Neurons in the brain build circuits by synapsing with each other, and glial cells are involved in the formation and elimination of synapses. Glial cells include microglia, astrocytes, and oligodendrocytes, each with distinctive functions supported by different gene expression patterns and morphologies, but all have been shown to regulate the number of synapses in the neuronal circuits through a common function, synaptic phagocytosis. It has also been reported that specific glial cell types phagocytose specific synapses in different brain regions and at different times, and some of the molecular mechanisms involved in each phagocytotic process have been elucidated. For example, microglia, the most frequently reported glial cell type in relation to synaptic phagocytes, are known to recognize various “eat me signals” including complement and phagocytose synapses, contributing to the refinement of neuronal circuits during development. More recently, astrocytes and oligodendrocyte precursor cells have also been shown to be involved in synaptic phagocytosis. Interestingly, there are also reports of different types of glial cells phagocytosing the same types of synapses. And in some cases, it has been suggested that different glial cell types regulate each other’s synaptic phagocytosis. In this review, we will discuss the significance of synaptic phagocytosis by multiple types of glial cells by presenting recent studies on synaptic phagocytosis by glial cells.

Microglia are the immune cells of the central nervous system. They play an important role in maintaining brain homeostasis by constantly surveying their surrounding microenvironment. During pathological event in the brain, microglia respond quickly to restore homeostasis by clearing damaged cells and secreting various proinflammatory mediators. However, during chronic inflammation, their homeostatic functions is lost and they secrete various proinflammatory cytokines and mediators that induce neural dysfunction and neurodegeneration. These microglia mediated tissue damage plays an important role in pathogenesis of various neurological disorders like Alzheimer’s disease and Parkinson's disease. Microglia require colony receptor factor 1 receptor (CSF1R)-mediated signals for their survival. Recently, CSF1R antagonist has been used to deplete microglia, reset microglia by forced depletion and repopulation or depletion followed by transplantation with new microglia as a therapeutic strategy for various neurological disorders. In this article, we describe the role of microglia in the in various neurological disorders, and discuss potential therapeutic strategy to manipulate microglia by depletion, resetting and transplantation.

Microglia are the only immune cells in the central nervous system. It has been shown that microglia actively regulate the number of neurons by participating in the cell death of neural stem cells during development and maturation. In addition, recent optical techniques have enabled in vivo imaging, which has revealed the function of microglia on synapses. Microglia regularly monitor synaptic activity and remove synapses that show abnormal activity in the event of brain infarction or other disorders. During development, microglia contribute to the formation of immature synapses by contacting dendrites during early synapse formation, and they are also involved in the de-synaptic process by selectively removing weakly active synapses through the use of classical complement cascade signaling. Furthermore, these abnormalities are known to contribute to the development of autism during development and to the development of Alzheimer's disease during maturation. In addition to this, microglia also contribute to plastic changes in synapses during the learning process in maturation. Furthermore, by modifying synaptic activity, microglia are known to be involved in changes in the activity of neuronal circuits. In addition to these synaptic functions, microglia are also known to be involved in the permeability of the blood-brain barrier. In this chapter, these functions will be summarized and discussed.

Lesion or diseases affecting the somatosensory system causes neuropathic pain, a debilitating chronic pain condition. Previous studies using its experimental models have demonstrated the critical contribution of microglia to the development of neuropathic pain. Upon sensing nerve damage, spinal cord microglia alter their morphology, gene expression and function, which lead to an increase in the excitability of pain-transmission neural pathway, causing the pain onset. Recently, newly identified CD11c-positive microglia as a subset that increases during the remission phase of neuropathic pain has been shown to be required for spontaneous remission of neuropathic pain and to play an important role in maintaining the remission state. Thus, these findings suggest that the functions and roles of microglia under neuropathic pain conditions are not one-dimensional but change during the onset, maintenance, and remission phases, and they also provide a clue to establish a new strategy to decipher neuropathic pain and other neurological diseases from the heterogeneity of microglia.

Cardiovascular disease is a major cause of death worldwide, with high prevalence and morbidity. Recent advances in technology have reported that abnormalities in the gut microbiota are associated with a variety of diseases, including cardiovascular diseases. The gut microbiota is a complex ecosystem that plays an important role in maintaining host health. It has been reported that the imbalance of gut microbiota causes changes in the production of substances derived from gut bacteria, such as short-chain fatty acids, trimethylamine-N-oxide, and lipopolysaccharide, and contributes to the development of cardiovascular diseases. In the drug discovery, it is a promising approach to prevention and therapy of the cardiovascular disease to focus on the relation between gut and heart, such as gut bacteria. However, there are challenges that must be overcome to convert this approach into effective therapy. In this review, we focus on cardiovascular diseases, particularly atherosclerotic disease, heart failure, and atrial fibrillation, and discuss the relationship between gut bacteria and substances derived from gut bacteria in cardiovascular disease. We also discuss the challenges and potential of drug discovery targeting the gut-heart relationship for the treatment and prevention of cardiovascular disease.

The role of the nitric oxide synthases (NOSs) system in inter-organ communication is not fully understood. We addressed this point in our mice lacking all three NOS isoforms (triple n/i/eNOSs^−/− mice). We previously reported that the triple n/i/eNOSs^−/− mice spontaneously develop myocardial infarction. However, it takes a long time (approximately 1 year) to develop myocardial infarction. We then revealed that 2/3-nephrectomized triple n/i/eNOSs^−/− mice suddenly die due to early onset of myocardial infarction, succeeding in developing an experimentally useful model of myocardial infarction. These results suggest the protective role of NOSs in reno-cardiac communication. We next studied the role of NOSs in bone marrow cells (BM) in vascular lesion formation. Constrictive vascular remodeling and neointimal formation at 14 days after carotid artery ligation were markedly accelerated in wild-type (WT) mice transplanted with triple n/i/eNOSs^−/− BM as compared with those with WT BM. These results suggest the protective role of NOSs in BM-vascular communication. We then investigated the role of NOSs in BM in pulmonary hypertension (PH). The extents of PH at 3 weeks after hypoxic exposure were markedly exacerbated in WT mice transplanted with triple n/i/eNOSs^−/− BM as compared with those with WT BM, suggesting the protective role of NOSs in BM-lung communication. These lines of evidence indicate that systemic and BM NOSs may be a novel therapeutic target in MI, vascular disease, and PH.

The production of angiotensin II (Ang II) in the brain plays important roles as neurotransmitter and neuropeptide. Central Ang II is involved in regulating various physiological processes, such as blood pressure and water homeostasis, via Ang II type 1 (AT1) receptors. We have demonstrated that Ang II induces frequent urination via AT1 receptors in the brain even at doses that does not seem to affect the blood pressure in animal experiment. Intracerebroventricular administration of Ang II was also found to reduce the bladder capacity without affecting the maximum voiding pressure, post voiding residual urine volume or voiding efficiency. Additionally, the activation of AT1 receptor downstream signal pathway (phospholipase C/protein kinase C/NADPH oxidase/superoxide anion) and suppression of GABAergic nervous system in the brain are involved in the mechanism underlying the central Ang II-inducted frequent urination. AT1 receptor blockers (ARBs) have been widely used to treat hypertension. We demonstrated that peripherally administered ARBs telmisartan, which can penetrate blood-brain barrier, exerted an inhibitory effect on central Ang II-inducted frequent urination. We present the possible drug therapy targeting AT1 receptors in the brain against frequent urination on the results obtained from our recent research work.

Cyfuse Biomedical K.K. is a R&D venture company established in 2010 aiming at industrialization of its 3D cellular products for regenerative medicine based on innovative 3D cell stacking technology, and has newly listed on the Growth Market of the Tokyo Stock Exchange in December 2022. We are developing 3D cellular products consisted of only human cells through our unique platform technology created from the fusion of two disparate technologies; engineering and biology. Three pipelines aiming for approval as products for regenerative medicine have already advanced to the stage of human clinical trials, and are expected to implemented in society in the near future. In addition, we also have been developing functional cellular devices (FCD) using our core technology, the Kenzan method, and have begun marketing FCD as support tools that contribute to the development of new drugs. We will introduce in detail our contribution to the medical field that we are aiming for, with specific examples, also referring to the unique additive manufacturing (AM) technology that supports the realization of our cellular products as above.

Sotorasib (LUMAKRAS^®) is the first RAS inhibitor that selectively binds to KRAS G12C and irreversibly inhibits the conformational change from the inactive to active form of KRAS. The gene mutation that produces KRAS G12C protein, which is the target of sotorasib, is one of the oncogenic drivers observed in non-small cell lung cancer (NSCLC), and the KRAS G12C mutation causes conformational changes to maintain KRAS in an active form enhancing downstream signals, leading to tumor cell proliferation and survival. Although the role of KRAS in human cancers has been known for decades, role of RAS in normal cells, the high affinity between RAS and GTP, high concentration of intracellular GTP, and the smooth surface of RAS protein makes it difficult to develop drugs targeting RAS mutation for a long time. However, the discovery of the Switch II pocket of KRAS in 2013 and the report of compounds that specifically bind to KRAS G12C led to the development of sotorasib. Sotorasib inhibited the growth of KRAS G12C positive cell lines and suppressed tumor growth in a mouse model implanted with the KRAS G12C positive cell line. In clinical trials, objective responses were seen in 37.4% of patients with KRAS G12C positive advanced NSCLC taking 960mg sotorasib orally per day. There were no dose-limiting toxicities and other adverse events were tolerable. Sotorasib was designated as an orphan drug in March 2021 and approved in January 2022 for KRAS G12C positive unresectable/recurrent NSCLC that has progressed after 1st line therapy in Japan.

Avacopan (TAVNEOS^® capsules) is an orally available selective C5a receptor (C5aR) antagonist. It has been approved in Japan since 2021 for the treatment of microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA), the two major subtypes of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The current standard therapy combining glucocorticoids (GC) and immunosuppressants has greatly improved the prognosis of AAV, however, issues such as side effects associated with GC use remain to be resolved. Avacopan suppresses priming of neutrophils induced by the complement component C5a, a process deeply involved in the pathogenesis of AAV. In pre-clinical studies, avacopan inhibited chemotaxis and priming of neutrophils induced by C5a-C5aR signaling. It also significantly suppressed nephritis and renal damage in an ANCA-induced glomerulonephritis mouse model. In the global phase 3 study “ADVOCATE”, avacopan achieved both primary endpoints being 1) non-inferior to prednisone in inducing remission at week 26 and 2) superior in sustained remission at week 52 for MPA and GPA patients. Additionally, with avacopan, GC toxicity score was significantly lower and fewer adverse events possibly related to GC were observed. Furthermore, avacopan increased estimated glomerular filtration rate (eGFR) more than prednisone indicating improved renal function. Thus, the novel mechanism of avacopan targeting the complement system is a promising new therapeutic option for AAV with fewer GC-related side effects and better improvement of renal function.

Darinaparsin, an active ingredient of DARVIAS^® Injection 135 ‍mg, is a novel organic arsenical compound of dimethylated arsenic conjugated to glutathione. Darinaparsin is thought to induce apoptosis and cell-cycle arrest and suppress tumor growth by disrupting mitochondrial functions and increasing production of intracellular reactive oxygen species. Darinaparsin is processed at the cell surface by γ-glutamyltranspeptidase (γ-GT), leading to formation of dimethylarsino-cysteine, which is imported via a cystine transporter expressed on cell surface membranes. Numerous tumor cells express high levels of γ-GT and cystine transporter, to maintain high levels of glutathione as an intracellular antioxidant. Darinaparsin is a novel antineoplastic agent designed to exploit the characteristics of tumor cells and to be efficiently taken up by tumor cells to inhibit their growth. In a global phase 2 pivotal study of darinaparsin in Asian patients with relapsed or refractory peripheral T-cell lymphoma (r/r PTCL), the overall response rate was 19.3% (90% confidence interval: 11.2–29.9%) and grade ≥3 drug-related adverse events with an incidence rate ≥5% included neutropenia (9.2%, n = 6), anemia (6.2%, n = 4) and thrombocytopenia (6.2%, n = 4) in 65 patients receiving darinaparsin. Based on the results of this phase 2 trial, which demonstrated the anti-tumor activity and acceptable safety profile of darinaparsin in patients with r/r PTCL, Solasia pharma K.K. received approval for darinaparsin for the treatment of r/r PTCL in June 2022, and Nippon Kayaku Co., Ltd. launched this drug in August 2022. Darinaparsin is expected to contribute to the clinical practice of PTCL as a new treatment option for this disease.