Nina Wettschureck

Orphan GPCRs of the GPRC5 family regulate macrophage activity and vascular contractility by dimerizing with other GPCRs, but pharmacological modulation of this process has not been explored. We previously identified the dimerization interface of receptor GPRC5B and show here that both its mutation and inhibition by a decoy peptide disturbed the interaction with the prostaglandin E2 receptor EP2 in macrophages, resulting in reduced EP2 signaling, enhanced migration and phagocytosis, and protection from bacterial peritonitis in mice. Furthermore, we show that a similar interface exists in related receptor GPRC5C, and, the same as in GPRC5B, mutation or inhibition by decoy peptide improved host defense. Through a virtual docking screen, we identified a small molecule inhibitor of both GPRC5B and GPRC5C dimerization, K303MP20, and showed that it reduced EP2 signaling, enhanced macrophage activity, and improved host defense in bacterial peritonitis and influenza A infection. Interestingly, K303MP20 not only blocked dimerization between GPRC5B/C and EP2, but also with prostacyclin receptor IP and angiotensin II receptor AT1, resulting in reduced AT1-dependent contraction and enhanced IP-dependent relaxation in human and murine smooth muscle cells. In vivo, K303MP20 did not affect basal blood pressure, but protected mice from angiotensin II–induced hypertension. Taken together, inhibition of orphan GPCR dimerization by small molecules is feasible and improves infection control and arterial hypertension. Pharmacological blockade of GPRC5B/GPRC5C dimerization improves infection control and prevents arterial hypertension.

Peptide-activated G protein-coupled receptors (GPCRs) play crucial roles in numerous diseases, but remain difficult therapeutic targets due to the challenges in developing small-molecule drugs. Here, we explore structure-based strategies to identify small-molecule agonists of neurotensin (NTS) receptors, which hold promise for developing non-opioid analgesics. Chemical libraries of drug-like molecules are first designed based on a receptor-peptide complex, and then 14.5 million compounds are computationally docked to the orthosteric binding site of the NTS ₁ receptor. A set of 39 top-ranked compounds is synthesized, and seven of these are experimentally confirmed to activate the NTS ₁ receptor. Structure-guided optimization yields NTS ₁ ligands with signaling signatures distinct from the endogenous peptide, and these compounds also exhibit high affinity for the NTS ₂ receptor. High-resolution crystal structures of two agonists bound to the NTS ₁ receptor confirm predicted binding modes and reveal key determinants of activation. In vivo, the compounds produce robust antinociception in rodents without inducing hypotension, consistent with a contribution of NTS ₂ receptor activity. To facilitate broader application of our virtual screening approach to peptide-binding GPCRs, we provide access to tailored chemical libraries containing billions of readily synthesizable compounds.

The neuropeptide neurotensin (NTS) is up-regulated in cardiac lymphatic endothelial cells (LECs) in response to ischemic or mechanical damage, but its role in cardiac remodeling is unknown. Here, we aimed to define the role of LEC-derived NTS in cardiac injury responses and to assess the therapeutic potential of targeting cardiac NTS signaling. In cultured murine and human cells, NTS reduced cardiomyocyte hypertrophy and fibroblast activation, and these effects were mediated by NTS receptor 2 (NTSR2)–dependent guanosine 3′,5′-monophosphate (cGMP) production. Consistent with an antihypertrophic and antifibrotic role of NTS, mice with LEC-specific Nts deletion exhibited aggravated hypertrophy and fibrosis after transverse aortic constriction (TAC) and myocardial infarction (MI). Similarly, cardiomyocyte-specific or activated fibroblast-specific inactivation of Ntsr2 led to enhanced cardiac remodeling after TAC. NTSR2 agonist NT150 reproduced the beneficial effects of NTS in cultured human and murine cells and ameliorated cardiac remodeling and dysfunction in both TAC and MI. Additionally, in freshly isolated cardiac tissues from patients with heart failure, NT150 induced cGMP production and suppressed prohypertrophic signaling. These findings identify NTS as an endogenous inhibitor of adverse cardiac remodeling and suggest NTSR2 agonism as a therapeutic strategy in heart failure.

