Biology subjects

Kim, M. K. M.

Publications and source records attributed to Kim, M. K. M..

3 recordsLinked to original sources

bioRxiv2026

Regulation of Nucleus Pulposus Cell Phenotype Through RhoA Signaling and Microenvironment

Intervertebral disc degeneration is associated with loss of nucleus pulposus (NP) cell phenotype and extracellular matrix, both processes linked to changes in cytoskeletal contractility and cell shape. Here, we tested whether microenvironment-specific modulation of RhoA signaling can restore NP-like morphology and gene expression in NP cells cultured in 2D and in 3D alginate. In 2D monolayer culture, where cells are spread and mechanically activated, pharmacologic inhibition of RhoA with CT04 reduced RhoA activity, decreased actomyosin contractility gene expression, and shifted morphology toward a smaller, more circular phenotype. Bulk RNA sequencing showed that CT04 treatment increased expression of NP phenotypic and matrix-related genes including ACAN, GDF5, CHST3, and MUSTN1 while decreasing expression of catabolic and fibroblast-associated genes including ADAMTS1/9 and COL1, consistent with enrichment of extracellular matrix pathways. In contrast, RhoA activation with CN03 in 2D culture increased actin and phosphorylated myosin light chain intensity but produced limited phenotypic improvement. In 3D alginate, which minimizes integrin-mediated adhesion, baseline actomyosin markers were reduced relative to 2D culture. In alginate, RhoA activation with CN03 increased the amount of actin, phosphorylated myosin light chain, and actomyosin gene expression, yet also promoted a more compact, circular morphology and increased NP markers, including ACAN and KRT19 with repeated dosing. Across culture conditions, increased cell roundness was consistently associated with increased ACAN expression, indicating strong coupling between cytoskeletal state, morphology, and NP matrix programs. Together, these findings demonstrate that RhoA pathway perturbation can promote NP phenotypic gene expression in both 2D and 3D culture, but the direction of optimal modulation depends on the microenvironment, supporting RhoA signaling as a context-dependent therapeutic target for disc regeneration.

cell biology↗

bioRxiv2024

HMGB1 mediates macrophage recruitment and regional intervertebral disc tissue functional and mechanical property changes following injury.

ObjectiveFrequently evaluated in musculoskeletal disease, damage associated molecular patterns (DAMPs) respond to tissue damage and cellular stress by facilitating an inflammatory response via macrophage activation and broad inflammatory pathway activation. In the context of disc degeneration (DD), high mobility group box 1 (HMGB1), a potent intracellular DAMP, is seen to be increased within severely degenerated human IVDs and to directly mediate inflammatory responses within disc cells in vitro. To further understand how HMGB1 mediated inflammation influences DD, this study evaluated the possible protective effect of an HMGB1 knockout on DD pathology following injury. MethodsUsing a needle puncture injury model in murine caudal IVDs we evaluated DD pathology within an IVD specific Hmgb1 knockout (KO) model. Structural and compositional changes in IVD cellularity, histopathology, disc height, and biomechanics were evaluated in addition to an assessment of disc inflammation via gene expression and macrophage presence throughout the course of degeneration. ResultsHMGB1 expression robustly increased shortly following needle puncture injury and elevated levels were sustained up to 28-days post injury both in injured IVDs and in the IVDs adjacent to the level of injury. IVD specific Hmgb1 KO mice had an increased disc height following injury both at the injured and adjacent to injury level compared to injured WT IVDs. Hmgb1 KO also protected against tissue mechanical property losses at both the injured (dynamic modulus) and adjacent to injury level (dynamic modulus, creep, and equilibrium modulus) compared to injured WT IVDs, however there was no significant effect on histopathologic scores post injury. Hmgb1 KO resulted in alterations in macrophage (F4/80+) recruitment to the IVD post injury in vivo. A lower macrophage migration was also observed in vitro in response to the secretome of an injured Hmgb1 KO IVD compared to injured WT IVDs. Hmgb1 KO had no effect on inflammatory gene expression changes following injury within adjacent to injury level or injury level IVDs. ConclusionOverall findings indicate that HMGB1 is upregulated regionally, at both the injured level and at the level adjacent to injury. Results suggest that HMGB1 plays a role in mediating structural, biomechanical, and inflammatory responses to IVD injury and serves as a potent chemoattractant, mediating macrophage recruitment to the IVD and overall migratory function.

bioengineering↗

bioRxiv2023

Nuclear Factor Kappa B Over-Activation in the Intervertebral Disc Leads to Macrophage Recruitment and Severe Disc Degeneration

ObjectiveLow back pain (LBP) is the leading cause of global disability and is thought to be driven primarily by intervertebral disc (IVD) degeneration (DD). Persistent upregulation of catabolic enzymes and inflammatory mediators have been associated with severe cases of DD. Nuclear factor kappa B (NF-{kappa}B) is a master transcription regulator of immune responses and is over expressed during inflammatory-driven musculoskeletal diseases, including DD. However, its role in triggering DD is unknown. Therefore, this study investigated the effect of NF-{kappa}B pathway over-activation on IVD integrity and DD pathology. MethodsUsing skeletally mature mouse model, we genetically targeted IVD cells for canonical NF-{kappa}B pathway activation via expression of a constitutively active form of inhibitor of {kappa}B kinase B (IKK{beta}), and assessed changes in IVD cellularity, structural integrity including histology, disc height, and extracellular matrix (ECM) biochemistry, biomechanics, expression of inflammatory, catabolic, and neurotropic mediators, and changes in macrophage subsets, longitudinally up to 6-months post activation. ResultsProlonged NF-{kappa}B activation led to severe structural degeneration, with a loss of glycosaminoglycan (GAG) content and complete loss of nucleus pulposus (NP) cellularity. Structural and compositional changes decreased IVD height and compressive mechanical properties with prolonged NF-{kappa}B activation. These alterations were accompanied by increases in gene expression of inflammatory molecules (Il1b, Il6, Nos2), chemokines (Mcp1, Mif), catabolic enzymes (Mmp3, Mmp9, Adamts4), and neurotrophic factors (Bdnf, Ngf) within IVD tissue. Increased recruitment of activated F4/80+ macrophages exhibited a greater abundance of pro-inflammatory (CD38+) over inflammatory-resolving (CD206+) macrophage subsets in the IVD, with temporal changes in the relative abundance of macrophage subsets over time, providing evidence for temporal regulation of macrophage polarization in DD in vivo, where macrophages participate in resolving the inflammatory cascade but promote fibrotic transformation of the IVD matrix. We further show that NF-{kappa}B driven secretory factors from IVD cells increase macrophage migration and inflammatory activation, and that the secretome of inflammatory-resolving macrophages mitigates effects of NF-{kappa}B overactivation. ConclusionOverall the observed results suggest prolonged NF-{kappa}B activation can induce severe DD, acting through increases in inflammatory cytokines, chemotactic proteins, catabolic enzymes, and the recruitment and inflammatory activation of a macrophage cell populations, that can be mitigated with inflammatory-resolving macrophage secretome.

bioengineering↗