Yilmaz, C. | bioRxiv Science

bioRxiv2022

INFLAMMATION INDUCED DOWNREGULATION OF SUCCINATE DEHYDROGENASE REGULATES ADRENOCORTICAL FUNCTION

The hypothalamus-pituitary-adrenal (HPA) axis is activated in response to inflammation leading to increased production of anti-inflammatory glucocorticoids by the adrenal cortex, thereby representing an endogenous feedback loop. However, severe inflammation reduces the responsiveness of the adrenal gland to adrenocorticotropic hormone (ACTH) although the underlying mechanisms are poorly understood. Here, we show by transcriptomic, proteomic and metabolomic analyses that LPS-induced systemic inflammation triggers profound metabolic changes in steroidogenic adrenocortical cells, including downregulation of the TCA cycle and oxidative phosphorylation. Inflammation disrupts the TCA cycle at the level of succinate dehydrogenase (SDH) leading to succinate accumulation and disturbed steroidogenesis. Mechanistically, IL-1{beta} reduces SDHB expression through upregulation of DNA methyltransferase 1 (DNMT1) and methylation of the SDHB promoter. Consequently, increased succinate levels impair oxidative phosphorylation and ATP synthesis, leading to reduced steroidogenesis. Together, we demonstrate that the IL-1{beta}-DNMT1-SDHB-succinate axis disrupts steroidogenesis. Our findings not only provide a mechanistic explanation for the adrenal dysfunction in severe inflammation but also a potential target for therapeutic intervention.

immunology↗

bioRxiv2022

High abundance of transcription regulators compacts the nucleoid in Escherichia coli

In enteric bacteria organization of the circular chromosomal DNA into a highly dynamic and toroidal shaped nucleoid involves various factors such as DNA supercoiling, nucleoid-associated proteins (NAPs), the structural maintenance of chromatin (SMC) complex, and macro-domain organizing proteins. Here we show that ectopic expression of transcription regulators at high levels leads to nucleoid compaction. This serendipitous result was obtained by fluorescence microscopy upon ectopic expression of the transcription regulator and phosphodiesterase PdeL of Escherichia coli of a strain expressing the mCherry-tagged HU- subunit (HupA) for nucleoid staining. Nucleoid compaction by PdeL depends on DNA-binding, but not on its enzymatic phosphodiesterase activity. Nucleoid compaction was also observed upon high-level ectopic expression of the transcription regulators LacI, RutR, RcsB, LeuO and Cra, which range from single target gene regulators to global regulators. In case of LacI its high-level expression in presence of the gratuitous inducer IPTG also led to nucleoid compaction indicating that compaction is caused by unspecific DNA-binding. In all cases nucleoid compaction correlated with misplacement of the FtsZ ring and loss of MukB foci, a subunit of the SMC complex. Thus, high levels of several transcription regulators cause nucleoid compaction with consequences on transcription, replication, and cell division. ImportanceThe bacterial nucleoid is a highly organized and dynamic structure for simultaneous, transcription, replication and segregation of the bacterial genome. Compaction of the nucleoid and disturbance of DNA segregation and cell division by artificially high levels of transcription regulators, as described here, reveals that an excess of DNA-binding protein disturbs nucleoid structuring. The results suggest that ectopic expression levels of DNA-binding proteins for genetic studies of their function but also for their purification should be carefully controlled and adjusted.

microbiology↗