Biology subjects

Ibanez, C. F.

Publications and source records attributed to Ibanez, C. F..

17 recordsLinked to original sources

bioRxiv2026

p75 neurotrophin receptor signaling through the RhoA/ROCK pathway contributes to Alzheimers Disease tauopathy

Therapeutic development in Alzheimers Disease (AD) has for the most part been focused on reducing {beta}-amyloid load. Nevertheless, neurofibrillary tangles (NFTs), produced by aggregation of hyper-phosphorylated Tau protein, correlate with neurodegeneration and cognitive impairment significantly better than amyloid accumulation in AD patients. Here we report that P301S mice, a model of AD tauopathy, carrying mutant variants of the p75 neurotrophin receptor (p75NTR) deficient in RhoA/ROCK signaling are protected from neurodegeneration and cognitive impairment. Both p75{Delta}DD, lacking the death domain, and triple mutant p75KKEA, unable to interact with RhoGDI, decreased NFT levels, reduced gliosis, neurodegeneration and synapse loss, and improved spatial learning and memory in P301S mice. Intriguingly, p75C259A, a variant unresponsive to neurotrophins but still competent for RhoA signaling induced by myelin-derived ligands, did not afford any neuroprotection. P301S neurons expressing p75{Delta}DD or p75KKEA, but not p75C259A, showed reduced phospho-Tau and ROCK and GSK3{beta} activity, the two main kinases responsible for Tau phosphorylation. In line with this, treatment with myelin-associated glycoprotein (MAG) enhanced Tau phosphorylation and ROCK activity in P301S neurons expressing wild type p75NTR or p75C259A, but not p75{Delta}DD or p75KKEA. Together, these results indicate that p75NTR contributes to AD tauopathy by enhancing the activity of the RhoA-ROCK pathway.

neuroscience↗

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↗

bioRxiv2025

Palmitoylation of death receptor p75NTR contributes to Alzheimer's Disease progression by regulating APP trafficking and degradation

Although protein palmitoylation has been associated with Alzheimers Disease (AD), it remains unclear whether or how palmitoylation of specific proteins contributes to any of the pathological features of AD. The p75 neurotrophin receptor (p75NTR) contributes to AD progression by regulating the intracellular trafficking and amyloidogenic processing of amyloid precursor protein (APP). p75NTR is palmitoylated at a juxtamembrane cysteine but it is currently unknown whether this has any effect on its role in AD. Here, we report that 5xFAD mice, an animal model of AD, expressing a palmitoylation-deficient mutant of p75NTR (p75C281A) display significantly attenuated neuropathology and cognitive deficits. p75C281A showed enhanced internalization, trafficking to Rab5/Rab7 endosomes and lysosomal-mediated degradation. In mutant p75C281A neurons, APP displayed accelerated co-internalization with p75NTR, increased trafficking to late endosomes and lysosome, and enhanced degradation, thereby limiting neuronal A{beta} production. Interestingly, the brain of 5xFAD mice shows increased levels of p75NTR palmitoylation. These results indicate that palmitoylation of p75NTR enhances its stability and, indirectly, that of APP by reducing their trafficking to the lysosome, resulting in increased A{beta} accumulation and neuropathology in the AD brain. Selective inhibitors of p75NTR palmitoylation may find applications in the treatment of AD

neuroscience↗

bioRxiv2025

Effects of different environments and microbial exposures on the adult immune system of the C57BL/6 laboratory mouse strain

