone inhibition. In contrast, with NPRC agonist and antagonist, we showed that NPRC did not inhibit aldosterone. Next, we confirmed that MANP inhibits aldosterone via PDE2, not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer (FRET) experiments. Specifically, MANP suppressed ANGII mediated activation of aldosterone (fold change) MANP+ANGII 3.2±0.1* vs. ANGII 3.8±0.1 (*p<0.05) with IBMX, a PDEs inhibitor and the PDE2 antagonist Bay 60-7550 reversed MANP-mediated aldosterone suppression (IBMX+MANP+ANGII 3.9±0.2 and Bay+MANP+ANGII 4.1±0.1). With PKG agonists and inhibitors, aldosterone levels were not changed. In PDE2 activity FRET studies, aldosterone control was 3.7±0.4 and with MANP 0.9±0.2* supporting PDE2 activation by MANP. Further, the inhibitory effect of PDE2 is mediated by a reduction of intracellular Ca2+ concentration (~22%). We then showed that MANP directly reduced aldosterone synthase CYP11B2 expression in vitro. Lastly, in PDE2 knockout mice (embryonic lethal), embryonic adrenal CYP11B2 expression is markedly increased (wild type: 1±0.2, KO: 2.8±0.5*). Our findings innovatively elucidate the pGC-A/cGMP/PDE2 pathway in aldosterone inhibition by MANP in vitro and in vivo. Additionally, our data also support the development of MANP as a novel ANP analog drug for CVD.

Natriuretic Peptide Clearance Receptor (NPR-C) Pathway as a Novel Therapeutic Target in Obesity-Related Heart Failure With Preserved Ejection Fraction (HFpEF)

Heart failure (HF) with preserved ejection fraction (HFpEF) is a major public health problem with cases projected to double over the next two decades. There are currently no US Food and Drug Administration–approved therapies for the health-related outcomes of HFpEF. However, considering the high prevalence of this heterogeneous syndrome, a directed therapy for HFpEF is one the greatest unmet needs in cardiovascular medicine. Additionally, there is currently a lack of mechanistic understanding about the pathobiology of HFpEF. The phenotyping of HFpEF patients into pathobiological homogenous groups may not only be the first step in understanding the molecular mechanism but may also enable the development of novel targeted therapies. As obesity is one of the most common comorbidities found in HFpEF patients and is associated with many cardiovascular effects, it is a viable candidate for phenotyping. Large outcome trials and registries reveal that being obese is one of the strongest independent risk factors for developing HFpEF and that this excess risk may not be explained by traditional cardiovascular risk factors. Recently, there has been increased interest in the intertissue communication between adipose tissue and the heart. Evidence suggests that the natriuretic peptide clearance receptor (NPR-C) pathway may play a role in the development and pathobiology of obesity-related HFpEF. Therefore, therapeutic manipulations of the NPR-C pathway may represent a new pharmacological strategy in the context of underlying molecular mechanisms.

Anti-sortilin1 Antibody Up-Regulates Progranulin via Sortilin1 Down-Regulation

Progranulin (PGRN) haploinsufficiency associated with loss-of-function mutations in the granulin gene causes frontotemporal dementia (FTD). This suggests that increasing PGRN levels could have promising therapeutic implications for patients carrying GRN mutations. In this study, we explored the therapeutic potential of sortilin1 (SORT1), a clearance receptor of PGRN, by generating and characterizing monoclonal antibodies against SORT1. Anti-SORT1 monoclonal antibodies were generated by immunizing Sort1 knockout mice with SORT1 protein. The antibodies were classified into 7 epitope bins based on their competitive binding to the SORT1 protein and further defined by epitope bin-dependent characteristics, including SORT1-PGRN blocking, SORT1 down-regulation, and binding to human and mouse SORT1. We identified a positive correlation between PGRN up-regulation and SORT1 down-regulation. Furthermore, we also characterized K1-67 antibody via SORT1 down-regulation and binding to mouse SORT1 in vivo and confirmed that K1-67 significantly up-regulated PGRN levels in plasma and brain interstitial fluid of mice. These data indicate that SORT1 down-regulation is a key mechanism in increasing PGRN levels via anti-SORT1 antibodies and suggest that SORT1 is a potential target to correct PGRN reduction, such as that in patients with FTD caused by GRN mutation.

