TonEBP regulates the hyperosmotic expression of aquaporin 1 and 5 in the intervertebral disc

Electroacupuncture attenuates intervertebral disc degeneration by upregulating aquaporins via the cAMP/PKA pathway

BACKGROUND

Intervertebral disc degeneration (IVDD) is characterized by a decrease in extracellular matrix (ECM) and water loss, which is a major cause of low back pain (LBP). Electroacupuncture (EA) has long been used to relieve LBP in IVDD. To investigate whether EA can upregulate aquaporins (AQPs) in IVDD via the cAMP/PKA pathway in a rabbit model of disc degeneration.

METHODS

A homemade loading device was adapted to trigger a disc degeneration model. After 28 days, EA treatment was performed. Magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), and diffusion tensor imaging (DTI) were performed to evaluate AQP content and water diffusion. AQP protein expression in the slices was observed by Western blot and immunofluorescence (IF) staining. The pathology of the intervertebral discs was determined by staining. cAMP and PKA levels were examined using ELISA, and the expression of AQP genes as well as the cAMP/PKA pathway and its related molecules were examined using quantitative reverse transcription-PCR (qRT-PCR) and Western blot analysis.

RESULTS

The EA intervention reduced MRI Pfirrmann scores, fractional anisotropy (FA), and apparent diffusion coefficient (ADC) values. EA can upregulate the expression of AQP1 and AQP3, thereby improving the pathological morphology of the nucleus pulposus (NP) and the cartilage endplate of the intervertebral disc. cAMP and PKA levels were significantly increased after EA intervention in rabbits with IVDD. EA intervention can partially improve the expression of related molecules in the cAMP/PKA pathway, but H-89 reverses the effect of EA.

CONCLUSION

EA can attenuate intervertebral disc degeneration by regulating AQP expression, a process that may be mediated by the cAMP/PKA pathway.

Ex Vivo and In Vitro Proteomic Approach to Elucidate the Relevance of IL-4 and IL-10 in Intervertebral Disc Pathophysiology

Background

This study investigates the native presence and potential anabolic effects of interleukin (IL)-4 and IL-10 in the human intervertebral disc (IVD).

Methods

Human nucleus pulposus (NP) cells cultured in 3D from trauma and degenerate IVDs and NP explants were stimulated with 10 ng/mL IL-4, IL-10, or each in combination with 1 ng/mL IL-1β stimulation. The role of IL-4 and IL-10 in the IVD was evaluated using immunohistochemistry, gene expression, and Luminex multiplex immunoassay proteomics (73 secreted) and phosphoproteomics (21 phosphorylated proteins).

Results

IL-4, IL-4R, and IL-10R expression and localization in human cartilage endplate tissue were demonstrated for the first time. No significant gene expression changes were noted under IL-4 or IL-10 stimulation. However, IL-1β stimulation significantly increased MMP3, COX2, TIMP1, and TRPV4 expression in NP cells from trauma IVDs. Combined IL-4 and IL-1β treatment induced a significant increase in protein secretion of IL-1α, IL-7, IL-16, IL-17F, IL-18, IFNγ, TNF, ST2, PROK1, bFGF2, and stem cell factor exclusively in NP cells from degenerated IVDs. Conversely, the secretome profile of explants revealed an IL-4-mediated decrease in CXCL13 following treatment with IL-1β. Combined IL-10 and IL-1β treatment increased neurotrophic growth factor secretion compared with IL-10 baseline.

Conclusions

The NP cell phenotype affects the pleiotropic role of IL-4, which can induce a pro-inflammatory response in the presence of catabolic stimuli and enhance the effects of IL-1β in degenerated IVDs. Environmental factors, including 3D culture and hypoxia, may alter IL-4's role. Finally, IL-10's potential neurotrophic effects under catabolic stimuli warrant further investigation to clarify its role in IVD degeneration.

PCRX-201, a novel IL-1Ra gene therapy treatment approach for low back pain resulting from intervertebral disc degeneration