The realization that the grossly underdeveloped immune system of laboratory mice may hinder their use as suitable models of human disease has led to the development of different strategies to "normalize" immune responses in these mice so that they more closely resemble those typical of the human population. In this study, we performed a comprehensive comparison of the adult immune systems and microbiomes of C57BL/6 laboratory mice exposed to different housing and microbial conditions. C57/BL6 mice housed in a facility of substandard health levels (herein termed "dirty") and C57BL/6 mice born after embryo transfer from females captured in the field ("wildings") were compared to C57BL/6 mice housed under standard SPF laboratory conditions. Microbiota and parasite burden varied widely between the three conditions, which also showed marked differences among populations of mature, antigen-experienced, memory, plasma, and germinal centre B cells. Interestingly, we observed discrepancies among T cell phenotypes, with antigen-experienced T cells present at higher frequencies in "dirty" mice. On the other hand, "wildlings" displayed significantly elevated frequencies of both naive and antigen-experienced spleen T cells. Interestingly, "dirty" and "wildlings" showed differences in the expansion of distinct myeloid cell types. Lastly, we observed that systemic immune traits reverted to a "cleaner" profile in the progenies (F2) of "wildlings" raised under laboratory conditions, indicating that such mice may not be suitable for human immune system modelling after prolonged housing in laboratory environments. Collectively, our results highlight the profound effects of varied microbial exposures and husbandry conditions on adult immunity of the common C57BL/6 laboratory mouse and suggest that complex microbial exposure in laboratory mice can provide a relevant tool for modelling immunological functions, thus enhancing their translational value.

immunology↗

bioRxiv2025

Neuroprotective function of astrocyte p75NTR in Alzheimer's Disease through regulation of cholesterol metabolism

Reactive astrogliosis in Alzheimers Disease (AD) involves profound changes in the morphology, metabolism and secretion profile of astrocytes, but whether astrogliosis is beneficial or harmful, and under which conditions, remain open questions. Here we report an unexpected neuroprotective function of death receptor p75NTR in astrocytes through its ability to regulate cholesterol metabolism. AD knock-in mice expressing signaling-deficient p75NTR variants in astrocytes showed enhanced A{beta} burden, brain histopathology and cognitive impairment, even when variants were introduced late in the disease process. Astrocytes expressing dysfunctional p75NTR variants showed impaired uptake of A{beta} oligomers, and their conditioned medium enhanced A{beta} production in AD neurons. p75NTR signaling negatively regulated astrocyte cholesterol biosynthesis and secretion, while cholesterol depletion restored A{beta} uptake in mutant astrocytes and reduced A{beta} production in AD neurons. In agreement with the role of astrocyte-derived cholesterol, statin treatment reverted the effects of astrocyte p75NTR mutants on AD neuropathology. Thus, although neuronal p75NTR has been widely recognized to amplify AD, astrocyte p75NTR plays a neuroprotective role.

neuroscience↗

bioRxiv2025

Amelioration of symptomatic Alzheimer's Disease after selective impairment of p75NTR function in adult forebrainexcitatory neurons

The p75 neurotrophin receptor (p75NTR) contributes to the development of Alzheimers Disease (AD) pathology by enhancing amyloid precursor protein (APP) cleavage and amyloid plaque formation. However, the cell type-specific and temporal roles of p75NTR in AD progression remain unclear. Here, we report that conditional knock-in of functionally impaired p75NTR variants lacking the death domain ({Delta}DD) or transmembrane Cys259 (C259A) specifically in forebrain excitatory neurons of 5xFAD mice significantly attenuated multiple AD-associated pathologies, including amyloid plaque accumulation, gliosis, neurite dystrophy, as well as learning and memory deficits. Hippocampal amyloid plaque burden was reduced to levels comparable to those found in whole-body knock-in mice. Strikingly, delaying introduction of p75NTR variants until advanced disease stages produced comparable beneficial effects, and rescued behavior performance in cognitively impaired animals. These findings suggest that blunting p75NTR function can have beneficial effects even during symptomatic stages of AD, offering a potential therapeutic approach complementary to passive vaccination.

neuroscience↗

bioRxiv2023

Impaired migration and metastatic spread of human melanoma by a novel small molecule targeting the transmembrane domain of death receptor p75NTR

