Biology subjects

Scheller, J.

Publications and source records attributed to Scheller, J..

6 recordsLinked to original sources

bioRxiv2026

Gp130 Orchestrates a Bidirectional Neuron-Microglia Circuit for neuroprotection

Acquired central nervous system (CNS) injury is one of the most common neurological conditions globally, yet effective treatment options are lacking. As the main tissue-resident macrophages of the CNS, microglia have emerged as key functional regulators of CNS repair. However, means to induce neuroprotective microglia and harness their intrinsic repair capabilities have remained elusive. Here we identify gp130 as a key receptor molecule for facilitating bidirectional microglia-neuron communication that improves outcomes from CNS injury. We show that activation of gp130 in CNS-resident microglia triggers the secretion of leukemia inhibitory factor (LIF), a neurotrophic cytokine. LIF induces neuronal IL-6 secretion that then acts back onto the microglial gp130 receptor, thus creating a neuroprotective loop. We demonstrate the broad therapeutic potential of acute gp130 activation across multiple models, including traumatic brain injury, stroke, and spinal cord injury, and that this pathway can be leveraged therapeutically with designer cytokines.

neuroscience↗

bioRxiv2025

SIRT4 positively regulates autophagy via ULK1, but independently of HDAC6 and OPA1

The sirtuin SIRT4 has been implicated in the control of autophagy and mitochondrial quality control via mitophagy, but the regulatory role of SIRT4 in autophagy/mitophagy induced by different stressors is unclear. Here, we show that cells expressing SIRT4(H161Y), a catalytically inactive, dominant-negative mutant of SIRT4, fail to upregulate LC3B-II and show a reduced autophagic flux upon treatment with different inducers of mitophagy/autophagy, i.e., CoCl2-triggered pseudohypoxia, CCCP/oligomycin-mediated respiratory chain inhibition, or rapamycin treatment. Interestingly, SIRT4(H161Y) expression (i) upregulated protein levels of HDAC6, which is involved in mitochondrial trafficking and autophagosome-lysosome fusion, and (ii) inhibited the conversion of OPA1-L to OPA1-S, which is associated with increased mitochondrial fusion and decreased mitophagy. Both HDAC6 and OPA1 are SIRT4 interactors. However, pharmacological inhibition of neither HDAC6 via Tubacin nor OPA1 via MYLS22 restored the stress-induced upregulation of LC3B-II levels upon autophagy/mitophagy treatment of SIRT4(H161Y)-expressing cells. Remarkably, inhibition of autophagosome-lysosome fusion and thus disruption of late autophagic flux by BafA1 treatment also failed to restore LC3B-II levels upon autophagy/mitophagy treatment, suggesting an inhibitory effect of SIRT4(H161Y) on the initiation/early phase of autophagy. Consistent with this idea, we show that SIRT4(H161Y) promoted the phosphorylation of ULK1 at S638 and S758 (mTORC1 targets), both of which mediate an important inhibitory regulation of autophagy initiation. Thus, our data suggest a positive regulatory function of SIRT4, presumably via modulation of AMPK/mTORC1 signaling, in the ULK1-dependent early regulation/initiation of stress-induced autophagic flux.

biochemistry↗

bioRxiv2023

CoCl2 triggered pseudohypoxic stress induces proteasomal degradation of SIRT4 via polyubiquitination of lysines K78 and K299

SIRT4 comprises together with SIRT3 and SIRT5 the mitochondrially localized subgroup of sirtuins. SIRT4 regulates via its NAD+-dependent enzymatic activities mitochondrial bioenergetics, dynamics (mitochondrial fusion), and quality control (mitophagy). Here, we address the regulation of SIRT4 itself by characterizing its protein stability and degradation upon CoCl2-induced pseudohypoxic stress that typically triggers mitophagy. Interestingly, within the mitochondrial sirtuins, only the protein levels of SIRT4 or ectopically expressed SIRT4-eGFP decrease upon CoCl2 treatment of HEK293 cells. Co-treatment with BafA1, an inhibitor of autophagosome-lysosome fusion required for autophagy/mitophagy, or the use of the proteasome inhibitor MG132 prevented CoCl2-induced SIRT4 downregulation. Consistent with the proteasomal degradation of SIRT4, the lysine mutants SIRT4(K78R) and SIRT4(K299R) showed significantly reduced polyubiquitination upon CoCl2 treatment and were more resistant to pseudohypoxia-induced degradation as compared to SIRT4. Moreover, SIRT4(K78R) and SIRT4(K299R) displayed increased basal protein stability as compared to wild-type SIRT4 when subjected to MG132 treatment or cycloheximide (CHX) chase assays. Thus, our data indicate that stress-induced protein degradation of SIRT4 occurs through two mechanisms, (i) via mitochondrial autophagy/mitophagy, and (ii) as a separate process via proteasomal degradation within the cytoplasm.

