Lo Cascio et al. identified quisinostat as a potent second-generation HDAC inhibitor that penetrates the blood-brain barrier and sensitizes GBM tumors to radiation therapy. The cover image shows an artistic interpretation of how quisinostat treatment increases histone acetylation and relaxation of the chromatin. Quisinostat induces DNA damage and further synergizes with radiation to sensitize GBM cells. Combinatorial treatment with quisinostat and radiation can lead cells to two fates: cell death or the adoption of a neuronal-like cell fate. Image credit: Costanza Lo Cascio, Michael Gallagher, and Shwetal Mehta.
Hyperuricemia is implicated in numerous pathologies but the mechanisms underlying uric acid production are poorly understood. Using a combination of mouse studies, cultured cell studies, and human serum samples, we sought to determine the cellular source of uric acid. In mice, fasting and glucocorticoid treatment increased serum uric acid and uric acid release from ex vivo incubated skeletal muscle. In vitro, glucocorticoids and the transcription factor FoxO3 increased purine nucleotide degradation and purine release from differentiated muscle cells, which coincided with the transcriptional upregulation of AMP deaminase 3, a rate-limiting enzyme in adenine nucleotide degradation. Heavy isotope tracing during co-culture experiments revealed that oxidation of muscle purines to uric acid required their transfer from muscle cells to a cell type that expresses xanthine oxidoreductase, such as endothelial cells. Lastly, in healthy women, matched for age and body composition, serum uric acid was greater in individuals scoring below average on standard physical function assessments. Together, these studies reveal skeletal muscle purine degradation is an underlying driver of uric acid production, with the final step of uric acid production occurring primarily in a non-muscle cell type. This suggests that skeletal muscle fiber purine degradation may represent a therapeutic target to reduce serum uric acid and treat numerous pathologies.
Spencer G. Miller, Catalina Matias, Paul S. Hafen, Andrew S. Law, Carol A. Witczak, Jeffrey J. Brault
Circadian rhythm dysfunction is a hallmark of Parkinson Disease (PD), and diminished expression of the core clock gene Bmal1 has been described in PD patients. BMAL1 is required for core circadian clock function, but also serves non-rhythmic functions. Germline Bmal1 deletion can cause brain oxidative stress and synapse loss in mice, and can exacerbate dopaminergic neurodegeneration in response to the toxin MPTP. Here we examined the impact of cell type-specific Bmal1 deletion on dopaminergic neuron viability in vivo. We observed that global, post-natal deletion of Bmal1 caused spontaneous loss of tyrosine hydroxylase-positive (TH+) dopaminergic neurons in the substantia nigra pars compacta (SNpc). This was not replicated by light-induced disruption of behavioral circadian rhythms, and was not induced by astrocyte- or microglia-specific Bmal1 deletion. However, either pan-neuronal or TH neuron-specific Bmal1 deletion caused cell-autonomous loss of TH+ neurons in the SNpc. Bmal1 deletion did not change the percentage of TH neuron loss after alpha-synuclein fibril injection, though Bmal1 KO mice had fewer TH neurons at baseline. Transcriptomic analysis revealed dysregulation of pathways involved in oxidative phosphorylation and Parkinson Disease. These findings demonstrate a cell-autonomous role for BMAL1 in regulating dopaminergic neuronal survival, and may have important implications for neuroprotection in PD.
Michael K. Kanan, Patrick W. Sheehan, Jessica N. Haines, Pedro G. Gomez, Adya Dhuler, Collin J. Nadarajah, Zachary M. Wargel, Brittany M. Freeberg, Hemanth R. Nelvagal, Mariko Izumo, Joseph S. Takahashi, Jonathan D. Cooper, Albert A. Davis, Erik S. Musiek
Drug-induced liver injury (DILI), especially acetaminophen overdose, is the leading cause of acute liver failure. Pregnane X receptor (PXR) is a nuclear receptor and the master regulator of drug metabolism. Aberrant activation of PXR plays a pathogenic role in the acetaminophen hepatotoxicity. Here, we aimed to examine the PXR S-nitrosylation (SNO) in response to acetaminophen. We found that PXR was S-nitrosylated in hepatocytes and the mouse livers after exposure to acetaminophen or S-nitrosoglutathione (GSNO). Mass-spectrometry and site-directed mutagenesis identified the cysteine 307 as the primary residue for SNO-modification. In hepatocytes, SNO suppressed both agonist (rifampicin and SR12813)-induced and constitutively active PXR (VP-PXR) activations. Furthermore, in acetaminophen overdosed mouse livers, PXR protein was decreased at the centrilobular regions overlapping with increased SNO. In PXR-deficient (PXR-/-) mice, replenishing the livers with the SNO-deficient PXR significantly aggravated hepatic necrosis, increased HMGB1 release, and exacerbated liver injury and inflammation. Particularly, we demonstrated that S-nitrosoglutathione reductase (GSNOR) inhibitor N6022 promoted hepatoprotection by increasing the levels of PXR S-nitrosylation. In conclusion, PXR is post-translationally modified by S-nitrosylation in hepatocytes in response to acetaminophen. This modification mitigated the acetaminophen-induced PXR hyperactivity. It may serve as a target for therapeutical intervention.
