Biology subjects

Chung, M.-K.

Publications and source records attributed to Chung, M.-K..

5 recordsLinked to original sources

bioRxiv2025

Multiscale 3D whole joint cellular and molecular mapping dissects the relationship between structure and pain

Understanding musculoskeletal joints from a 3D multiscale perspective, from molecular to anatomical levels, is essential for resolving the confounding relationships between structure and pain, elucidating the intricate mechanisms regulating joint health and diseases, and developing new treatment strategies. Here, we introduce a musculoskeletal joint immunostaining and clearing (MUSIC) method specifically designed to overcome key challenges of immunostaining and optical clearing of intact joints. Coupled with large-field light sheet microscopy, our approach enables 3D high-resolution, microscale neurovascular mapping within the context of whole-joint anatomy without the need for image coregistration across various joints, including temporomandibular joints, knees, and spines, and multiple species, including mouse, rat, and pig. Our findings reveal 3D heterogeneous distributions of neurovascular networks and previously uncharacterized neurovascular pathways within joints. Using the proteoglycan 4 knockout (Prg4-/-) mouse model of joint degeneration, we identified significant alterations in joint-wide neurovascular architecture, highlighting neurovascular changes along degenerative processes. Furthermore, in a traumatic joint injury mouse model, we observed long-lasting pain behavior and a time-course 3D neurovascular remodeling preceding detectable joint morphological change, bridging microscale alterations with potential pain mechanisms. This platform offers a powerful tool for multiscale 3D analysis, enabling new insights into joint pathophysiology and intricate interplay among joint tissues.

bioengineering↗

bioRxiv2024

Forced mouth opening induces post-traumatic hyperalgesia and associated peripheral sensitization after temporomandibular joints injury in mice

Temporomandibular disorder (TMD) is the most prevalent painful condition in the craniofacial area. The pathophysiology of TMD is not fully understood, and it is necessary to understand pathophysiology underlying painful TMD conditions to develop more effective treatment methods. Recent studies suggested that external or intrinsic trauma to TMJ is associated with chronic TMD in patients. Here, we investigated the effects of the TMJ trauma through forced-mouth opening (FMO) in mice to determine pain behaviors and peripheral sensitization of trigeminal nociceptors. FMO increased mechanical hyperalgesia assessed by von Frey test, spontaneous pain-like behaviors assessed by mouse grimace scale, and anxiety-like behaviors assessed by open-field test. In vivo GCaMP Ca2+ imaging of intact trigeminal ganglia (TG) showed increased spontaneous Ca2+ activity and mechanical hypersensitivity of TG neurons in the FMO compared to the sham group. Ca2+ responses evoked by cold, heat, and capsaicin stimuli were also increased. FMO-induced hyperalgesia and neuronal hyperactivities were not sex dependent. TG neurons sensitized following FMO were primarily small to medium-sized nociceptive afferents. Consistently, most TMJ afferents in the TG were small-sized peptidergic neurons expressing calcitonin gene-related peptides, whereas nonpeptidergic TMJ afferents were relatively low. FMO-induced intraneural inflammation in the surrounding tissues of the TMJ indicates potentially novel mechanisms of peripheral sensitization following TMJ injury. These results suggest that the TMJ injury leads to persistent post-traumatic hyperalgesia associated with peripheral sensitization of trigeminal nociceptors.

neuroscience↗

bioRxiv2024

Elucidation of neuronal activity in mouse models of TMJ injury by in vivo GCaMP Ca2+ imaging of intact trigeminal ganglion neurons

Patients with temporomandibular disorders (TMD) typically experience facial pain and discomfort or tenderness in the temporomandibular joint (TMJ), causing disability in daily life. Unfortunately, existing treatments for TMD are not always effective, creating a need for more advanced, mechanism-based therapies. In this study, we used in vivo GCaMP3 Ca2+ imaging of intact trigeminal ganglia (TG) to characterize functional activity of the TG neurons in vivo, specifically in TMJ animal models. This system allows us to observe neuronal activity in intact anatomical, physiological, and clinical conditions and to assess neuronal function and response to various stimuli. We observed a significant increase in spontaneously and transiently activated neurons responding to mechanical, thermal, and chemical stimuli in the TG of forced mouth open (FMO) mice. An inhibitor of the CGRP receptor significantly attenuated FMO-induced facial hypersensitivity. In addition, we confirmed the attenuating effect of CGRP antagonist on FMO-induced sensitization by in vivo GCaMP3 Ca2+ imaging of intact TG. Our results contribute to unraveling the role and activity of TG neurons in the TMJ pain animal models of TMD, bringing us closer understanding the pathophysiological processes underlying TMD. Our study also illustrates the utility of in vivo GCaMP3 Ca2+ imaging of intact TG for studies aimed at developing more targeted and effective treatments for TMD.

