Folia Pharmacologica Japonica最新文献

Regulation of thermogenesis in mammals is essential for maintaining body temperature homeostasis under fluctuating environmental temperature. Impairments in this regulation can lead to severe conditions, including fever or heatstroke. This review focuses on malignant hyperthermia (MH), a pathological escalation of thermogenesis in skeletal muscle. It highlights the role of type 1 ryanodine receptor (RYR1), a Ca²⁺ release channel, based on our recent studies. Previous studies have revealed that genetic mutations in RYR1 are associated with muscle disorders including MH, which are characterized by abnormal Ca²⁺-induced Ca²⁺ release (CICR). To test our hypothesis that RYR1 channel function is closely related to thermogenesis, we examined cultured cell lines expressing wild-type or MH-related mutants of RYR1, as well as muscle cells prepared from MH model mice. Using a local heating microscopy combined with fluorescence temperature imaging, we identified a novel phenomenon termed heat-induced Ca²⁺ release (HICR). Furthermore, our results indicate that anesthesia induces simultaneous increases in temperature and cytoplasmic Ca²⁺ concentration in muscle cells. Based on these findings, we propose a positive feedback loop where HICR drives further Ca²⁺ release during MH episodes, causing thermogenesis and further elevation of body temperature. This review summarizes our experimental results that were presented at the symposium, providing greater detail on the mechanisms underlying MH pathogenesis and the role of RYR1 in thermal regulation.

Fluorescent biosensors have become essential tools in life sciences, enabling the visualization of the spatiotemporal dynamics of signaling molecules at the cellular level. In particular, intensity-based sensors-where changes in the concentrations of signaling molecules are detected as changes in fluorescence intensity-are widely used due to their versatility. However, such sensors are often affected by several factors, including variations in biosensor concentration, photobleaching, optical path settings, and focus drift, which hamper quantitative analysis. To overcome these challenges, we have been developing fluorescence lifetime imaging microscopy (FLIM)-based biosensors that utilize fluorescence lifetime-a parameter independent of probe concentration and imaging conditions-as a robust and reliable readout. Our research has focused on the quantitative visualization of physiological parameters, particularly those relevant to skeletal muscle homeostasis and ion channel activity. One example is a small-molecule fluorescent temperature sensor designed to quantify temperature changes in subcellular compartments. This sensor, based on an organic dye, enables targeting to organelle membranes and provides high spatial resolution, allowing precise detection of local heat production, such as that occurring in the mitochondria of brown adipocytes. In parallel, we have developed genetically encoded fluorescent protein-based sensors that correlate fluorescence lifetime values with the concentrations of signaling molecules such as ATP. These sensors have enabled the quantitative imaging of ATP dynamics in various cell types and multicellular systems. Furthermore, we are constructing a flexible sensor development platform, paving the way for the creation of diverse biosensors that can contribute to comprehensive studies in muscle physiology.

Stressful experiences can initiate or exacerbate mental health conditions, including depression. Depression is a complex and diverse syndrome characterized by varying symptom profiles, progression patterns, and responses to treatment. Despite this, the specific mechanisms by which prolonged stress leads to individual differences in behavior remain poorly understood. A major obstacle in advancing our understanding of the neurobiological and pathological consequences of psychosocial stress is the absence of subtype-based approaches in preclinical models. To address this gap, we implemented a behavioral subtyping strategy in preclinical research to explore how stress-induced behavioral variability is shaped by neural circuits, cellular processes, and molecular mechanisms. Using this approach, we classified stressed male mice into four distinct behavioral subtypes, based on their manifestations of social withdrawal and anhedonia-key features of many psychiatric disorders. Our findings revealed that three neural projection pathways originating from the prefrontal cortex play crucial roles in mediating these stress-related behaviors. In particular, the pathway connecting the medial prefrontal cortex (mPFC) to the anterior paraventricular thalamus (aPVT) was shown to influence a behavioral subtype marked by both social deficits and anhedonia. Moreover, we uncovered a molecular mechanism at the circuit level that underlies this specific phenotype: epigenetic repression of the Shisa2 gene by KDM5C within aPVT-projecting neurons in the mPFC contributes to the emergence of these behavioral impairments. Our research thus highlights distinct biological factors-spanning cellular, molecular, and epigenetic levels-that contribute to individual differences in stress-induced behavioral outcomes.

Histamine plays a crucial role in maintaining wakefulness. Decreased histamine levels in the cerebrospinal fluid have been reported in patients with hypersomnia, including narcolepsy and idiopathic hypersomnia. Histamine N-methyltransferase (HNMT) is a key enzyme responsible for histamine degradation in the brain. In this study, we examined the effects of pharmacological HNMT inhibition on animal models of hypersomnia disorders. Metoprine, an HNMT inhibitor, significantly increased brain histamine levels and produced robust wake-promoting effects and suppressed cataplexy in narcolepsy model mice. The arousal effects of metoprine were mainly mediated through activation of histamine H1 receptors. Metoprine also promoted wakefulness in Sleepy mice, a model of idiopathic hypersomnia, and in drug-induced Parkinson's disease model mice. Compared with pitolisant, an H3 receptor inverse agonist that has been approved in EU and US for treatment of narcolepsy, metoprine exhibited stronger and more sustained wake-promoting effects. Our findings indicate that HNMT inhibitors increase brain histamine levels and promote wakefulness in various types of hypersomnia. Therefore, HNMT inhibitors may represent a novel and effective therapeutic approach for hypersomnia. To further advance drug development, we have performed high-throughput screening based on mass spectrometry, through which approximately 1,000 hit compounds have been identified.