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Review
. 2023 Jul 21:14:1168848.
doi: 10.3389/fimmu.2023.1168848. eCollection 2023.

HDAC6 inhibition: a significant potential regulator and therapeutic option to translate into clinical practice in renal transplantation

Affiliations
Review

HDAC6 inhibition: a significant potential regulator and therapeutic option to translate into clinical practice in renal transplantation

Qian-Qian Zhang et al. Front Immunol. .

Abstract

Histone deacetylase 6 (HDAC6), an almost exclusively cytoplasmic enzyme, plays an essential role in many biological processes and exerts its deacetylation-dependent/independent effects on a variety of target molecules, which has contributed to the flourishing growth of relatively isoform-specific enzyme inhibitors. Renal transplantation (RT) is one of the alternatively preferred treatments and the most cost-effective treatment approaches for the great majority of patients with end-stage renal disease (ESRD). HDAC6 expression and activity have recently been shown to be increased in kidney disease in a number of studies. To date, a substantial amount of validated studies has identified HDAC6 as a pivotal modulator of innate and adaptive immunity, and HDAC6 inhibitors (HDAC6i) are being developed and investigated for use in arrays of immune-related diseases, making HDAC6i a promising therapeutic candidate for the management of a variety of renal diseases. Based on accumulating evidence, HDAC6i markedly open up new avenues for therapeutic intervention to protect against oxidative stress-induced damage, tip the balance in favor of the generation of tolerance-related immune cells, and attenuate fibrosis by inhibiting multiple activations of cell profibrotic signaling pathways. Taken together, we have a point of view that targeting HDAC6 may be a novel approach for the therapeutic strategy of RT-related complications, including consequences of ischemia-reperfusion injury, induction of immune tolerance in transplantation, equilibrium of rejection, and improvement of chronic renal graft interstitial fibrosis after transplantation in patients. Herein, we will elaborate on the unique function of HDAC6, which focuses on therapeutical mechanism of action related to immunological events with a general account of the tantalizing potential to the clinic.

Keywords: HDAC6; ameliorate outcomes; epigenetics; immunoregulation; molecular regulation; renal transplantation; selective HDAC6 inhibitors.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Schematic depiction of the different isoforms of HDAC. N, N-terminus; C, C-terminus; Blue lines depict the length of the protein; Yellow bars depict catalytic domains; Orange bars depict nuclear localization sequences (NLS); Brown bars depict nuclear export sequences (NES1, NES2); Green bar depicts Ser-Glu containing a tetradecapeptide repeating domain (SE14); Purple bar depicts a zinc-finger ubiquitin-binding domain (ZnF-UBD).
Figure 2
Figure 2
Description of HDAC6 on IRI pathways. IRI causes immune cells of both the innate and adaptive immune systems, such as neutrophils, DCs, macrophages, and lymphocyte subsets contribute to the pathogenesis and pathological processes of IRI. IRI-generated ROS promotes activation of the NF-κB and AP-1 signaling pathways with subsequent transcription and production of inflammatory cytokines signaling mechanisms and transcriptional regulatory pathways. HDAC6 deacetylate histone and non-histone proteins, which blockage-elicited renal protection is associated with inhibition of suppression of inflammatory responses, and reduction of oxidative stress. HDAC6 inhibitions dampen the expression of ROS with subsequent transcription and production of proinflammatory cytokines by inhibiting the NF-κB and AP-1 signaling pathways.
Figure 3
Figure 3
Mechanisms of graft tolerance (A) and rejection (B) consist of complex processes involving the induction of proinflammatory APCs and tolerogenic DCs, leading to a different microenvironment. (1) HDAC6 promotes the expression of T-bet in the Th1 master regulating the ratio of Th1 to Th2, which also controls the population of CD4 cells, and the CD4T-bet/CD4T-GATA-3 ratio was significantly reduced in the HDAC6i group. in the HDAC6i group. (2) Acetylation promotes Foxp3 dimerisation, DNA binding and transcriptional activity, and expansion of the Treg population, and is ultimately associated with immune tolerance. The effects are likely to be related to increased Foxp3 acetylation and consequent expansion of Tregs. (3) HDAC6 inhibitor upregulates the Treg cell population through the STAT3/IL-10 tolerogenic axis to overcome immune tolerance and tilt the balance towards T-cell immunity. HDAC6 improved the expression levels of TF Rora in Th17, IL-17A secretion in Th17 cells and IL-4 levels secreted by Tregs, Th2 induced, as well as the differentiation of TH17/Treg imbalance. HDAC6i has therapeutic effects on the pathology of acute rejection by targeting the HDAC6/HIF-1a/ROR gt/Th17 signalling axis.
Figure 4
Figure 4
Schematic illustration of the anti-fibrotic property of HDAC6i in renal transplantation. Injured tissue or activated immune cells secrete profibrotic factors that induce fibroblast differentiation into myofibroblasts. Myofibroblasts actively synthesise extracellular matrix. HDAC6i negatively regulates fibrosis. (1) In the initial stage of the pro-fibrotic process, intra-graft inflammation, an integral part of the host defence mechanism in response to injury, is activated. Through modulation of p38 MAPK, NF-kB and AP-1 pathways, several pro-inflammatory, pro-fibrotic cytokines and adhesion molecules (MMP-1, MMP-2, MMP-9, MCP-1) are secreted by tubular cells with consequent recruitment of inflammatory infiltrates (lymphocytes, macrophages, DCs, neutrophils) that may facilitate the recruitment of new interstitial mononuclear cells. (2) Macrophages are a major source of TGF-b, which modulates the production of IL-1β, TNF-α, IFN-bγ and IL-10 and induces myofibroblast differentiation and the production of ECM proteins. (3) Damaged mitochondria mediate apoptosis and necrosis with the consequent release of DAMPs, which activate the NLRP3 inflammasome and participate in the prosis of fibrosis. (4) ROS accumulation via IRI, NADPH oxidase and mitochondrial dysfunction contribute to EMT. (5) Inhibition of HDAC6 attenuated EGFR, TGF-b1 induced EMT markers, which is accompanied by HDAC6-dependent deacetylation of a -tubulin. (6) The underlying mechanism by which HDAC6 inhibition can attenuate fibrosis by inhibiting profibrotic genes, multiple activations of cell pro-fibrotic signalling pathways and inflammation. Dashed arrows indicate indirect pro-fibrotic effects.

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Grants and funding

This work was supported by research grants from National Natural Science Foundation of China (No. 81873511).