neuroscience↗

bioRxiv2023

ACTIVATION OF CYCLIN-DEPENDENT KINASE 5 BROADENS ACTION POTENTIALS IN HUMAN SENSORY NEURONS

Chronic pain is one of the most devastating and unpleasant conditions, associated with many pathological conditions. Tissue or nerve injuries induce comprehensive neurobiological plasticity in nociceptive neurons, which leads to chronic pain. Recent studies suggest that cyclin-dependent kinase 5 (CDK5) in primary afferents is a key neuronal kinase that modulates nociception through phosphorylation-dependent manner under pathological conditions. However, the impact of the CDK5 on nociceptor activity especially in human sensory neurons are not known. To determine the CDK5-mediated regulation of human dorsal root ganglia (hDRG) neuronal properties, we have performed the whole-cell patch clamp recordings in neurons dissociated from hDRG. CDK5 activation induced by overexpression of p35 depolarized the resting membrane potential and reduced the rheobase currents as compared to the uninfected neurons. CDK5 activation evidently changed the shape of the action potential (AP) by increasing AP rise time, AP fall time, and AP half width. The application of a prostaglandin E2 (PG) and bradykinin (BK) cocktail in uninfected hDRG neurons induced the depolarization of RMP and the reduction of rheobase currents along with increased AP rise time. However, PG and BK applications failed to induce any further significant changes in addition to the aforementioned changes of the membrane properties and AP parameters in the p35-overexpressing group. We conclude that CDK5 activation through the overexpression of p35 in dissociated hDRG neurons broadens AP in hDRG neurons and that CDK5 may play important roles in the modulation of AP properties in human primary afferents under pathological conditions, contributing to chronic pain.

neuroscience↗

bioRxiv2023

Mouse Homolog of Human IRF8G388S Mutation Provides Novel Insight into Osteoclastogenesis and Tooth Root Resorption

Previously, we reported a novel mutation in the Interferon Regulatory Factor 8 (IRF8) gene associated with multiple idiopathic cervical root resorption (MICRR), an aggressive form of tooth root resorption mediated by increased osteoclast activity. The IRF8 G388S variant in the highly conserved C-terminal motif is predicted to alter the protein structure, likely impairing IRF8 function. To investigate the molecular basis of MICRR and IRF8 function, we generated Irf8 knock-in (KI) mice using CRISPR/Cas9 modeling the human IRF8G388S mutation. The heterozygous (Het) and homozygous (Homo) Irf8 KI mice showed no gross morphological defects, and the development of hematopoietic cells was unaffected and similar to that in wild-type (WT) mice. The Irf8 KI Het and Homo mice showed no difference in macrophage gene signatures important for antimicrobial defenses and inflammatory cytokine production. Consistent with the phenotype observed in MICRR patients, Irf8 KI Het and Homo mice demonstrated significantly increased osteoclast formation and resorption activity in vivo and in vitro when compared to WT mice. The oral ligature inserted Irf8 KI Het and Homo mice displayed increased osteoclast-mediated alveolar bone loss and tooth root resorption compared to WT mice. The increased osteoclastogenesis noted in KI mice is due to the inability of mutant Irf8 G388S isoform to negatively inhibit NFATc1-dependent transcriptional activation and downstream osteoclast specific transcripts. This translational study delineates the IRF8 domain important for osteoclast function and provides novel insights into the IRF8 mutation associated with MICRR. Irf8G388S mutation mainly affects osteoclastogenesis while sparing immune cell development and function. The Irf8 KI mice serve as a novel translational model for studying the etiopathology of MICRR and developing targeted therapies for MICRR and other skeletal disorders mediated by increased osteoclast activity.

genetics↗