Endogenous chondroitin extends the lifespan and healthspan in C. elegans.

Chondroitin, a class of glycosaminoglycan polysaccharides, is found as proteoglycans in the extracellular matrix, plays a crucial role in tissue morphogenesis during development and axonal regeneration. Ingestion of chondroitin prolongs the lifespan of C. elegans. However, the roles of endogenous chondroitin in regulating lifespan and healthspan mostly remain to be investigated. Here, we demonstrate that a gain-of-function mutation in MIG-22, the chondroitin polymerizing factor (ChPF), results in elevated chondroitin levels and a significant extension of both the lifespan and healthspan in C. elegans. Importantly, the remarkable longevity observed in mig-22(gf) mutants is dependent on SQV-5/chondroitin synthase (ChSy), highlighting the pivotal role of chondroitin in controlling both lifespan and healthspan. Additionally, the mig-22(gf) mutation effectively suppresses the reduced healthspan associated with the loss of MIG-17/ADAMTS metalloprotease, a crucial for factor in basement membrane (BM) remodeling. Our findings suggest that chondroitin functions in the control of healthspan downstream of MIG-17, while regulating lifespan through a pathway independent of MIG-17.

Inhibition of Transglutaminase 2 Reduces Peritoneal Injury in a Chlorhexidine-Induced Peritoneal Fibrosis Model.

Long-term peritoneal dialysis (PD) is often associated with peritoneal dysfunction leading to withdrawal from PD. The characteristic pathologic features of peritoneal dysfunction are widely attributed to peritoneal fibrosis and angiogenesis. The detailed mechanisms remain unclear, and treatment targets in clinical settings have yet to be identified. We investigated transglutaminase 2 (TG2) as a possible novel therapeutic target for peritoneal injury. TG2 and fibrosis, inflammation, and angiogenesis were investigated in a chlorhexidine gluconate (CG)-induced model of peritoneal inflammation and fibrosis, representing a noninfectious model of PD-related peritonitis. Transforming growth factor (TGF)-ß type I receptor (TGFßR-I) inhibitor and TG2-knockout mice were used for TGF-ß and TG2 inhibition studies, respectively. Double immunostaining was performed to identify cells expressing TG2 and endothelial-mesenchymal transition (EndMT). In the rat CG model of peritoneal fibrosis, in situ TG2 activity and protein expression increased during the development of peritoneal fibrosis, as well as increases in peritoneal thickness and numbers of blood vessels and macrophages. TGFßR-I inhibitor suppressed TG2 activity and protein expression, as well as peritoneal fibrosis and angiogenesis. TGF-ß1 expression, peritoneal fibrosis, and angiogenesis were suppressed in TG2-knockout mice. TG2 activity was detected by α-smooth muscle actin-positive myofibroblasts, CD31-positive endothelial cells, and ED-1-positive macrophages. CD31-positive endothelial cells in the CG model were α-smooth muscle actin-positive, vimentin-positive, and vascular endothelial-cadherin-negative, suggesting EndMT. In the CG model, EndMT was suppressed in TG2-knockout mice. TG2 was involved in the interactive regulation of TGF-ß. As inhibition of TG2 reduced peritoneal fibrosis, angiogenesis, and inflammation associated with TGF-ß and vascular endothelial growth factor-A suppression, TG2 may provide a new therapeutic target for ameliorating peritoneal injuries in PD.

A synthetic synaptic organizer protein restores glutamatergic neuronal circuits.

Neuronal synapses undergo structural and functional changes throughout life, which are essential for nervous system physiology. However, these changes may also perturb the excitatory-inhibitory neurotransmission balance and trigger neuropsychiatric and neurological disorders. Molecular tools to restore this balance are highly desirable. Here, we designed and characterized CPTX, a synthetic synaptic organizer combining structural elements from cerebellin-1 and neuronal pentraxin-1. CPTX can interact with presynaptic neurexins and postsynaptic AMPA-type ionotropic glutamate receptors and induced the formation of excitatory synapses both in vitro and in vivo. CPTX restored synaptic functions, motor coordination, spatial and contextual memories, and locomotion in mouse models for cerebellar ataxia, Alzheimer's disease, and spinal cord injury, respectively. Thus, CPTX represents a prototype for structure-guided biologics that can efficiently repair or remodel neuronal circuits.