Amyloid precursor protein (APP) gives rise to amyloid-β, a pathological factor in Alzheimer’s disease. However, the physiological role of APP and its homolog amyloid precursor–like protein 2 (APLP2), which are also widely expressed outside the nervous system, is largely unknown. Here, we show that endothelial APP and APLP2 are required for postischemia angiogenesis after myocardial infarction (MI). We found that hypoxia induced the endothelial expression of α-secretases, resulting in nonamyloidogenic processing of APP and APLP2 into the soluble forms APPsα and APLP2sα. Loss of endothelial APP and APLP2 led to decreased neovascularization as well as increased heart failure and mortality after MI, a phenotype that could be rescued by endothelial expression of APPsα. APPsα and APLP2sα exerted their proangiogenic effect by positive allosteric modulation of the endothelial receptor tyrosine kinase KIT, which promotes postischemia neovascularization. Our data identify a function of APP and APLP2 in endothelial cells, which is required for postischemia tissue repair, and suggest approaches to improve regeneration after MI and other ischemic diseases.

In vitro studies have implicated orphan receptor GPRC5B in β cell survival, proliferation, and insulin secretion, but its relevance for glucose homeostasis in vivo is largely unknown. Using tamoxifen-inducible, β cell–specific GPRC5B-KO mice (Ins-G5b–KOs), we show here that loss of GPRC5B does not affect β cell function in the lean state but results in strongly reduced insulin secretion and disturbed glucose tolerance in mice subjected to high-fat diet for 16 weeks. Flow cytometry and single-cell expression analyses in islets from obese mice show a reduced β cell abundance and a less mature β cell phenotype in Ins-G5b–KOs. Expression of β cell–specific transcription factor MafA is reduced both on the RNA and protein level, as are transcripts of MafA target genes. Mechanistically, we show that phosphorylation of cAMP response element-binding protein (CREB), a major regulator of MafA expression, is reduced in islets of obese Ins-G5b–KOs, and we show that this phenotype precedes the downregulation of MafA and MafA target genes. Taken together, GPRC5B helps to maintain mature β cell function in obesity through cAMP/CREB-dependent regulation of MafA expression.

Vascular cells express various G-protein-coupled receptors (GPCRs) with yet unknown function, among them orphan receptor GPR153. GPR153 was upregulated in smooth muscle cells (SMCs) in response to injury, and knockdown of GPR153 resulted in reduced proliferation and mildly altered differentiation in human SMCs. Mice with tamoxifen-inducible, SMC-specific GPR153 deficiency were partially protected against ligation-induced neointima formation, and their SMCs were characterized by reduced proliferation and dedifferentiation. Mechanistically, we show that GPR153 negatively regulates cellular cAMP levels, and thus the absence of GPR153 leads to an increase in CREB phosphorylation, reduced YAP/TAZ levels, and diminished NF-κB activation. Interestingly, a similar role of GPR153 was observed in endothelial cells (ECs), where loss of GPR153 resulted in reduced inflammatory gene expression and protected mice with EC-specific GPR153 deficiency in models of neuroinflammation and stroke. Taken together, orphan receptor GPR153 facilitates pro-inflammatory and pro-proliferative gene expression in ECs and SMCs by controlling cellular cAMP levels, thereby contributing to inflammation and vascular remodeling.

Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial lung disease characterized by the excessive accumulation of activated myofibroblasts that deposit extracellular matrix (ECM) protein, leading to progressive scar formation and mechanical stress. However, the cellular origin and fate of myofibroblasts remain controversial, and the mechanisms by which myofibroblasts sense mechanical cues in the lung are unclear. Here, we report that periostin (Postn) is a reliable and distinctive marker for pulmonary myofibroblasts, while ablation of Postn ⁺ myofibroblasts after injury ameliorated lung fibrosis. PIEZO1 was highly expressed in Postn ⁺ myofibroblast and played a vital role in mechanoactivation of Postn ⁺ myofibroblast and development of lung fibrosis. Conditional deletion of Piezo1 in Postn ⁺ myofibroblasts significantly inhibited lung fibrosis by suppressing myofibroblast activation and proliferation. Loss of Piezo1 led to disruption of actin organization and prevention of Yap/Taz nuclear localization, thus shifting the myofibroblasts from a proliferative state into a stressed and apoptotic state. Furthermore, myofibroblast-specific Yap/Taz deletion fully recapitulated the protective phenotypes of myofibroblast- Piezo1 –KO mice. These findings show that periostin marks pulmonary myofibroblasts, and that PIEZO1-mediated mechanosensation is essential for myofibroblast activation in the lung. Targeting PIEZO1 in the periostin-expressing cells is a novel therapeutic option to interfere with fibrotic diseases such as IPF .

