Cardiovascular disease currently tops the list of human mortality causes, with various factors contributing to heart failure. Pathological stimuli such as hypertension and thrombosis often lead to cardiac hypertrophy, a significant trigger for heart failure. Therefore, inhibiting and reversing pathological cardiac hypertrophy, as well as slowing down myocardial remodeling, are crucial. The discovery of new targets and the development of innovative drugs are urgently needed.
Professor Zhang Yan's research team at the School of Medicine, Zhejiang University, in collaboration with Professor Zhang Yan's team at the School of Basic Medical Sciences, Peking University, have jointly conducted research. They have utilized precision structural design to develop effective regulators of apelin receptors, which significantly improve cardiac hypertrophy. This breakthrough offers a novel strategy for the precise targeting and improvement of cardiovascular disease medications.
On March 1st, this achievement was published in the journal Cell.
Design Concept and Myocardial Protection Activity of Novel APLNR Biased Agonist WN561 (Image provided by Zhejiang University)
Cracking the Dilemma of Drug Target "Bipolarity"
G Protein-Coupled Receptors (GPCRs), as the name suggests, are receptors that "work only when connected to G proteins." Located on the cell membrane, they participate in regulating most physiological functions and are often studied as drug targets. Apelin, the endogenous ligand of A-type G protein-coupled receptor (APLNR), can activate both G protein and β-arrestin signaling pathways downstream of APLNR, regulating various physiological and pathological processes. Particularly in the cardiovascular system, APLNR activation promotes vasodilation, positive inotropy, angiogenesis, diuresis, blood pressure reduction, and also participates in the pathophysiological regulation of cardiovascular diseases, such as inhibiting cardiac fibrosis, reducing pathological myocardial hypertrophy, resisting heart failure, and pulmonary arterial hypertension, making it a promising target for cardiovascular disease intervention. However, the cardioprotective effect induced by the endogenous ligand apelin is mainly attributed to its Gi signaling, while simultaneous activation of the β-arrestin signal can cause harmful myocardial hypertrophy in healthy hearts, weakening the efficacy of drugs.
It is this "bipolarity" that has perplexed scientists, with both positive effects and adverse effects coexisting, severely affecting the effectiveness and safety of drugs. Many internationally renowned pharmaceutical companies and research institutions have been attempting to develop safe and effective APLNR agonists, but to date, no precisely targeted drug molecule has been approved for marketing.
Zhang Yan's team at Zhejiang University has long been committed to the mechanism research of transmembrane signal transduction and the design of precise regulation methods, and has developed and established a series of innovative methods based on the cryo-electron microscopy of GPCR pharmacology, achieving precise intervention in diseases based on structural design to finely regulate GPCR function.
The Zhang Yan team at Peking University has always focused on the mechanism of myocardial injury and its role in cardiovascular diseases, developing targeted research on disease prevention and treatment targets and interventions, providing new strategies for the prevention and treatment of clinical cardiovascular diseases. Two scholars with the same name and surname began a relay collaboration research.
Unveiling the Mystery of Downstream Signal Activation by Different Signal Spectrum Agonists
The first step of the research was to unveil how different signal spectrum agonists activate receptor-mediated downstream signals. The team compared three agonists to "spot the differences" and used cryo-electron microscopy to resolve the high-resolution structures of the APLNR-Gi1 complex recognized by the endogenous balanced agonist apelin and the two partial G protein-biased agonists MM07 and CMF-019. The results showed that the APLNR-Gi1 complexes bound by these three agonists looked very similar, like "triplets," with seemingly no difference in appearance.
However, the research team did not give up. After repeated experiments, they finally identified subtle differences. If the ligand is compared to a key and the receptor to a lock, the top of apelin, i.e., the key handle, is relatively extended, while the key handle of MM07 forms a loop, resulting in differences in the depth and specific position of the insertion of their key bodies into the receptor lock core. They defined the two key sites, M11 and F13, inserted into two pockets as "dual hotspots," which are crucial for biased signal transduction.
This difference in ligand-binding pockets is transmitted to the downstream effector protein-binding pockets, resulting in crucial changes in signal transduction—the D752.50 located at the center of the polarity network acts as a switch for biased signals, resulting in a structural shift of 0.1 nanometers. It is this minute difference, equivalent to one-millionth of the diameter of a hair, that leads to different conformational rearrangements of the downstream effector protein-binding pockets, ultimately determining whether Gi signaling or β-arrestin signaling is activated.
Zhang Yan of Zhejiang University said, "After revealing how different biased signal molecules recognize and activate APLNR, we designed G protein-biased agonists WN353 and WN561 targetedly, while eliminating the activity of β-arrestin."
Customized Targeted Drugs on the Horizon
To avoid interference, the team mixed the newly designed agonists with existing agonists in the market and randomized the numbering, conducting "double-blind" functional screening and verification using in vitro cultured myocardial cells and in vivo animal models of heart disease. Dr. Wang Weiwei of Zhejiang University said, "During the 'unblinding' online meeting, the tension was palpable. The results perfectly showed that our designed completely G protein-biased agonists WN353 and WN561 did not cause myocardial hypertrophy as side effects. Our experiments once again confirmed that the β-arrestin signaling pathway of APLNR is indeed the main pathway leading to myocardial hypertrophy."
Subsequently, researchers simulated the therapeutic effects of APLNR agonists in conditions with myocardial hypertrophy but without pathological stimuli, such as patients with valve disease or hypertension. The results confirmed that Apelin aggravated myocardial hypertrophy, while MM07 and CMF-019 had no effect. Encouragingly, the newly developed agonist WN561 improved mouse myocardial hypertrophy under conditions with or without pathological stimuli, further demonstrating the promising prospects of this novel G protein-biased APLNR agonist in treating myocardial hypertrophy and heart failure.
This research reveals the recognition characteristics of APLNR complexes with different biased ligands and successfully rationalizes the design of APLNR agonists with absolute G protein signal selectivity. Through three animal models, the safety and effectiveness of newly designed active molecules are demonstrated, providing a new strategy for the development of drugs targeting APLNR to improve cardiovascular diseases.
Zhang Yan of Zhejiang University said that perhaps in the near future, drugs that can "reduce fat and enhance efficiency" for the myocardium can be "customized," helping cardiovascular patients to "bloom with joy" again.
Related Paper Information:
