Biology subjects

Ramanujan, A.

Publications and source records attributed to Ramanujan, A..

4 recordsLinked to original sources

bioRxiv2026

Coupling of death receptor p75NTR to the RhoA and NF-kB pathways differentially regulates internalization in hippocampal and cerebellar neurons

Receptor internalization regulates the duration and qualitative output of intracellular signaling. Although generic mechanisms of receptor internalization are well characterized, how these are deployed and regulated in different cell types remains much less understood. Here we show that the p75 neurotrophin receptor (p75NTR), a key regulator of neuron survival and function, internalizes in hippocampal (HCNs)and cerebellar granule (CGNs)neurons with very different kinetics, regulated by distinct mechanisms. Compared to HCNs, p75NTR internalizes at a much slower rate and shows stronger interaction with caveolin in CGNs. In both cell types, p75NTR internalization was enhanced by nerve growth factor (NGF)but reduced by inhibitors of the RhoA and PKC pathways. In line with this, internalization of a p75NTR mutant specifically impaired in RhoA signaling was significantly reduced and insensitive to NGF in both neuron types. Accordingly, this mutant showed a much stronger interaction with caveolin than wild type p75NTR. On the other hand, internalization of a mutant specifically impaired in coupling to the NF-kB signaling pathway was greatly accelerated in CGNs but unaffected in HCNs. These results reveal the crucial role of intracellular signaling in p75NTR internalization and demonstrate that the receptor is differentially wired to the endocytosis machinery in different neuron types, leading to distinct internalization behaviors.

neuroscience↗

bioRxiv2024

Lung CD4+ resident memory T cells use airway secretory cells to stimulate and regulate neutrophilic allergic airways disease.

Neutrophilic asthma is a vexing disease, but mechanistic and therapeutic advancement will require better models of allergy-induced airway neutrophilia. Here, we find that periodic ovalbumin (OVA) inhalation in sensitized mice elicits allergic airway inflammation and pathophysiology mimicking neutrophilic asthma. OVA-experienced murine lungs harbor diverse clusters of CD4+ resident memory TRM cells, including unconventional ROR{gamma}tnegative/low TH17 cells. Acute OVA challenge instigates IL-17A secretion from these TRM cells, driving CXCL5 production from Muc5achigh airway secretory cells, leading to destructive airway neutrophilia. The TRM- and epithelial-cell signals discovered herein are also observed in adult human asthmatic airways. Epithelial antigen presentation regulates this biology by skewing TRM cells towards TH2 and TH1 fates, so that the TH1-related IFN-{gamma} suppresses IL-17A-driven, CXCL5-mediated airway neutrophilia. Concordantly, in vivo IFN-{gamma} supplementation improves disease outcomes. Thus, using our model of neutrophilic asthma we identify lung epithelial-CD4+ TRM cell crosstalk as a key rheostat of allergic airway neutrophilia. HighlightsO_LIRecurrent OVA inhalation experience predisposes mice to allergic airways neutrophilia C_LIO_LINeutrophil-prone lungs harbor CD4+ TRM cells including ROR{gamma}tnegative/low TH17 cells C_LIO_LIMuc5achigh secretory cells instruct CD4+ TRM fates and neutrophilia via MHC-II and CXCL5, respectively C_LIO_LIProphylactic or therapeutic delivery of IFN-{gamma} curbs allergic airway neutrophilia C_LI

immunology↗

bioRxiv2023

RhoGDI phosphorylation by PKC regulates its interaction with death receptor p75NTR to gate axon growth and neuron survival pathways

Although transmembrane receptors engage multiple signaling pathways simultaneously, each pathway is typically investigated individually. How receptors juggle their interactions with different downstream effectors and the conditions under which distinct pathways are prioritized remains poorly understood. Here we show that the outcome of death receptor p75NTR signaling is determined through competition of effectors for interaction with its intracellular domain, in turn dictated by the nature of the incoming ligand. While NGF induces release of RhoGDI through recruitment of RIP2, thus decreasing RhoA activity in favor of NFkB signaling, MAG induces PKC-mediated phosphorylation of the RhoGDI N-terminus, thus promoting its interaction with the juxtamembrane domain of p75NTR, disengaging RIP2, and enhancing RhoA activity in detriment of NF-kB. This results in growth cone collapse, stunted neurite outgrowth and apoptosis in cerebellar granule neurons. If presented simultaneously, MAG prevails over NGF. The NMR solution structure of the complex between the RhoGDI N-terminus and p75NTR juxtamembrane domain reveals previously unknown structures of these proteins and clarifies the mechanism of p75NTR activation. These results show how ligand-directed competition between RIP2 and RhoGDI for p75NTR engagement determine axon growth and neuron survival. Similar principles are likely at work in other receptors engaging multiple effectors and signaling pathways.

neuroscience↗

bioRxiv2021

Structural and functional elucidation of NF-κB signaling by the p75 neurotrophin receptor through recruitment of TRADD

p75 neurotrophin receptor (p75NTR) is a critical mediator of neuronal death and tissue remodeling and has been implicated in various neurodegenerative diseases. The death domain (DD) of p75NTR is an intracellular signaling hub and has been shown to interact with diverse adaptor proteins. However, the structural mechanism and physiological relevance of the adaptor protein TRADD in neuronal p75NTR signaling remain poorly understood. Here we report an NMR structure of the complex between p75NTR-DD and TRADD-DD and elucidate the structural basis of specific DD recognition in the p75NTR/TRADD signaling pathway. Furthermore, we identify spatiotemporal overlap of p75NTR and TRADD expression in developing cerebellar granule neurons (CGNs) at early postnatal stages and reveal the functional role of TRADD recruitment to p75NTR in the regulation of canonical NF-{kappa}B signaling and cell survival in CGNs. Our results provide a new structural framework for understanding how the recruitment of TRADD to p75NTR through DD interactions creates a membrane-proximal platform to propagate downstream signaling in developing neurons.

biophysics↗