Qi Cui, Tingting Jiang, Xinya Xie, Haodong Wang, Lei Qian, Yanyan Cheng, Qiang Li, Tingxu Lu, Qinyu Yao, Jia Liu, Baochang Lai, Chang Chen, Lei Xiao, Nanping Wang
Tuberculosis, a chronic infectious disease caused by a single pathogen, holds the highest mortality rate worldwide. RNA-binding proteins (RBPs) are involved in autophagy — a key defense mechanism against Mycobacterium tuberculosis (Mtb) infection — by modulating RNA stability and forming intricate regulatory networks. However, the functions of host RBPs during Mtb infection remain relatively unexplored. ZNFX1, a conserved RBP critically involved in immune deficiency diseases and mycobacterial infections, is significantly upregulated in Mtb-infected macrophages. Here, we aimed to explore the immune regulatory functions of ZNFX1 during Mtb infection. We observed that Znfx1 knockout markedly compromised the multifaceted immune responses mediated by macrophages. This compromise resulted in reduced phagocytosis, suppressed macrophage activation, increased Mtb burden, progressive lung tissue injury, and chronic inflammation in Mtb-infected mice. Mechanistic investigations revealed that the absence of ZNFX1 inhibited autophagy, consequently mediating immune suppression. ZNFX1 critically maintained AMPK-regulated autophagic flux by stabilizing Prkaa2 mRNA, which encodes a key catalytic α subunit of AMPK, through its zinc finger region. This process contributed to Mtb growth suppression. These findings reveal a function of ZNFX1 in establishing anti-Mtb immune responses, enhancing our understanding of the roles of RBPs in tuberculosis immunity and providing a promising approach to bolster anti-tuberculosis immunotherapy.
Honglin Liu, Zhenyu Han, Liru Chen, Jing Zhang, Zhanqing Zhang, Yaoxin Chen, Feichang Liu, Ke Wang, Jieyu Liu, Na Sai, Xinying Zhou, Chaoying Zhou, Shengfeng Hu, Qian Wen, Li Ma
Pulmonary fibrosis is a chronic and often fatal disease. The pathogenesis is characterized by aberrant repair of lung parenchyma resulting in loss of physiological homeostasis, respiratory failure and death. The immune response in pulmonary fibrosis is dysregulated. The gut microbiome is a key regulator of immunity. The role of the gut microbiome in regulating the pulmonary immunity in lung fibrosis is poorly understood. Here, we determine the impact of gut microbiota on pulmonary fibrosis in C57BL/6 mice derived from different vendors (C57BL/6J and C57BL/6NCrl). We use germ free models, fecal microbiota transplantation and cohousing to transmit gut microbiota. Metagenomic studies of feces establish keystone species between sub-strains. Pulmonary fibrosis is microbiota dependent in C57BL/6 mice. Gut microbiota are distinct by β diversity (PERMANOVA P<0.001) and α diversity (P<0.0001). Mortality and lung fibrosis are attenuated in C57BL/6NCrl mice. Elevated CD4+ IL-10+ T cells and lower IL-6 occur in C57BL/6NCrl mice. Horizontal transmission of microbiota by cohousing attenuates mortality in C57BL/6J mice and promotes a transcriptionally altered pulmonary immunity. Temporal changes in lung and gut microbiota demonstrates that gut microbiota contribute largely to immunological phenotype. Key regulatory gut microbiota contribute to lung fibrosis generating rationale for human studies.
Stephen J. Gurczynski, Jay H. Lipinski, Joshua Y. Strauss, Shafiul Alam, Gary B. Huffnagle, Piyush Ranjan, Lucy H. Kennedy, Bethany B. Moore, David N. O'Dwyer
JCI This Month is a digest of the research, reviews, and other features published each month.