TAK1 knockdown enhances lipopolysaccharide-induced secretion of proinflammatory cytokines in myeloid cells via unleashing MEKK3 activity

Nrf2 activation by neferine mitigates microglial neuroinflammation after subarachnoid hemorrhage through inhibiting TAK1-NF-κB signaling

Oxidative stress and neuroinflammation are two major causes leading to early brain injury after subarachnoid hemorrhage (SAH). Nuclear factor E2-related factor 2 (Nrf2) is a critical transcription factor that contributes to antioxidant responses. Additionally, Nrf2 could inhibit transforming growth factor beta-activated kinase 1 (TAK1), which plays a vital role in microglial activation-mediated neuroinflammation. Neferine (NE) exhibits considerable protective effects in diverse disease models. However, the detailed effect and mechanism of NE on SAH remain unknown. Our data showed that NE treatment significantly reduced behavior and cognitive impairment, and brain edema in the early period after SAH. In addition, NE mitigated SAH-induced oxidative damage, neuroinflammation, and neural death. Moreover, NE inhibited M1 microglial polarization and enhanced M2 phenotype microglia both in vivo and in vitro. Further investigations revealed that NE enhanced the Nrf2-antioxidant response element (ARE) signaling pathway and suppressed TAK1-NF-κB signaling. In contrast, depletion of Nrf2 by ML385 suppressed Nrf2-ARE signaling, induced TAK1-NF-κB activation, and further promoted M1 microglial polarization. Additionally, ML385 abated the neuroprotective effects of NE against SAH. Notably, LPS also aggravated TAK1-NF-κB activation and reversed the beneficial effects of NE after SAH. In summary, NE provides protection after SAH by inhibiting oxidative stress and modulating microglial polarization through Nrf2 activation and TAK1-NF-κB suppression.

Functional characterization of MEKK3 in the intestinal immune response to bacterial challenges in grass carp (Ctenopharyngodon idella)

Mitogen-activated protein kinase kinase kinase 3 (MEKK3) is an evolutionarily conserved Ser/Thr protein kinase of the MEKK family that is essential for the host immune response to pathogen challenges in mammals. However, the immune function of MEKK3s in lower vertebrate species, especially in bony fish, remains largely unknown. In this study, a fish MEKK3 (designated CiMEKK3) gene was cloned and identified from grass carp (Ctenopharyngodon idella). The present CiMEKK3 cDNA encoded a 620 amino acid polypeptide containing a conserved S-TKc domain and a typical PB1 domain. Several potential immune-related transcription factor-binding sites, including activating protein 1 (AP-1), nuclear factor kappa B (NF-κB) and signal transducer and activator of downstream transcription 3 (STAT3), were observed in the 5’ upstream DNA sequence of CiMEKK3. A phylogenetic tree showed that CiMEKK3 exhibits a close evolutionary relationship with MEKK3s from Cyprinus carpio and Carassius auratus. Quantitative real-time PCR analysis revealed that CiMEKK3 transcripts were widely distributed in all selected tissues of healthy grass carp, with a relatively high levels observed in the gill, head kidney and intestine. Upon in vitro challenge with bacterial pathogens (Aeromonas hydrophila and Aeromonas veronii) and pathogen-associated molecular patterns (PAMPs) (lipopolysaccharide (LPS), peptidoglycan (PGN), L-Ala-γ-D-Glu-mDAP (Tri-DAP) and muramyl dipeptide (MDP)), the expression levels of CiMEKK3 in the intestinal cells of grass carp were shown to be significantly upregulated in a time-dependent manner. In vivo injection experiments revealed that CiMEKK3 transcripts were significantly induced by MDP challenge in the intestine; however, these effects could be inhibited by the nutritional dipeptides carnosine and Ala-Gln. Moreover, subcellular localization analysis and luciferase reporter assays indicated that CiMEKK3 could act as a cytoplasmic signal-transducing activator involved in the regulation of NF-κB and MAPK/AP-1 signaling cascades in HEK293T cells. Taken together, these findings strongly suggest that CiMEKK3 plays vital roles in the intestinal immune response to bacterial challenges, which will aid in understanding the pathogenesis of inflammatory bowel disease in bony fish.