Differentiation of cardiac fibroblasts (CFs) into myofibroblasts (CMFs) is considered a critical event in response to the maladaptive cardiac remodeling triggered by angiotensin II (Ang II). Active CMFs are proliferative and contribute to the production of extracellular matrix and matricellular proteins such as periostin, to myocardial fibrosis, and thus to muscle stiffness. Although previous studies provided substantial evidence for the antifibrotic signaling elicited by NO/NP-cGMP-cGKI, the role of this axis in modulating CMF function(s) in vivo remains unclear. To address this, Ang II was delivered through osmotic minipumps into tamoxifen-induced CMF-specific cGKI knockout (cmfKO) and littermate control (CTR) male mice. CMF-restricted Cre activity in periostin+ cells resulted in an effective depletion of the cGKI protein observed in myocardial sections and in primary CF/CMF protein lysates obtained from Ang II- and tamoxifen-treated cmfKO. Although both genotypes responded identically to Ang II in terms of blood pressure (BP) and cardiac enlargement, cmfKO hearts showed significantly increased cardiomyocyte cross-sectional areas and developed a marked increase in myocardial fibrosis. Moreover, non-invasive echocardiography revealed a structure-related distortion of global systolic function and longitudinal deformation capacity in cmfKO versus CTR. Consistent with the results obtained in vivo, we observed a higher proliferation rate of CF/CMF derived from Ang II-treated cmfKO hearts compared with respective CTR cells, as well as an increase in cardiomyocyte apoptosis in the absence of cGKI in periostin+ CMF. Our data confirm that endogenous cGKI function in periostin+ CMFs counteracts the Ang II-induced morphologic and structural changes that impair cardiomyocyte survival ultimately causing loss of heart function in mice.

The function of islet macrophages is poorly understood. They promote glucose-stimulated insulin secretion (GSIS) in lean mice, however, the underlying mechanism has remained unclear. We show that activation of the free fatty acid receptor FFAR4 on islet macrophages leads to interleukin-6 (IL-6) release and that IL-6 promotes β-cell function. This mechanism is required for GSIS in lean male mice, but does not function anymore in islets from people with obesity and obese type 2 diabetic male mice. In islets from obese mice, FFAR4 downstream signaling in macrophages is strongly reduced, resulting in impaired FFAR4-mediated IL-6 release. However, IL-6 treatment can still improve GSIS in islets from people with obesity and obese type 2 diabetic mice. These data show that a defect in FFAR4-mediated macrophage activation contributes to reduced GSIS in type 2 diabetes and suggest that reactivating islet macrophage FFAR4 and promoting or mimicking IL-6 release from islet macrophages improves GSIS in type 2 diabetes.

Macrophages express numerous G protein-coupled receptors (GPCRs) that regulate adhesion, migration, and activation, but the function of orphan receptor GPRC5B in macrophages is unknown. Both resident peritoneal and bone marrow-derived macrophages from myeloid-specific GPRC5B-deficient mice show increased migration and phagocytosis, resulting in improved bacterial clearance in a peritonitis model. In other models such as myocardial infarction, increased myeloid cell recruitment has adverse effects. Mechanistically, we found that GPRC5B physically interacts with GPCRs of the prostanoid receptor family, resulting in enhanced signaling through the prostaglandin E receptor 2 (EP2). In GPRC5B-deficient macrophages, EP2-mediated anti-inflammatory effects are diminished, resulting in hyperactivity. Using in silico modelling and docking, we identify residues potentially mediating GPRC5B/EP2 dimerization and show that their mutation results in loss of GPRC5B-mediated facilitation of EP2 signaling. Finally, we demonstrate that decoy peptides mimicking the interacting sequence are able to reduce GPRC5B-mediated facilitation of EP2-induced cAMP signaling in macrophages.