Search

Magdalena Gąssowska-Dobrowolska,1 Gabriela Olech-Kochańczyk,1 Carsten Culmsee,2,3 Agata Adamczyk1 1Department of Cellular Signalling, Mossakowski Medical Research Institute, Polish Academy of Sciences, Warsaw, Poland; 2Institute of Pharmacology and Clinical Pharmacy, University of Marburg, Marburg, Germany; 3Center for Mind Brain and Behavior – CMBB, University of Marburg, Marburg, GermanyCorrespondence: Magdalena Gąssowska-Dobrowolska, Email mgassowska@imdik.pan.plAbstract: The prevalence of age-related neurodegenerative diseases, such as Parkinson’s disease (PD) and related disorders continues to grow worldwide. Increasing evidence links intracellular inclusions of misfolded alpha-synuclein (α-syn) aggregates, so-called Lewy bodies (LB) and Lewy neuritis, to the progressive pathology of PD and other synucleinopathies. Our previous findings established that α-syn oligomers induce S-nitrosylation and deregulation of the E3-ubiquitin ligase Parkin, leading to mitochondrial disturbances in neuronal cells. The accumulation of damaged mitochondria as a consequence, together with the release of mitochondrial-derived damage-associated molecular patterns (mtDAMPs) could activate the innate immune response and induce neuroinflammation (“mito-inflammation”), eventually accelerating neurodegeneration. However, the molecular pathways that transmit pro-inflammatory signals from damaged mitochondria are not well understood. One of the proposed pathways could be the cyclic GMP-AMP synthase (cGAS) – stimulator of interferon genes (STING) (cGAS–STING) pathway, which plays a pivotal role in modulating the innate immune response. It has recently been suggested that cGAS–STING deregulation may contribute to the development of various pathological conditions. Especially, its excessive engagement may lead to neuroinflammation and appear to be essential for the development of neurodegenerative brain diseases, including PD. However, the precise molecular mechanisms underlying cGAS–STING pathway activation in PD and other synucleinopathies are not fully understood. This review focuses on linking mitochondrial dysfunction to neuroinflammation in these disorders, particularly emphasizing the role of the cGAS–STING signaling. We propose the cGAS–STING pathway as a critical driver of inflammation in α-syn-dependent neurodegeneration and hypothesize that cGAS–STING–driven “mito-inflammation” may be one of the key mechanisms promoting the neurodegeneration in PD. Understanding the molecular mechanisms of α-syn–induced cGAS–STING–associated “mito-inflammation” in PD and related synucleinopathies may contribute to the identification of new targets for the treatment of these disorders.Keywords: α-synuclein, Parkin, mtDAMPs, mito-inflammation, sterile inflammation, cGAS–STING pathway

Janne Bredehöft,1 Amalia M Dolga,2 Birgit Honrath,2,3 Sybille Wache,1 Sybille Mazurek,1 Carsten Culmsee,3,4 Regien G Schoemaker,5 Rüdiger Gerstberger,1 Joachim Roth,1,4 Christoph Rummel1,4 1Institute of Veterinary Physiology and Biochemistry, Justus Liebig University Giessen, Giessen, Germany; 2Department of Molecular Pharmacology, Groningen Research Institute of Pharmacy, University of Groningen, Groningen, Netherlands; 3Institute of Pharmacology and Clinical Pharmacy, Philipps University of Marburg, Marburg, Germany; 4Center for Mind, Brain and Behavior-CMBB, Giessen and Marburg, Germany; 5Department of Neurobiology, GELIFES, University of Groningen, Groningen, NetherlandsCorrespondence: Christoph RummelInstitute of Veterinary Physiology and Biochemistry, Justus Liebig University Giessen, Frankfurter Strasse 100, Giessen D-35392, GermanyTel +49 641 99 38155Fax +49 641 99 38159Email Christoph.D.Rummel@vetmed.uni-giessen.dePurpose: Previously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.Methods: Mice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.Results: CyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.Conclusion: Overall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.Keywords: neuroinflammation, fever, inflammatory markers, small-conductance calcium-activated potassium channels, locomotor activity, brown adipose tissue