Low back pain is the leading cause of global disability with intervertebral disc (IVD) degeneration a major cause. However, no current treatments target the underlying pathophysiological causes. PCRX-201 presents a novel gene therapy approach that addresses this issue. PCRX-201 codes for interleukin-1 receptor antagonist, the signalling inhibitor of the pro-inflammatory cytokine interleukin-1, which orchestrates the catabolic degeneration of the IVD. Here, the ability of PCRX-201 to transduce human nucleus pulposus cells to increase IL-1Ra production was assessed together with effects on catabolic pathways. When transduced with PCRX-201, the production and release of IL-1Ra was increased in degenerate human nucleus pulposus cells and tissue. Whereas, the production of downstream proteins, including IL-1β, IL-6, MMP3, ADAMTS4 and VEGF were decreased in both cells and tissue, indicating a reduction in IL-1-induced catabolic signalling. Here, a novel gene therapy vector, PCRX-201, was shown to transduce degenerate NP cells and tissue, increasing the production of IL-1Ra. The increased IL-1Ra resulted in decreased production of catabolic cytokines, enzymes and angiogenic factors, whilst also increasing aggrecan expression. This demonstrates PCRX-201 enables the inhibition of IL-1-driven IVD degeneration. The ability of PCRX-201 to elicit anti-catabolic responses is promising and warrants further development to determine the efficacy of this exciting, novel gene therapy.

Exploring the correlation between magnetic resonance diffusion tensor imaging (DTI) parameters and aquaporin expression and biochemical composition content in degenerative intervertebral disc nucleus pulposus tissue: a clinical experimental study

OBJECTIVE

This study investigates the correlation between magnetic resonance diffusion tensor imaging (DTI) parameters and biochemical composition in degenerative intervertebral disc nucleus pulposus tissue, offering a potential reference for the clinical diagnosis and efficacy evaluation of intervertebral disc degeneration.

METHODS

Human lumbar intervertebral disc nucleus pulposus tissue samples were collected via full endoscopic minimally invasive surgery. DTI was employed to quantitatively measure fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values in the degenerative nucleus pulposus, examining the relationship between Pfirrmann grading and these DTI parameters. Western blotting was used to detect the expression levels of aquaporin 1 (AQP1) and aquaporin 3 (AQP3) in the degenerative tissue. The glycosaminoglycan (GAG) content was quantified using the dimethylmethylene blue (DMMB) colorimetric assay, and collagen content was assessed with the Sircol soluble collagen assay kit. The relationship between Pfirrmann grading and biochemical composition was also analyzed. Finally, correlation analysis was performed between the FA and ADC values from the human nucleus pulposus tissue and their GAG and collagen contents.

RESULTS

A total of 39 patients (19 males, 20 females) with lumbar disc herniation (LDH), averaging 54.41 years of age, were included. As the degree of Pfirrmann degeneration increased, FA values rose, while ADC values continuously declined. Concurrently, as degeneration progressed, expression of AQP1 and AQP3 proteins decreased, GAG content significantly diminished, and collagen content increased. FA values exhibited a moderate negative correlation with GAG content (r = -0.5974, P < 0.0001) and a strong positive correlation with collagen content (r = 0.8694, P < 0.0001). ADC values showed a moderate positive correlation with GAG content (r = 0.6873, P < 0.0001) and a strong negative correlation with collagen content (r = -0.8502, P < 0.0001).

CONCLUSION

The FA and ADC values derived from magnetic resonance DTI, along with the protein expression levels of AQPs, can reflect the severity of intervertebral disc degeneration to a certain extent. Additionally, the content of glycosaminoglycans and collagen in the nucleus pulposus of the intervertebral disc correlates with the FA and ADC values of the DTI parameters. Therefore, magnetic resonance DTI quantitative imaging provides a means to assess the biochemical composition changes within the intervertebral discs, offering valuable insights for the clinical diagnosis and evaluation of therapeutic efficacy in intervertebral disc degenerative diseases.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR2000041151, Registered on 19 December, 2020, https://www.chictr.org.cn/showproj.html?proj=206119 .

Predicting proximal tubule failed repair drivers through regularized regression analysis of single cell multiomic sequencing

Renal proximal tubule epithelial cells have considerable intrinsic repair capacity following injury. However, a fraction of injured proximal tubule cells fails to undergo normal repair and assumes a proinflammatory and profibrotic phenotype that may promote fibrosis and chronic kidney disease. The healthy to failed repair change is marked by cell state-specific transcriptomic and epigenomic changes. Single nucleus joint RNA- and ATAC-seq sequencing offers an opportunity to study the gene regulatory networks underpinning these changes in order to identify key regulatory drivers. We develop a regularized regression approach to construct genome-wide parametric gene regulatory networks using multiomic datasets. We generate a single nucleus multiomic dataset from seven adult human kidney samples and apply our method to study drivers of a failed injury response associated with kidney disease. We demonstrate that our approach is a highly effective tool for predicting key cis- and trans-regulatory elements underpinning the healthy to failed repair transition and use it to identify NFAT5 as a driver of the maladaptive proximal tubule state.