Receptor transmembrane domains (TMDs) are crucially involved in relaying ligand information from extracellular to intracellular spaces and represent attractive targets for small molecule manipulation of receptor function. Screening a library of over 8,000 drug-like compounds with an assay based on the TMD of death receptor p75NTR, we identified a novel small molecule capable of inhibiting p75NTR-mediated migration of human melanoma cells. Employing medicinal chemistry, a more potent derivative termed Np75-4A22 was identified that blocks nerve growth factor (NGF)-mediated melanoma invasion at submicromolar concentrations. Mechanistically, Np75-4A22 was found, at least in part, to function by antagonizing NGF-mediated recruitment of the actin-bundling protein fascin to p75NTR and its association with the actin cytoskeleton. Importantly, preclinical assessment of Np75-4A22 showed high oral bioavailability, low toxicity, and significant inhibition of melanoma lung metastases in a highly metastatic mouse model. These results support further development of this approach as an alternative or complementary strategy for patients that do not respond to conventional chemotherapy or immune checkpoint inhibitors.

cancer biology↗

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↗

bioRxiv2023

A distinct subpopulation of adipocytes in adult perirenal adipose tissue arises through brown-to-white conversion but reverts to a thermogenic phenotype upon cold exposure

Perirenal adipose tissue (PRAT) is a unique visceral depot that contains a mixture of brown and white adipocytes. The origin and plasticity of such cellular heterogeneity remains unknown. Here, we combine single-nucleus RNA sequencing with genetic lineage tracing to reveal the existence of a distinct subpopulation of Ucp1-/Cidea+ adipocytes that arises from brown-to-white conversion during postnatal life in the peri-ureter region of mouse PRAT. Cold exposure restores Ucp1 expression and a thermogenic phenotype in this subpopulation. These cells have a transcriptome that is distinct from subcutaneous beige adipocytes and may represent a unique type of cold-recruitable adipocytes. These results pave the way for studies of PRAT physiology and mechanisms controlling the plasticity of brown/white adipocyte phenotypes.

developmental biology↗

bioRxiv2022

Activin receptor ALK4 promotes adipose tissue hyperplasia by suppressing differentiation of adipocyte precursors

Adipocyte hyperplasia and hypertrophy are the two main processes contributing to adipose tissue expansion, yet the mechanisms that regulate and balance their involvement in obesity are incompletely understood. Activin B/GDF-3 receptor ALK7 is expressed in mature adipocytes, and promotes adipocyte hypertrophy upon nutrient overload by suppressing adrenergic signaling and lipolysis. In contrast, the role of ALK4, the canonical pan-activin receptor, in adipose tissue is unknown. Here we report that, unlike ALK7, ALK4 is preferentially expressed in adipocyte precursors, where it suppresses differentiation, allowing proliferation and adipose tissue expansion. ALK4 expression in adipose tissue increases upon nutrient overload and positively correlates with fat depot mass and body weight, suggesting a role in adipose tissue hyperplasia during obesity. Mechanistically, ALK4 signaling suppresses expression of CEBP and PPAR{gamma}, two master regulators of adipocyte differentiation. Conversely, ALK4 deletion enhances CEBP/PPAR{gamma} expression and induces premature adipocyte differentiation, which can be rescued by CEBP knock-down. These results clarify the function of ALK4 in adipose tissue and highlight the contrasting roles of the two activin receptors in the regulation of adipocyte hyperplasia and hypertrophy during obesity.

physiology↗

bioRxiv2022

Dopamine and ALK4 signaling synergize to induce PCBP1-mediated alternative splicing of FosB and sustained behavioral sensitization to cocaine