MEKK3 in hybrid snakehead (Channa maculate ♀ ×Channa argus ♂): Molecular characterization and immune response to infection with Nocardia seriolae and Aeromonas schubertii

Mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 3 (MEKK3) is a serine/threonine protein kinase that acts as a key regulator and is widely involved in various innate and acquired immune signaling pathways. In this study, we first cloned the complete open reading frame (ORF) of the MEKK3 gene (named CcMEKK3) in a hybrid snakehead (Channa maculate ♀ × Channa argus ♂). The full-length ORF of CcMEKK3 is 1851 bp, and encodes a putative protein of 616 amino acids containing a serine/threonine kinase catalytic (S-TKc) domain and a Phox and Bem1p (PB1) domain. A sequence alignment and phylogenetic tree analysis showed that CcMEKK3 is highly conserved relative to the MEKK3 proteins of other teleost species. CcMEKK3 was constitutively expressed in all the healthy hybrid snakehead tissues tested, with greatest expression in the immune tissues, such as the head kidney and spleen. The expression of CcMEKK3 was usually upregulated in the head kidney, spleen, and liver at different time points after infection with Nocardia seriolae or Aeromonas schubertii. Similarly, the dynamic expression levels of CcMEKK3 in head kidney leukocytes after stimulation revealed that CcMEKK3 was induced by LTA, LPS, and poly(I:C). In the subcellular localization analysis, CcMEKK3 was evenly distributed in the cytoplasm of HEK293T cells, and its overexpression significantly promoted the activities of NF-κB and AP-1. These results suggest that CcMEKK3 is involved in the immune defense against these two pathogens, and plays a crucial role in activating the NF-κB and MAPK signaling pathways.

Cerebral Cavernous Malformation Proteins in Barrier Maintenance and Regulation

Cerebral cavernous malformation (CCM) is a disease characterized by mulberry shaped clusters of dilated microvessels, primarily in the central nervous system. Such lesions can cause seizures, headaches, and stroke from brain bleeding. Loss-of-function germline and somatic mutations of a group of genes, called CCM genes, have been attributed to disease pathogenesis. In this review, we discuss the impact of CCM gene encoded proteins on cellular signaling, barrier function of endothelium and epithelium, and their contribution to CCM and potentially other diseases.

The interaction of TAK1 and TAB1 enhances LPS-induced cytokine release via modulating NF-κB activation (Larimichthys crocea)

Transforming growth factor-β-activating kinase 1 (TAK1) is triggered by foreign pathogenic infection and involves in proinflammatory response through the activation of nuclear factor-κB (NF-κB), which is specifically regulated by TAK1-binding protein 1 (TAB1). However, the expression and regulatory characterizations of TAK1 and TAB1 in fish immune response remain largely unknown. In the present study, the cDNA sequences of TAK1 (LcTAK1) and TAB1 (LcTAB1) were identified from large yellow croaker, Larimichthys crocea. The open reading frame (ORF) of LcTAK1 was 1725 bp in length, encoding 574 amino acids. The putative LcTAK1 protein contained a protein kinase domain and a C-terminal coiled-coil region. The ORF of LcTAB1 was 1518 bp encoding 505 amino acids. And a typical PP2Cc domain and a conserved sequence motif (PYVDFSQFYLLWGSDH) at C-terminal were identified in the predicted LcTAB1 protein. Multiple alignments showed that LcTAK1 shared 74.0-97.9% and LcTAB1 shared 37.4-95.8% sequence identities with TAK1 and TAB1 proteins from other species, respectively. Quantitative PCR analysis indicated that both LcTAK1 and LcTAB1 were broadly expressed in all examined tissues, with the most predominant expression in brain and the weakest expression in muscle, respectively. Subcellular localization revealed that both LcTAK1 and LcTAB1 expressed in the cytoplasm. In addition, LcTAK1 transcripts increased significantly in LCK cells after flagellin, LPS and poly I:C stimulation while LcTAB1 enhanced greatly after LPS and poly I:C challenge. Furthermore, the roles of them in NF-κB activation were investigated by overexpression of LcTAK1 and LcTAB1 in HEK293T cells. Our results revealed that NF-κB luciferase promoter expression could not be induced by overexpression of LcTAK1 or LcTAB1 alone, however, it could be induced by co-expression of LcTAK1 and LcTAB1 together. Moreover, the roles of LcTAK1 and LcTAB1 in immune response analysis showed that NF-κB activation enhanced significantly in co-overexpressed HEK293T cells following LPS and poly I:C stimulation. However, the expression levels of tumor necrosis factor (TNF)-α, Interleukin-6 (IL-6) and IL-8 were induced only after LPS challenge (p < .05). These findings suggested that the TAK1-TAB1 complex of large yellow croaker might play an important role in pro-inflammatory cytokines and chemokine release after LPS stimulation via inducing NF-κB activation.