Biology subjects

Janssen, L.

Publications and source records attributed to Janssen, L..

5 recordsLinked to original sources

bioRxiv2021

Optogenetic manipulation of individual or whole population Caenorhabditis elegans worms with an under hundred-dollar tool: the OptoArm

AbstractOptogenetic tools have revolutionized the study of neuronal circuits in Caenorhabditis elegans. The expression of light-sensitive ion channels or pumps under specific promotors allows researchers to modify the behavior of excitable cells. Several optogenetic systems have been developed to spatially and temporally photoactivate light-sensitive actuators in C. elegans. Nevertheless, their high costs and low flexibility have limited wide access to optogenetics. Here, we developed an inexpensive, easy-to-build, and adjustable optogenetics device for use on different microscopes and worm trackers, called the OptoArm. The OptoArm allows for single- and multiple-worm illumination and is adaptable in terms of light intensity, lighting profiles and light-color. We demonstrate the OptoArms power in a population-based study on contributions of motor circuit cells to age-related motility decline. We find that functional decline of cholinergic neurons mirrors motor decline, while GABAergic neurons and muscle cells are relatively age-resilient, suggesting that rate-limiting cells exist and determine neuronal circuit aging.

genetics↗

bioRxiv2021

Deletion of Serf2 shifts amyloid conformation in an Aβ amyloid mouse model

In age-related neurodegenerative disease, like Alzheimers and Parkinsons disease, disease-specific proteins become aggregation-prone and form amyloid-like deposits. Depletion of SERF proteins ameliorates this toxic process in worm- and human cell models for disease. Whether SERF modifies amyloid pathology in mammalian brain, however, has remained unknown. Here, we generated SERF2 brain-specific knockout mice which, unlike full body knockout mice, were viable, and showed no major behavioral and cognitive abnormalities. We combined these knockout mice with the APPPS1 mouse model for human amyloid beta aggregation. Using structure-specific amyloid dyes, previously used to distinguish amyloid polymorphisms in human brain, we show that knockout of SERF2 alters the structure of amyloid fibrils and deposits. Moreover, scanning transmission electron microscopy revealed thicker, shorter and more densely packed amyloid in absence of SERF2. Altogether, our data reveal pleiotropic functions of SERF in development and aging and support a function as a modifier of amyloid aggregation in mammalian brain. Our results indicate that single cellular factors like SERF can determine the structural outcome of amyloid aggregation, offering possibilities for polymorphism-based disease interventions.

molecular biology↗

bioRxiv2020

The cellular modifier MOAG-4/SERF drives amyloid formation through charge complementation

While aggregation-prone proteins are known to accelerate ageing and cause age-related diseases, the cellular mechanisms that drive their cytotoxicity remain unresolved. The orthologous proteins MOAG-4, SERF1A and SERF2 have recently been identified as cellular modifiers of such cytotoxicity. Using a peptide array screening approach on human amyloidogenic proteins, we found that SERF2 interacted with specific patterns of negatively charged and hydrophobic, aromatic amino acids. The absence of such patterns, or the neutralization of the positive charge in SERF2, prevented these interactions and abolished the amyloid-promoting activity of SERF2. In a protein aggregation model in the nematode C. elegans, protein aggregation was suppressed by mutating the endogenous locus of MOAG-4 to neutralize charge. Our data indicate that charge interactions are required for MOAG-4 and SERF2 to promote aggregation. Such charged interactions might accelerate the primary nucleation of amyloid by initiating structural changes and by decreasing colloidal stability. Our finding that negatively charged segments are overrepresented in amyloid-forming proteins suggests that inhibition of charge interactions deserves exploration as a strategy to target age-related protein toxicity. Significance StatementHow aging causes relatively common diseases such as Alzheimers and Parkinsons is still a mystery. Since toxic structural changes in proteins are likely to be responsible, we investigated biological mechanisms that could drive such changes. We made use of a modifying factor called SERF2, which accelerates structural changes and aggregation of several disease-related proteins. Through a peptide-binding screen, we found that SERF2 acts on negatively charged protein regions. The abundance of such regions in the disease-related proteins explains why SERF has its effect. Removing positive charge in SERF was sufficient to suppress protein aggregation in models for disease. We propose that blocking charge-interactions with SERF or other modifiers could serve as a general approach to treat age-related protein toxicity.

molecular biology↗

bioRxiv2020

The SPPL3-defined glycosphingolipid repertoire regulates immune responses by improving HLA class I access

HLA class I (HLA-I) drives immune responses by presenting antigen-derived peptides to cognate CD8+ T cells. This process is often hijacked by tumors and pathogens for immune evasion. Since therapeutic options for restoring HLA-I antigen presentation are limited, we aimed to identify new HLA-I pathway targets. By iterative genome-wide screens we uncovered that the cell surface glycosphingolipid (GSL) repertoire determines effective HLA-I antigen presentation. We show that absence of the protease SPPL3 augments B3GNT5 enzyme activity, resulting in upregulated levels of surface (neo)lacto-series GSLs. These GSLs sterically impede molecular interactions with HLA-I and diminish CD8+ T cell activation. In accordance, a disturbed SPPL3-B3GNT5 pathway in glioma associates with decreased patient survival. Importantly, we show that this immunomodulatory effect can be reversed through GSL synthesis inhibition using clinically approved drugs. Overall, our study identifies a GSL signature that functionally inhibits antigen presentation and represents a potential therapeutic target in cancer, infection and autoimmunity.

immunology↗

bioRxiv2019

Invariant chain regulates endosomal fusion and maturation through the SNARE Vti1b

Invariant chain (Ii) is an important multifunctional player in the regulation of adaptive immune responses and is responsible for several cellular functions related to MHCI and MHCII antigen loading and antigen presentation. While regulating endosomal trafficking of MHCII and other proteins that bind to Ii, this molecule is able to influence the endosomal pathway delaying the maturation of endosomes to the late endosomal loading compartments. When expressed in cells Ii is found to increase endosomal size, but the mechanisms for this is not known. We used RNAi silencing to identify SNARE proteins controlling Ii induced increase of endosomal size and delay of the endosomal pathway. Ii was found to interact with the SNARE protein Vti1b. Vti1b localized at the contact sites of fusing Ii positive endosomes and a tailless Ii was able to relocate Vti1b to the plasma membrane. Furthermore, silencing Vti1b, abrogated the delay in endosomal maturation induced by Ii expression. In conclusion, Ii interacts with Vti1b and this interaction is fundamental for Ii-mediated alteration of the endosomal pathway. We propose that Ii, by interacting with SNAREs, in particular Vti1B in the biosynthetic pathway of antigen presenting cells, is able to assemble SNARE directed fusion partners in the early part of the endosomal pathway that lead to a slower endosomal maturation for efficient antigen processing and antigen loading.

cell biology↗