{Delta}FosB, an alternative spliced product of FosB, is an essential component of dopamine-induced reward pathways and a master switch for addiction. However, the molecular mechanisms of its generation and regulation by dopamine signaling are unknown. Here we report that dopamine D1 receptor signaling synergizes with the activin/ALK4/Smad3 pathway to potentiate the generation of {Delta}FosB mRNA in medium spiny neurons (MSNs) of the nucleus-accumbens (NAc) through activation of the RNA binding protein PCBP1, a regulator of mRNA splicing. Concurrent activation of PCBP1 and Smad3 by D1 and ALK4 signaling induced their interaction, nuclear translocation, and binding to sequences in exon-4 and intron-4 of FosB mRNA. Ablation of either ALK4 or PCBP1 in MSNs impaired {Delta}FosB mRNA induction and nuclear translocation of {Delta}FosB protein in response to repeated co-stimulation of D1 and ALK4 receptors. Importantly, ALK4 was required in NAc MSNs of adult mice for behavioral sensitization to cocaine. These findings uncover an unexpected mechanism for {Delta}FosB generation and drug-induced sensitization through convergent dopamine and ALK4 signaling.

neuroscience↗

bioRxiv2021

Evidence for the equilibrium between monomers and dimers of the death domain of the p75 neurotrophin receptor

The p75 neurotrophin receptor (p75NTR) is an important mediator of synaptic depression and neuronal cell death, and its expression increases upon nerve injury and in neurodegenerative diseases. However, the molecular mechanisms leading to the activation of this receptor are still a matter of debate. The oligomerization properties of the death domain (DD) of p75NTR are critical for our understanding of the activation mechanisms of the receptor. In this paper, we present additional evidence supporting the existence of an equilibrium between monomeric and dimeric forms of the p75NTR DD in solution and in the absence of any other protein. Dynamic light scattering (DLS) measurements of native, untagged human p75NTR DD at room temperature yielded Rh=2.11 for this domain in 20mM phosphate buffer, corresponding to a molecular weight (MW) of approximately 19kDa, much closer to the theoretical MW of the homodimer (i.e. 21kDa) than the monomer. MWs deduced from the Rh of different control proteins used as standards were all congruent with their theoretical MWs. In addition, size-exclusion FPLC profiles of un-tagged human p75NTR DD in both HEPES and phosphate buffers revealed elution volumes corresponding to a MW of about 15kDa, which is intermediate between monomer and dimer, and indicative of dynamic monomer/dimer interconversion during the run. Together with our previous NMR studies, as well as biophysical data for other investigators, these results support the notion that the DD of p75NTR exists in equilibrium between monomers and dimers in solution, a notion that is in agreement with the oligomerization properties of all members of the DD superfamily.

biochemistry↗

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↗

bioRxiv2020

Sustained anti-obesity effects of life-style change and anti-inflammatory interventions after conditional inactivation of the activin receptor ALK7

Life-style change and anti-inflammatory interventions have only transient effects in obesity. It is not clear how benefits obtained by these treatments can be maintained longer term, specially during sustained high caloric intake. Constitutive ablation of the activin receptor ALK7 in adipose tissue enhances catecholamine signaling and lipolysis in adipocytes, and protects mice from diet-induced obesity. Here, we investigated the consequences of conditional ALK7 ablation in adipocytes of adult mice with pre-existing obesity. Although ALK7 deletion had little effect on its own, it synergized strongly with a transient switch to low-fat diet (life-style change) or anti-inflammatory treatment (Na-salicylate), resulting in enhanced lipolysis, increased energy expenditure, and reduced adipose tissue mass and body weight gain, even under sustained high caloric intake. By themselves, diet-switch and salicylate had only a temporary effect on weight gain. Mechanistically, combination of ALK7 ablation with either treatment strongly enhanced the levels of {beta}3-AR, the main adrenergic receptor for catecholamine stimulation of lipolysis, and C/EBP, an upstream regulator of {beta}3-AR expression. These results suggest that inhibition of ALK7 can be combined with simple interventions to produce longer-lasting benefits in obesity.

physiology↗

bioRxiv2020

Inactive variants of death receptor p75NTR reduce Alzheimer's neuropathology by interfering with APP internalization