biochemistry↗

bioRxiv2022

Alteration of myocardial structure and function in RAF1associated Noonan syndrome: Insights from cardiac disease modeling based on patient-derived iPSCs

Noonan syndrome (NS), the most common among the RASopathies, is caused by germline variants in genes encoding components of the RAS-MAPK pathway. Distinct variants, including the recurrent Ser257Leu substitution in RAF1, are associated with severe hypertrophic cardiomyopathy (HCM). Here, we investigated the elusive mechanistic link between NS-associated RAF1S257L and HCM using three-dimensional cardiac bodies and bioartificial cardiac tissues generated from patient-derived induced pluripotent stem cells (iPSCs) harboring the pathogenic RAF1 c.770C>T missense change. We characterize the molecular, structural and functional consequences of aberrant RAF1 -associated signaling on the cardiac models. Ultrastructural assessment of the sarcomere revealed a shortening of the I-bands along the Z disc area in both iPSC-derived RAF1S257L cardiomyocytes, and myocardial tissue biopsies. The disease phenotype was partly reverted by using both MEK inhibition, and a gene-corrected isogenic RAF1L257S cell line. Collectively, our findings uncovered a direct link between a RASopathy gene variant and the abnormal sarcomere structure resulting in a cardiac dysfunction that remarkably recapitulates the human disease. These insights represent a basis to develop future targeted therapeutic approaches.

cell biology↗

bioRxiv2020

Investigation of fascin1, a marker of mature dendritic cells, reveals a New role for IL-6 signaling in chemotaxis.

Migration of mature dendritic cells (DCs) to lymph nodes is critical for the initiation of adaptive immunity. While CCR7, a a G-protein-coupled receptor for CCL19/21 chemokines, is known to be essential for chemotaxis of mature DCs, the molecular mechanism linking inflammation to chemotaxis remains unclear. We previously demonstrated that fascin1, an actin-bundling protein, increases chemotaxis of mature DCs. In this paper we showed that fascin1 enhanced Interleukin (IL)-6 secretion and signaling. Furthermore, we demonstrated that IL-6 signaling is required for chemotaxis. Blockage of IL-6 signaling in WT DCs with an anti-IL-6 receptor (IL-6R) antibody inhibited chemotaxis toward CCL19. Likewise, knockout (KO) of IL-6R inhibited chemotaxis of BMDCs. The addition of soluble IL-6R and IL-6 rescued chemotaxis of IL-6R KO BMDCs, underscoring the role of IL-6 signaling in chemotaxis. We found that IL-6 signaling is required for internalization of CCR7, the initial step of CCR7 recycling. CCR7 recycling is known to be essential for CCR7-mediated chemotaxis, explaining why IL-6 signaling is needed for chemotaxis of mature DCs. Our results have identified IL-6 signaling as a new regulatory pathway for CCR7/CCL19-mediated chemotaxis, and suggest that rapid migration of mature DCs to lymph nodes depends on inflammation-associated IL-6 signaling.

immunology↗

bioRxiv2020

Subcellular localization and mitotic interactome analyses identify SIRT4 as a centrosomally localized and microtubule associated protein

The stress-inducible and senescence-associated tumor suppressor SIRT4, a member of the family of mitochondrial sirtuins (SIRT3, SIRT4, and SIRT5), regulates bioenergetics and metabolism via NAD+-dependent enzymatic activities. Next to the known mitochondrial location, we found that a fraction of endogenous or ectopically expressed SIRT4, but not SIRT3, is located at the mitotic spindle apparatus in the cytosol. Confocal spinning disk microscopy revealed that SIRT4 localizes during the cell cycle dynamically at centrosomes with an intensity peak in G2 and early mitosis. Moreover, SIRT4 binds to microtubules and interacts with structural (,{beta}-tubulin, {gamma}-tubulin, TUBGCP2, TUBGCP3) and regulatory (HDAC6) microtubule components as detected by co-immunoprecipitation and mass spectrometric analyses of the mitotic SIRT4 interactome. Overexpression of SIRT4 resulted in a pronounced decrease of acetylated -tubulin (K40) associated with altered microtubule dynamics in mitotic cells. SIRT4 or the N-terminally truncated variant SIRT4({Delta}N28), which is unable to translocate into mitochondria, delayed mitotic progression and reduced cell proliferation. This study extends the functional roles of SIRT4 beyond mitochondrial metabolism, and suggests that SIRT4 acts as a novel centrosomal / microtubule-associated protein in the regulation of cell cycle progression. Thus, stress-induced SIRT4 may exert its role as tumor suppressor through mitochondrial as well as extramitochondrial functions, the latter associated with its localization at the mitotic spindle apparatus.

cell biology↗