Role of the Hyaluronan Receptor, Stabilin-2/HARE, in Health and Disease

Stabilin-2/HARE is the primary clearance receptor for circulating hyaluronan (HA), a polysaccharide found in the extracellular matrix (ECM) of metazoans. HA has many biological functions including joint lubrication, ocular turgor pressure, skin elasticity and hydration, cell motility, and intercellular signaling, among many others. The regulatory system for HA content in the tissues, lymphatics, and circulatory systems is due, in part, to Stabilin-2/HARE. The activity of this receptor was discovered about 40 years ago (early 1980s), cloned in the mid-1990s, and has been characterized since then. Here, we discuss the overall domain organization of this receptor and how it correlates to ligand binding, cellular signaling, and its role in known physiological disorders such as cancer.

Current Updates on the Regulation of Beta-Secretase Movement as a Potential Restorative Focus for Management of Alzheimer's Disease

The most recent decade was described by a developing awareness about the seriousness of dementia in the field of age-related people. Among the dementias, Alzheimer&#039;s assumes a plentiful role as a result of its amazingly high rate and casualty. A few pharmacological procedures have been attempted yet at the same time now, Alzheimer continues being an untreatable malady. The collection of A&#946; in the brain is an early poisonous occasion in the pathogenesis of Alzheimer&#039;s disease, which is the most widely recognized type of dementia correlated with plaques and tangles within the brain. However, the mechanism of the intraneuronal direction of BACE1 is poorly understood. AD is caused by mutations in one of the genes that encoding APP, presenilins 1 and 2. Most of the mutations in these genes increase A&#946;42 production. Numerous receptors are associated with initiating A&#946; transport and clearance. Among them, RAGE is an influx transport receptor that binds soluble A&#946; and mediates pathophysiological cellular responses. RAGE additionally intervenes the vehicle of plasma A&#946; over the blood-brain barrier. LRP-1 functions as a clearance receptor for A&#946; at the blood-brain barrier. The regulation of beta-secretase movement is being explored as a potential restorative focus for treating AD.

Discovery of the Liver Hyaluronan Receptor for Endocytosis (HARE) and Its Progressive Emergence as the Multi-Ligand Scavenger Receptor Stabilin-2

Since the discovery of a novel liver hyaluronan (HA) clearance receptor in 1981 by Laurent, Fraser and coworkers, 22 different ligands cleared by the renamed receptor (the Hyaluronan Receptor for Endocytosis (HARE); Stabilin-2 (Stab2)) were discovered over 37 years. Ligands fall into three groups: (1) 11 anionic polymers, (2) seven cleaved or modified proteins and (3) four types of cells. Seven synthetic ligands, not found normally in serum or tissues, likely mimic natural molecules cleared by the receptor. In 2002 we purified and cloned HARE, based on HA-binding activity, and two other groups cloned full-length receptor; FEEL-2 and Stab2. Macrophages likely require full-length Stab2 for efficient binding and phagocytosis of bacteria or apoptotic cells, since cell-binding domains are throughout the receptor. In contrast, all 16 known single-molecule binding sites are only within the C-terminal half (190HARE). The HARE isoform is generated by proteolysis, not mRNA splicing. The majority of circulating ligands is cleared by HARE, since sinusoidal endothelial cells of liver, spleen and lymph node express twice as many HARE half-receptors as full-length receptors. Based on their significant binding and functional differences, a modified receptor nomenclature is proposed that designates HARE as the C-terminal half-receptor isoform and Stab2 as the full-length receptor isoform.

Site-Directed Pegylation at Specific Sites Significantly Prolongs the Half-Life of A1A2A3-VWF By Markedly Attenuating LRP1-Mediated Clearance