The Caenorhabditis elegans INX-4/Innexin is required for the fine-tuning of temperature orientation in thermotaxis behavior.

Innexins in invertebrates are considered to play roles similar to those of connexins and pannexins in vertebrates. However, it remains poorly understood how innexins function in biological phenomena including their function in the nervous systems. Here, we identified inx-4, a member of the innexin family in C. elegans, by a forward screening of thermotaxis-defective mutants. The inx-4 mutants exhibited abnormal migration to a temperature slightly higher than the cultivation temperature, called mild thermophilic behavior. Rescue experiments revealed that INX-4 acts in the major thermosensory neuron AFD to regulate thermotaxis behavior. INX-4::GFP fusion protein localized exclusively along axons in AFD neurons. In addition, over-expression of INX-4 in AFD neurons induced a cryophilic behavior, which is opposite to inx-4 mutants. Our findings suggest that INX-4/Innexin in AFD may fine-tune the execution of thermotaxis behavior when moving to desired temperatures.

Lifespan extension by peroxidase and dual oxidase-mediated ROS signaling through pyrroloquinoline quinone in C. elegans.

Reactive oxygen species (ROS), originally characterized based on their harmful effects on cells or organisms, are now recognized as important signal molecules regulating various biological processes. In particular, low levels of ROS released from mitochondria extend lifespan. Here, we identified a novel mechanism of generating appropriate levels of ROS at the plasma membrane through a peroxidase and dual oxidase (DUOX) system, which could extend lifespan in Caenorhabditis elegans A redox co-factor, pyrroloquinoline quinone (PQQ), activates the C. elegans DUOX protein BLI-3 to produce the ROS H2O2 at the plasma membrane, which is subsequently degraded by peroxidase (MLT-7), eventually ensuring adequate levels of ROS. These ROS signals are transduced mainly by the oxidative stress transcriptional factors SKN-1 (Nrf2 or NFE2L2 in mammals) and JUN-1, and partially by DAF-16 (a FOXO protein homolog). Cell biology experiments demonstrated a similarity between the mechanisms of PQQ-induced activation of human DUOX1 and DUOX2 and that of C. elegans BLI-3, suggesting that DUOXs are potential targets of intervention for lifespan extension. We propose that low levels of ROS, fine-tuned by the peroxidase and dual oxidase system at the plasma membrane, act as second messengers to extend lifespan by the effect of hormesis.

Japanese studies on neural circuits and behavior of Caenorhabditis elegans.

The nematode Caenorhabditis elegans is an ideal organism for studying neural plasticity and animal behaviors. A total of 302 neurons of a C. elegans hermaphrodite have been classified into 118 neuronal groups. This simple neural circuit provides a solid basis for understanding the mechanisms of the brains of higher animals, including humans. Recent studies that employ modern imaging and manipulation techniques enable researchers to study the dynamic properties of nervous systems with great precision. Behavioral and molecular genetic analyses of this tiny animal have contributed greatly to the advancement of neural circuit research. Here, we will review the recent studies on the neural circuits of C. elegans that have been conducted in Japan. Several laboratories have established unique and clever methods to study the underlying neuronal substrates of behavioral regulation in C. elegans. The technological advances applied to studies of C. elegans have allowed new approaches for the studies of complex neural systems. Through reviewing the studies on the neuronal circuits of C. elegans in Japan, we will analyze and discuss the directions of neural circuit studies.

Behavioral plasticity, learning, and memory in C. elegans.

Caenorhabditis elegans exhibits behavior plasticity that appears to correspond to non-associative and associative learning, and short-term and long-term memory. Recent finding revealed that evolutionally conserved molecules such as insulin, monoamines, and neuropeptides are required for the plasticity. We propose the concept of human brain operation from the C. elegans studies.

Thermotaxis of C. elegans as a model for temperature perception, neural information processing and neural plasticity.

Thermotaxis is a model to elucidate how nervous systems sense and memorize environmental conditions to regulate behavioral strategies in Caenorhabditis elegans. The genetic and neural imaging analyses revealed molecular and cellular bases of this experience-dependent behavior. Surprisingly, thermosensory neurons themselves memorize the sensed temperatures. Recently developed techniques for optical manipulation of neuronal activity have facilitated the revelation that there is a sophisticated information flow between sensory neurons and interneurons. Further studies on thermotaxis will allow us to understand the fundamental logics of neural processing from sensory perceptions to behavioral outputs.

A seven-transmembrane receptor that mediates avoidance response to dihydrocaffeic acid, a water-soluble repellent in Caenorhabditis elegans.

The ability to detect harmful chemicals rapidly is essential for the survival of all animals. In Caenorhabditis elegans (C. elegans), repellents trigger an avoidance response, causing animals to move away from repellents. Dihydrocaffeic acid (DHCA) is a water-soluble repellent and nonflavonoid catecholic compound that can be found in plant products. Using a Xenopus laevis (X. laevis) oocyte expression system, we identified a candidate dihydrocaffeic acid receptor (DCAR), DCAR-1. DCAR-1 is a novel seven-transmembrane protein that is expressed in the ASH avoidance sensory neurons of C. elegans. dcar-1 mutant animals are defective in avoidance response to DHCA, and cell-specific expression of dcar-1 in the ASH neurons of dcar-1 mutant animals rescued the defect in avoidance response to DHCA. Our findings identify DCAR-1 as the first seven-transmembrane receptor required for avoidance of a water-soluble repellent, DHCA, in C. elegans.

Aging: shall we take the high road?

For ectotherms, lifespan is increased at low temperature and decreased at high temperature. A new study in Caenorhabditis elegans shows that thermosensory neurons can counteract the effects of high temperature on lifespan by controlling the activity of a steroid signaling pathway.

Worm thermotaxis: a model system for analyzing thermosensation and neural plasticity.

Elucidation of the principal mechanism for sensory transduction, learning and memory is a fundamental question in neurobiology. The simple nervous system composed of only 302 neurons and the description of neural wiring combined with developed imaging techniques facilitate cellular and circuit level analysis of behavior in the nematode Caenorhabditis elegans. Recent comprehensive analysis of worm thermotaxis, an experience-modulated behavior, has begun to reveal molecular, cellular, and neural circuit basis of thermosensation and neural plasticity.

Maintenance of neuronal positions in organized ganglia by SAX-7, a Caenorhabditis elegans homologue of L1.

The L1 family of cell adhesion molecules is predominantly expressed in the nervous system. Mutations in human L1 cause neuronal diseases such as HSAS, MASA, and SPG1. Here we show that sax-7 gene encodes an L1 homologue in Caenorhabditis elegans. In sax-7 mutants, the organization of ganglia and positioning of neurons are abnormal in the adult stage, but these abnormalities are not observed in early larval stage. Misplacement of neurons in sax-7 mutants is triggered by mechanical force linked to body movement. Short and long forms of SAX-7 exhibited strong and weak homophilic adhesion activities in in vitro aggregation assay, respectively, which correlated with their different activities in vivo. SAX-7 was localized on plasma membranes of neurons in vivo. Expression of SAX-7 only in a single neuron in sax-7 mutants cell-autonomously restored its normal neuronal position. Expression of SAX-7 in two different head neurons in sax-7 mutants led to the forced attachment of these neurons. We propose that both homophilic and heterophilic interactions of SAX-7 are essential for maintenance of neuronal positions in organized ganglia.