Nickoloff-Bybel, E. | Search bioRxiv

bioRxiv2025

Linear Z-line-like alignment of capping protein in obliquely striated muscle of the nematode C. elegans suggests that dense bodies are not equivalent to Z-lines

Many invertebrates have obliquely striated muscles, in which neighboring thin and thick filaments are staggered and aligned in an oblique manner. This type of muscle allows force production over a wide range of lengths and is beneficial for soft-bodied animals. Unlike cross-striated muscles of vertebrates, most of obliquely striated muscles lack distinct Z-lines and, instead, have dense bodies. Because the dense bodies are located in the middle of the I-bands and contain -actinin, the dogma is that dense bodies are equivalent to the Z-lines anchoring the actin barbed ends. However, we present evidence that the barbed ends of sarcomeric actin filaments in the nematode Caenorhabditis elegans body wall muscle are aligned in a linear Z-line-like arrangement without converging at the dense bodies. Colocalization of F-actin and ATN-1/-actinin was minimal. Furthermore, CAP-1, an -subunit of capping protein/CapZ, was linearly aligned in the middle of the I-bands without concentration at the dense bodies. This linear CAP-1 alignment was maintained in the absence of ATN-1. These results demonstrate that the actin barbed ends are not directly anchored to the dense bodies. Depletion of the capping protein subunit, CAP-1 or CAP-2, caused embryonic or larval lethality with severe actin disorganization in the body wall muscle, indicating that barbed-end regulation by capping protein is essential for sarcomere assembly. These results contradict the current view of the sarcomere organization in C. elegans muscle and suggest a new model of a linear Z-line-like arrangement of actin barbed ends. Significance StatementO_LIWithout clear evidence, there has been a notion that actin filaments are directly anchored to the dense bodies in C. elegans striated muscle. C_LIO_LICapping protein localizes in a linear Z-line-like alignment in C. elegans muscle without concentrating at the dense bodies, indicating that the actin barbed ends are not directly anchored at the dense bodies. C_LIO_LIDepletion of capping protein causes severe sarcomere defects in embryos and larvae indicating a critical role of capping protein in sarcomere assembly. C_LI

cell biology↗

bioRxiv2024

Dopamine-driven Increase in IL-1β in Myeloid Cells is Mediated by Differential Dopamine Receptor Expression and Exacerbated by HIV

The catecholamine neurotransmitter dopamine is classically known for regulation of central nervous system (CNS) functions such as reward, movement, and cognition. Increasing evidence also indicates that dopamine regulates critical functions in peripheral organs and is an important immunoregulatory factor. We have previously shown that dopamine increases NF-{kappa}B activity, inflammasome activation, and the production of inflammatory cytokines such as IL-1{beta} in human macrophages. As myeloid lineage cells are central to the initiation and resolution of acute inflammatory responses, dopamine-mediated dysregulation of these functions could both impair the innate immune response and exacerbate chronic inflammation. However, the exact pathways by which dopamine drives myeloid inflammation are not well defined, and studies in both rodent and human systems indicate that dopamine can impact the production of inflammatory mediators through both D1-like dopamine receptors (DRD1, DRD5) and D2-like dopamine receptors (DRD2, DRD3, and DRD4). Therefore, we hypothesized that dopamine-mediated production of IL-1{beta} in myeloid cells is regulated by the ratio of different dopamine receptors that are activated. Our data in primary human monocyte-derived macrophages (hMDM) indicate that DRD1 expression is necessary for dopamine-mediated increases in IL-1{beta}, and that changes in the expression of DRD2 and other dopamine receptors can alter the magnitude of the dopamine-mediated increase in IL-1{beta}. Mature hMDM have a high D1-like to D2-like receptor ratio, which is different relative to monocytes and peripheral blood mononuclear cells (PBMCs). We further confirm in human microglia cell lines that a high ratio of D1-like to D2-like receptors promotes dopamine-induced increases in IL-1{beta} gene and protein expression using pharmacological inhibition or overexpression of dopamine receptors. RNA-sequencing of dopamine-treated microglia shows that genes encoding functions in IL-1{beta} signaling pathways, microglia activation, and neurotransmission increased with dopamine treatment. Finally, using HIV as an example of a chronic inflammatory disease that is substantively worsened by comorbid substance use disorders (SUDs) that impact dopaminergic signaling, we show increased effects of dopamine on inflammasome activation and IL-1{beta} in the presence of HIV in both human macrophages and microglia. These data suggest that use of addictive substances and dopamine-modulating therapeutics could dysregulate the innate inflammatory response and exacerbate chronic neuroimmunological conditions like HIV. Thus, a detailed understanding of dopamine-mediated changes in inflammation, in particular pathways regulating IL-1{beta}, will be critical to effectively tailor medication regimens.

neuroscience↗