Biology subjects

Popper, B.

Publications and source records attributed to Popper, B..

3 recordsLinked to original sources

bioRxiv2020

Extratubular polymerized uromodulin induces leukocyte recruitment and inflammation in vivo

Uromodulin (UMOD) is produced and secreted by tubular epithelial cells. Secreted UMOD polymerizes (pUMOD) within the lumen, where it regulates salt transport and protects the kidney from bacteria and stone formation. Under various pathological conditions, pUMOD accumulates within the tubular lumen and reaches extratubular sites where it may interact with renal interstitial cells. Here, we investigated the potential of extratubular pUMOD to act as a damage associated molecular pattern (DAMP) molecule thereby creating local inflammation. We found that intrascrotal and intraperitoneal injection of pUMOD induced leukocyte recruitment in vivo and led to TNF- secretion by F4/80 positive macrophages. Additionally, pUMOD directly affected vascular permeability and increased neutrophil extravasation independent of macrophage-released TNF-. Interestingly, pUMOD did not directly upregulate adhesion molecules on endothelial cells and did not directly activate {beta}2 integrins on neutrophils. In obstructed neonatal murine kidneys, we observed extratubular UMOD accumulation with tubular atrophy and leukocyte infiltrates. Finally, we found extratubular UMOD deposits associated with peritubular leukocyte infiltration in kidneys from patients with inflammatory kidney diseases. Taken together, we identified extratubular pUMOD as a strong inducer of leukocyte recruitment, underlining its critical role in mounting an inflammatory response in various kidneys pathologies.

immunology↗

bioRxiv2020

Helicobacter hepaticus as disease driver in a novel CD40-mediated model of colitis

Gut microbiota and the immune system are in constant exchange, which shapes both, host immunity and microbial communities. Here, improper immune regulation can cause inflammatory bowel disease (IBD) and colitis. Antibody therapies blocking signaling through the CD40 - CD40L axis showed promising results as these molecules have been described to be deregulated in certain IBD patients. To better understand the mechanism, we used transgenic DC-LMP1/CD40 animals, which lack intestinal CD103+ dendritic cells (DCs) and therefore cannot induce regulatory T (iTreg) cells due to a constitutive CD40-signal in CD11c+ cells. These mice rapidly develop spontaneous fatal colitis with an increase of inflammatory IL-17+IFN-{gamma}+ Th17/Th1 and IFN-{gamma}+ Th1 cells. In the present study we analyzed the impact of the microbiota on disease development and detected elevated IgA- and IgG-levels in sera from DC-LMP1/CD40 animals. Their serum antibodies specifically bound intestinal bacteria and we identified a 60 kDa chaperonin GroEL (Hsp60) from Helicobacter hepaticus (Hh) as the main specific antigen targeted in absence of iTregs. When rederived to a different Hh-free SPF-microbiota, mice showed few signs of disease without fatalities, but upon recolonization of mice with Hh we found rapid disease onset and the generation of inflammatory Th17/Th1 and Th1 cells in the colon. Thus, the present work identifies a major bacterial antigen and highlights the impact of specific microorganisms on modulating the host immune response and its role on disease onset, progression and outcome in this colitis model.

immunology↗

bioRxiv2020

Adaptive mitochondrial regulation of the proteasome

The proteasome is the main proteolytic system for targeted protein degradation in the cell. Its function is fine-tuned according to cellular needs. Regulation of proteasome function by mitochondrial metabolism, however, is unknown. Here, we demonstrate that mitochondrial dysfunction reduces the assembly and activity of the 26S proteasome in the absence of oxidative stress. Impaired respiratory complex I function leads to metabolic reprogramming of the Krebs cycle and deficiency in aspartate. Aspartate supplementation activates assembly and activity of 26S proteasomes via transcriptional activation of the proteasome assembly factors p28 and Rpn6. This metabolic adaptation of 26S proteasome function involves sensing of aspartate via the mTORC1 pathway. Metformin treatment of primary human cells similarly reduced assembly and activity of 26S proteasome complexes, which was fully reversible and rescued by supplementation of aspartate or pyruvate. Of note, respiratory dysfunction conferred resistance towards the proteasome inhibitor Bortezomib. Our study uncovers a fundamental novel mechanism of how mitochondrial metabolism adaptively adjusts protein degradation by the proteasome. It thus unravels unexpected consequences of defective mitochondrial metabolism in disease or drug-targeted mitochondrial reprogramming for proteasomal protein degradation in the cell. As metabolic inhibition of proteasome function can be alleviated by treatment with aspartate or pyruvate, our results also have therapeutic implications.

cell biology↗