Achilles' Heel-The Significance of Maintaining Microenvironmental Homeostasis in the Nucleus Pulposus for Intervertebral Discs

The dysregulation of intracellular and extracellular environments as well as the aberrant expression of ion channels on the cell membrane are intricately linked to a diverse array of degenerative disorders, including intervertebral disc degeneration. This condition is a significant contributor to low back pain, which poses a substantial burden on both personal quality of life and societal economics. Changes in the number and function of ion channels can disrupt the water and ion balance both inside and outside cells, thereby impacting the physiological functions of tissues and organs. Therefore, maintaining ion homeostasis and stable expression of ion channels within the cellular microenvironment may prove beneficial in the treatment of disc degeneration. Aquaporin (AQP), calcium ion channels, and acid-sensitive ion channels (ASIC) play crucial roles in regulating water, calcium ions, and hydrogen ions levels. These channels have significant effects on physiological and pathological processes such as cellular aging, inflammatory response, stromal decomposition, endoplasmic reticulum stress, and accumulation of cell metabolites. Additionally, Piezo 1, transient receptor potential vanilloid type 4 (TRPV4), tension response enhancer binding protein (TonEBP), potassium ions, zinc ions, and tungsten all play a role in the process of intervertebral disc degeneration. This review endeavors to elucidate alterations in the microenvironment of the nucleus pulposus during intervertebral disc degeneration (IVDD), with a view to offer novel insights and approaches for exploring therapeutic interventions against disc degeneration.

The role of the osmosensitive transcription factor NFAT5 in corneal edema resorption after injury

The osmosensitive transcription factor nuclear factor of activated T cells 5 (NFAT5; or tonicity-responsive enhancer binding protein; TonEBP) plays a key role in macrophage-driven regulation of cutaneous salt and water balance. In the immune-privileged and transparent cornea, disturbances in fluid balance and pathological edema result in corneal transparency loss, which is one of the main causes of blindness worldwide. The role of NFAT5 in the cornea has not yet been investigated. We analyzed the expression and function of NFAT5 in naive corneas and in an established mouse model of perforating corneal injury (PCI), which causes acute corneal edema and transparency loss. In uninjured corneas, NFAT5 was mainly expressed in corneal fibroblasts. In contrast, after PCI, NFAT5 expression was highly upregulated in recruited corneal macrophages. NFAT5 deficiency did not alter corneal thickness in steady state; however, loss of NFAT5 led to accelerated resorption of corneal edema after PCI. Mechanistically, we found that myeloid cell-derived NFAT5 is crucial for controlling corneal edema, as edema resorption after PCI was significantly enhanced in mice with conditional loss of NFAT5 in the myeloid cell lineage, presumably due to increased pinocytosis of corneal macrophages. Collectively, we uncovered a suppressive role for NFAT5 in corneal edema resorption, thereby identifying a novel therapeutic target to combat edema-induced corneal blindness.

Cartilage extracellular matrix-derived matrikines in osteoarthritis

Osteoarthritis (OA) is among the most frequent diseases of the musculoskeletal system. Degradation of cartilage extracellular matrix (ECM) is a hallmark of OA. During the degradation process, intact/full-length proteins and proteolytic fragments are released which then might induce different downstream responses via diverse receptors, therefore leading to different biological consequences. Collagen type II and the proteoglycan aggrecan are the most abundant components of the cartilage ECM. However, over the last decades, a large number of minor components have been identified and for some of those, a role in the manifold processes associated with OA has already been demonstrated. To date, there is still no therapy able to halt or cure OA. A better understanding of the matrikine landscape occurring with or even preceding obvious degenerative changes in joint tissues is needed and might help to identify molecules that could serve as biomarkers, druggable targets, or even be blueprints for disease modifying drug OA drugs. For this narrative review, we screened PubMed for relevant literature in the English language and summarized the current knowledge regarding the function of selected ECM molecules and the derived matrikines in the context of cartilage and OA.

Aquaporin-5 Dynamic Regulation

Aquaporin-5 (AQP5), belonging to the aquaporins (AQPs) family of transmembrane water channels, facilitates osmotically driven water flux across biological membranes and the movement of hydrogen peroxide and CO₂. Various mechanisms have been shown to dynamically regulate AQP5 expression, trafficking, and function. Besides fulfilling its primary water permeability function, AQP5 has been shown to regulate downstream effectors playing roles in various cellular processes. This review provides a comprehensive overview of the current knowledge of the upstream and downstream effectors of AQP5 to gain an in-depth understanding of the physiological and pathophysiological processes involving AQP5.