Introduction Deficiencies of both von Willebrand Factor (VWF) and FVIII are associated with significant bleeding phenotypes. Consequently, patients with VWD or hemophilia A commonly require replacement therapy with coagulation factor concentrates. However, as infused VWF and FVIII have relatively short plasma half-lives, patient therapy generally necessitates frequent re-dosing. Development of a long-acting rVWF therapy thus represents an important unmet clinical need. We and others have previously demonstrated that the A1A2A3 domains of VWF play a critical role in regulating macrophage-mediated clearance of VWF in vivo. Importantly, crystal structures of the A-domains have also well characterized. In this study, we sought to utilize this data to investigate the hypothesis that site-specific PEGylation within the A1A2A3 domains could be used as a novel strategy to inhibit macrophage-mediated clearance, and thereby inform development of a rVWF molecule with extended plasma half-life. Methodology Site-directed mutagenesis was used to engineer novel surface cysteine residues at selected sites within A1A2A3-VWF. Following purification and characterization, individual A1A2A3 cysteine variants were PEGylated using 40kDa PEG maleimide. Clearance of unPEGylated and PEGylated A1A2A3 variants were assessed in VWF-/- mice. VWF-macrophage interactions were quantified in vitro using differentiated THP-1 macrophages. VWF binding to LRP1 clearance receptor was assessed using both immunosorbant assays and Surface Plasmon Resonance. Results Novel single cysteine residues were introduced at stringently selected sites within A1A2A3-VWF. These sites spanned all 3 A-domains and included; S1286C, Q1353C, M1545C, L1591C, V1636C, Q1652C, V1803C and S1807C. Interestingly, the introduction of these novel cysteine residues in both the A1 and A3 domains of VWF did not alter the rate of VWF clearance compared to WT A1A2A3-VWF. Conversely however, the A2 domain was less tolerant for the insertion of cysteines, with L1591C and V1636C variants demonstrating a significantly reduced VWF plasma half-life of approx. 1.5 fold versus WT-A1A2A3 (p<0.05). Subsequently, the engineered cysteine residues were modified by covalent attachment of a 40kDa branched PEG molecule. All variants achieved greater than 80% PEG conjugation efficiency, except V1636C which was eliminated from further study. Remarkably, PEG conjugation displayed site-specific effects on the in vivo half-life of A1A2A3-VWF. For example, PEGylation at S1286C within the A1 domain resulted in a marked increased in VWF half-life compared to WT-A1A2A3 VWF (92.4±6 vs 18.3±0.9 mins, respectively, p<0.001). Conversely, PEGylation at the adjacent site in the A1 domain, Q1353C, or downstream at M1545C within A2 had no significant effect on VWF half-life (23.3±1 and 20.8±3 mins, respectively). Interestingly, despite the fact that no previous roles have been described for the A3 domain of VWF in regulating its clearance, we observed a significant extension in VWF half-life for PEGylated variants within the A3 domain, V1803C and S1807C, (93.3±9 mins and 58.0±5 mins, respectively, p<0.05). Macrophage LDL receptor related protein 1 (LRP1) has been implicated as key cellular mediator of VWF clearance in vivo. Interestingly, in keeping with the reduced clearance observed for PEGylated VWF variants S1286C, V1803C and S1807C, binding of these variants to clearance receptor LRP1 cluster II and IV was ablated. Conversely, PEGylated variants which failed to extend VWF half-life (Q1353C and M1545C) displayed LRP1 binding that was comparable to WT-A1A2A3 VWF. Interestingly, PEGylation at specific sites in A2 (L1591C and Q1652C) which served to increased VWF half-life displayed normal binding to LRP1 cluster IV. However, binding of these variants to LRP1 cluster II was reduced by 90% compared to WT-A1A2A3. Conclusion Collectively, our novel data demonstrate that cysteine-directed PEGylation at specific sites within the A1 (S1286C), A2 (L1591C, Q1652C) and A3 (V1803C and S1807C) domains of A1A2A3-VWF inhibits binding to macrophage clearance receptor LRP1 in vitro. Consequently, these PEGylated A1A2A3-VWF variants demonstrate an extended circulatory half-life in vivo compared to wild type A1A2A3-VWF. Taken together, these results support the use of site-specific PEGylation as a potential approach to develop long-acting full length rVWF molecules. Disclosures Cooke: Pfizer: Employment. Terraube:Pfizer: Employment. Cohen:Pfizer: Employment. Pittman:Pfizer: Employment. Cunningham:Pfizer: Employment. Lambert:Pfizer: Employment. O'Donnell:Pfizer: Consultancy, Research Funding; Daiichi Sankyo: Consultancy; CSL Behring: Consultancy; Octapharma: Speakers Bureau; Leo Pharma: Speakers Bureau; Novo Nordisk: Research Funding, Speakers Bureau; Bayer: Research Funding, Speakers Bureau; Baxter: Research Funding, Speakers Bureau; Shire: Research Funding, Speakers Bureau.