Hydroxycarboxylic acid receptor 1 (HCAR1), also known as lactate receptor or GPR81, is a class A G-protein-coupled receptor with key roles in regulating lipid metabolism, neuroprotection, angiogenesis, cardiovascular function, and inflammatory response in humans. HCAR1 is highly expressed in numerous types of cancer cells, where it participates in controlling cancer cell metabolism and defense mechanisms, rendering it an appealing target for cancer therapy. However, the molecular basis of HCAR1-mediated signaling remains poorly understood. Here, we report four cryo-EM structures of human HCAR1 and HCAR2 in complex with the Gi1 protein, in which HCAR1 binds to the subtype-specific agonist CHBA (3.16 Å) and apo form (3.36 Å), and HCAR2 binds to the subtype-specific agonists MK-1903 (2.68 Å) and SCH900271 (3.06 Å). Combined with mutagenesis and cellular functional assays, we elucidate the mechanisms underlying ligand recognition, receptor activation, and G protein coupling of HCAR1. More importantly, the key residues that determine ligand selectivity between HCAR1 and HCAR2 are clarified. On this basis, we further summarize the structural features of agonists that match the orthosteric pockets of HCAR1 and HCAR2. These structural insights are anticipated to greatly accelerate the development of novel HCAR1-targeted drugs, offering a promising avenue for the treatment of various diseases.
Copyright: © 2025 Pan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Accurately imaging adult cardiac tissue in its native state is essential for regenerative medicine and understanding heart disease. Current fluorescence methods encounter challenges with tissue fixation. Here, we introduce the 3D-NaissI (3D-Native Tissue Imaging) method, which enables rapid, cost-effective imaging of fresh cardiac tissue samples in their closest native state, and has been extended to other tissues. We validated the efficacy of 3D-NaissI in preserving cardiac tissue integrity using small biopsies under hypothermic conditions in phosphate-buffered saline, offering unparalleled resolution in confocal microscopy for imaging fluorescent small molecules and antibodies. Compared to conventional histology, 3D-NaissI preserves cardiac tissue architecture and native protein epitopes, facilitating the use of a wide range of commercial antibodies without unmasking strategies. We successfully identified specific cardiac protein expression patterns in cardiomyocytes (CMs) from rodents and humans, including for the first time ACE2 localization in the lateral membrane/T-Tubules and SGTL2 in the sarcoplasmic reticulum. These findings shed light on COVID-19-related cardiac complications and suggest novel explanations for therapeutic benefits of iSGLT2 in HFpEF patients. Additionally, we challenge the notion of "connexin-43 lateralization" in heart pathology, suggesting it may be an artifact of cardiac fixation, as 3D-NaissI clearly revealed native connexin-43 expression at the lateral membrane of healthy CMs. We also discovered previously undocumented periodic ring-like 3D structures formed by pericytes that cover the lateral surfaces of CMs. These structures, positive for laminin-2, delineate a specific spatial architecture of laminin-2 receptors on the CM surface, underscoring the pivotal role of pericytes in CM function. Lastly, 3D-NaissI facilitates the mapping of native human protein expression in fresh cardiac autopsies, offering insights into both pathological and non-pathological contexts. Therefore, 3D-NaissI provides unparalleled insights into native cardiac tissue biology and holds the promise of advancing our understanding of physiology and pathophysiology, surpassing standard histology in both resolution and accuracy.
© 2025. The Author(s).

Cystic fibrosis (CF) is an autosomal recessive disease characterized by microbial infection and progressive decline in lung function, leading to significant morbidity and mortality. The bitter taste receptor T2R14 is a chemosensory receptor that is significantly expressed in airways. Using a combination of cell-based assays and T2R14 knockdown in bronchial epithelial cells from CF and non-CF individuals, we observed that T2R14 plays a crucial role in the detection of bacterial and fungal signals and enhances host innate immune responses. Expression of Gαi protein is enhanced in CF bronchial epithelial cells and T2R14-Gαi specific signaling leads to increased calcium mobilization. Knockdown of T2R14 leads to reduced innate immune activation by bacterial strains deficient in quorum sensing. The results demonstrate that T2R14 helps protect against microbial infection and thus may play an important role in the innate immune defense of the CF airway epithelium.
© 2024 The Author(s).

Abstract Accurately imaging adult cardiac tissue in its native state is essential for regenerative medicine and understanding heart disease. Current fluorescence methods encounter challenges with tissue fixation. Here, we introduce the 3D-NaissI (3D-Native Tissue Imaging) method, enabling rapid, cost-effective imaging of fresh cardiac tissue samples in their closest native state, that we also extended to other tissues. We validated 3D-NaissI’s efficacy in preserving cardiac tissue integrity using small biopsies under hypothermic conditions in phosphate-buffered saline, offering unparalleled resolution in confocal microscopy for imaging fluorescent-small molecules/-antibodies. Compared to conventional histology, 3D-NaissI preserves cardiac tissue architecture and native protein epitopes, facilitating the use of a wide range of commercial antibodies without unmasking strategies. We successfully identified specific cardiac protein expression patterns in cardiomyocytes (CMs) from rodents and humans, including for the first time ACE2 localization in the lateral membrane/T-Tubules and SGTL2 in the sarcoplasmic reticulum. These findings shed light on COVID-19-related cardiac complications and suggest novel explanations for iSGLT2 therapeutic benefits in HFpEF patients. Additionally, we challenge the notion of "connexin-43 lateralization” in heart pathology, suggesting it may be an artifact of cardiac fixation, as 3D-NaissI clearly revealed native connexin-43 expression at the lateral membrane of healthy CMs. We also discovered previously undocumented periodic ring-like 3D structures formed by pericytes covering CMs’ lateral surfaces. These structures, positive for laminin-2, delineate a specific spatial architecture of laminin-2 receptors at the CM surface, highlighting the pivotal role of pericytes in CM function. Lastly, 3D-NaissI facilitates mapping native human protein expression in fresh cardiac autopsies, providing insights into both pathological and non-pathological contexts. Hence, 3D-NaissI offers unparalleled insights into native cardiac tissue biology and promises to advance our understanding of physiology and pathophysiology, surpassing standard histology in resolution and accuracy.

The development of new μ-opioid receptor (MOR) agonists without the undesirable side effects, such as addiction or respiratory depression, has been a difficult challenge over the years. In the search for new compounds, we screened our chemical database of over 40.000 substances and further assessed the best 100 through molecular docking. We selected the top 10 compounds and evaluated them for their biological activity and potential to influence cyclic adenosine monophosphate (cAMP) levels. From the tested compounds, compound 7, called aniquinazoline B, belonging to the quinazolinone alkaloids class and isolated from the marine fungus Aspergillus nidulans, showed promising results, by inhibiting cAMP levels and in vitro binding to MOR, verified through microscale thermophoresis. Transcriptomic data investigation profiled the genes affected by compound 7 and discovered activation of different pathways compared to opioids. The western blot analysis revealed compound 7 as a balanced ligand, activating both p-ERK1/2 and β-arrestin1/2 pathways, showing this is a favorable candidate to be further tested.
© 2024 Wiley-VCH GmbH.