A prevalent model of Alzheimers disease (AD) pathogenesis postulates the generation of neurotoxic fragments derived from the amyloid precursor protein (APP) after its internalization to endocytic compartments. However, the molecular pathways that regulate APP internalization and intracellular trafficking in neurons are unknown. Here we report that 5xFAD mice, an animal model of AD, expressing signaling-deficient variants of the p75 neurotrophin receptor (p75NTR) show greater neuroprotection from AD neuropathology than animals lacking this receptor. p75NTR knock-in mice lacking the death domain or transmembrane Cys259 showed lower levels of A{beta} species, amyloid plaque burden, gliosis, mitochondrial stress and neurite dystrophy than global knock-outs. Strikingly, long-term synaptic plasticity and memory, which are completely disrupted in 5xFAD mice, were fully recovered in the knock-in mice. Mechanistically, we found that p75NTR interacts with APP and regulates its internalization in hippocampal neurons. Inactive p75NTR variants internalized much slower and to lower levels than wild type p75NTR, favoring non-amyloidogenic APP cleavage by reducing APP internalization and colocalization with BACE1, the critical protease for generation of neurotoxic APP fragments. These results reveal a novel pathway that directly and specifically regulates APP internalization, amyloidogenic processing and disease progression, and suggest that inhibitors targeting the p75NTR transmembrane domain may be an effective therapeutic strategy in AD.

neuroscience↗

bioRxiv2019

Control of brown adipose tissue adaptation to nutrient stress by the activin receptor ALK7

Adaptation to nutrient availability is crucial for survival. Upon nutritional stress, such as during prolonged fasting or cold exposure, organisms need to balance the feeding of tissues and the maintenance of body temperature. The mechanisms that regulate the adaptation of brown adipose tissue (BAT), a key organ for non-shivering thermogenesis, to variations in nutritional state are not known. Here we report that specific deletion of the activin receptor ALK7 in BAT resulted in fasting-induced hypothermia due to exaggerated catabolic activity in brown adipocytes. After overnight fasting, BAT lacking ALK7 showed increased expression of genes responsive to nutrient stress, including the upstream regulator KLF15, aminoacid catabolizing enzymes, notably proline dehydrogenase (POX), and adipose triglyceride lipase (ATGL), as well as markedly reduced lipid droplet size. In agreement with this, ligand stimulation of ALK7 suppressed POX and KLF15 expression in both mouse and human brown adipocytes. Treatment of mutant mice with the glucocorticoid receptor (GR) antagonist RU486 restored KLF15 and POX expression levels in mutant BAT, suggesting that loss of BAT ALK7 results in excessive activation of glucocorticoid signaling upon fasting. These results reveal a novel signaling pathway downstream of ALK7 which regulates the adaptation of BAT to nutrient availability by limiting nutrient stress-induced overactivation of catabolic responses in brown adipocytes.

physiology↗

bioRxiv2019

Activin receptor ALK4 coordinates extracellular signals and intrinsic transcriptional programs to regulate development of cortical somatostatin interneurons

Although the role of transcription factors in fate specification of cortical interneurons is well established, how these interact with extracellular signals to regulate interneuron development is poorly understood. Here we show that the activin receptor ALK4 is a key regulator of the specification of somatostatin interneurons. Mice lacking ALK4 in GABAergic neurons of the medial ganglionic eminence (MGE) showed marked deficits in distinct subpopulations of somatostatin interneurons from early postnatal stages of cortical development. Specific loses were observed among distinct subtypes of somatostatin+/Reelin+ double-positive cells, including Hpse+ layer IV cells targeting parvalbumin+ interneurons, leading to quantitative alterations in the inhibitory circuitry of this layer. Activin-mediated ALK4 signaling in MGE cells induced interaction of Smad2 with SATB1, a transcription factor critical for somatostatin interneuron development, and promoted SATB1 nuclear translocation and repositioning within the somatostatin gene promoter. These results indicate that intrinsic transcriptional programs interact with extracellular signals present in the environment of MGE cells to regulate cortical interneuron specification.

neuroscience↗