Structural determinants of the propofol binding site in HCN1

Around 10-25% of the global population suffers chronic pain. Chronic pain is defined as pain that outlasts the cue despite its termination and that persists for more than 12 weeks. The reasons for chronic pain are diverse but are often linked to pathological changes in the nervous system of the pain signal pathway resulting in the amplification of signals. A survey of chronic pain patients in Europe showed that 40% of the patients found their pain treatment insufficient. Since the causes of chronic pain are multifaceted, the classical therapeutic regime needs to be expanded and tailored to the patients to ensure effective treatment. In addition to their sedative effect, anaesthetics such as propofol alleviate pain. The mechanism driving the analgetic action, however, is not fully understood. Propofol was shown to inhibit several ion channel types that are involved in pain signalling. Among those ion channels, HCN1 is of particular interest because it was shown to be upregulated in chronic pain. HCN1 channels belong to the hyperpolarization-activated cyclic nucleotide-gating ion channel family (HCN) comprising 4 members (HCN1-4). This channel family is crucial in generating pace-making signals in the heart and brain. Currently, there are no drugs available that target the HCN1 channel specifically while having no effect on the heart specific HCN4 channel. Therefore, HCN1 channels are not considered a suitable therapeutic target in pain treatment. In order to include the HCN1 channel in the treatment spectrum of chronic pain, the development of HCN1-specific compounds is needed. While propofol is not suited for pain medication, due to its lack of specificity and sedative effects, it might serve as template for future HCN1-specific drugs. This is because propofol inhibits the HCN1 channel more effectively than other members of the HCN-ion channel family. In this study we aim to localize the propofol binding site in the HCN1 channel. The identification of the structural elements that shape the propofol binding site will advance our understanding of the mechanism of action of propofol on this channel. This will be crucial for designing a HCN1-dircted drugs will increase the therapeutic range in pain management.

Around 10-25% of the global population suffers from chronic pain, which is defined as pain that persists for more than 12 weeks after the initial cause has resolved. The reasons for chronic pain are diverse, but it is often linked to pathological changes in the nervous system, resulting in the amplification of pain signals. A survey of chronic pain patients in Europe revealed that 40% found their pain treatment insufficient. Given the multifaceted nature of chronic pain, classical therapeutic approaches need to be expanded and tailored to individual patients to ensure effective treatment. In addition to their sedative effects, anesthetics such as propofol also alleviate pain. However, the mechanisms driving the analgesic action of propofol are not fully understood. Propofol has been shown to inhibit several ion channel types involved in pain signaling. Among these, HCN1 channels are of particular interest, as they are upregulated in chronic pain conditions. HCN1 channels belong to the hyperpolarization-activated cyclic nucleotide-gated ion channel family (HCN), which comprises four members (HCN1-4). This channel family is crucial for generating pacemaking signals in the heart and brain. Currently, there are no drugs available that specifically target HCN1 channels without affecting the heart-specific HCN4 channels, thus making HCN1 an unsuitable therapeutic target for pain treatment. The development of HCN1-specific compounds is therefore necessary to include HCN1 channels in the treatment spectrum for chronic pain. Propofol has been shown to inhibit HCN1 channels more efficiently than other isoforms of the same channel family. While propofol itself is unsuitable for pain medication due to its lack of specificity and sedative effects, we used it as a tool to identify unique binding sites on HCN1 channels. Our research demonstrated that propofol binds to a specific pocket delimited by helices of the voltage-sensing domain. Mutagenesis-based perturbation of the binding constituents rendered HCN1 channels insensitive to propofol, providing additional proof that the identified binding site is pharmacologically relevant. This binding site presents a promising target for the development of future drugs. Through drug-screening libraries targeting this site, we may discover new treatments for chronic pain that are both effective and selective.