The technical foundation for this shift in perspective comes from systems biology. By mining curated interaction databases such as STRING and BioGRID and visualizing the results in network analysis platforms like Cytoscape, researchers have assembled maps of the molecular relationships that mutant huntingtin disturbs. Rather than a single linear pathway from misfolded protein to cell death, these maps reveal interconnected modules whose failure propagates through the cell. Crucially, the analysis identifies hub proteins—highly connected nodes such as the molecular chaperone HSP70, the mitochondrial fission regulator DRP1, the inflammatory sensor NLRP3, and the autophagy-controlling transcription factor EB (TFEB)—that act as central control points linking otherwise separate pathways. When a hub fails, the damage radiates outward along many edges at once.

One of the clearest cascades described in the review begins with the ubiquitin-proteasome system, the cell’s primary machinery for shredding damaged or misfolded proteins. Mutant huntingtin impairs this system, so damaged proteins and organelles accumulate. The resulting burden drives mitochondrial oxidative stress: reactive oxygen species rise, ATP production falters, and damaged mitochondria release danger signals. Those signals activate the NLRP3 inflammasome, a multi-protein immune complex best known for igniting inflammation in immune cells. In the Huntington’s brain, chronic NLRP3 activation sustains microglial and astrocyte inflammatory responses, which in turn erode synaptic function. The end point of this cascade is the selective degeneration of medium spiny neurons in the striatum, the cell population whose loss produces the disease’s characteristic uncontrolled movements, psychiatric disturbances, and cognitive decline.

Proteostasis—the cell’s overall management of protein folding, trafficking, and degradation—emerges as a second major battleground. Beyond the ubiquitin-proteasome system, the review details how the autophagy-lysosomal pathway, the cell’s bulk recycling route, is compromised in Huntington’s disease. TFEB, the master transcriptional regulator of lysosomal and autophagy genes, sits at a critical node here; when its activity is suppressed, neurons cannot clear aggregates or damaged mitochondria efficiently. The endoplasmic reticulum adds another layer, with ER stress and ER-mitochondrial crosstalk amplifying the damage. Recent work on polyglutamine-mediated ribotoxicity suggests that the expanded protein tract disrupts proteostasis and stress responses even at the ribosome, meaning the folding crisis begins early in the protein’s life, long before visible aggregates form.

Mitochondrial dysfunction deserves particular attention because it connects nearly every other module in the network. Studies in patient-derived fibroblasts show compromised mitochondrial organization and structure, while DRP1, the dynamin-related protein that governs mitochondrial fission, is dysregulated in the disease. Broken fission-fusion balance means damaged mitochondria cannot be segregated and removed by mitophagy, the specialized autophagy of organelles. Energy metabolism collapses as a result, with the AMP-activated protein kinase and PGC1-alpha regulatory axes—both central to cellular energy sensing—falling out of tune. The review also highlights emerging cell-death mechanisms such as ferroptosis, an iron-dependent form of lipid peroxidation-driven death that links oxidative stress, mitochondria, and the selective vulnerability of striatal neurons.

Perhaps the most consequential claim in the review is temporal: faulty neuroplasticity develops before visible protein aggregates appear. Evidence from the R6/2 and YAC128 transgenic mouse models, from neurons derived from human induced pluripotent stem cells, and from multi-omics studies indicates that synaptic transmission and plasticity are impaired early in the disease course. Brain-derived neurotrophic factor, a growth factor critical for striatal neuron survival whose transport depends on normal huntingtin, is dysregulated long before overt neurodegeneration. RNA granules and RNA-binding proteins such as muscleblind-like protein 1 and ataxin-2 add further early-stage complexity, tying the mutant protein to defects in local translation at synapses. This early dysfunction reframes the therapeutic window: interventions may need to start decades before symptoms, targeting network imbalances rather than waiting to dissolve aggregates.

The network view also explains why genetic modifiers matter so much. Beyond the CAG repeat length, which only partially predicts age of onset, genome-wide studies have identified modifier genes concentrated in DNA repair and interaction-network hubs. Hyperbolic mapping of the protein interaction network and dynamic profiling of huntingtin’s interactions in the striatum have both pointed to candidate modifiers whose normal function buffers the network against the mutant protein’s perturbations. In this framing, disease severity reflects not just the toxic protein but the resilience—or fragility—of the surrounding interaction web, which varies between individuals and shifts with age.

Therapeutically, the review surveys strategies that target the hubs rather than the aggregate itself. Chaperone-based approaches aim to boost HSP70 and the heat shock response governed by HSF1. Selective NLRP3 inflammasome inhibitors have shown neuroprotection in transgenic mouse models, and modulation of the cGAS-STING innate immune pathway represents a newer anti-inflammatory frontier. TFEB activation and small molecules that engage the autophagy-lysosomal pathway, including a p75NTR modulator that reduced huntingtin aggregates in cellular and mouse models, aim to restore cellular clearance. Mitochondria-targeted strategies, from coenzyme Q10 supplementation to compounds that modulate mTORC1 and AMPK/SIRT1/ULK1 signaling, attempt to repair the energy backbone. Epigenetic therapies, notably histone deacetylase inhibitors such as suberoylanilide hydroxamic acid, target the transcriptional dysregulation that silences protective genes.

The most ambitious interventions aim at the source. Antisense oligonucleotides designed to lower mutant huntingtin production have moved from design into clinical testing, while adeno-associated virus-mediated gene therapy approaches are advancing rapidly. The review notes that these nucleic-acid strategies could be combined with network-targeting small molecules, attacking the disease at both its genetic origin and its downstream systems-level consequences. Repurposed drugs, including the tetracycline antibiotic minocycline for its anti-inflammatory effects, and natural compounds such as resveratrol and morin that activate autophagy and antioxidant pathways, illustrate the breadth of the current pipeline.

What makes this review significant is not a single discovery but a change in the map. Huntington’s disease, on this evidence, is a network disorder in which a single expanded protein destabilizes chaperones, proteasomes, mitochondria, inflammasomes, synapses, and chromatin simultaneously—and the hubs that tie these systems together, HSP70, DRP1, NLRP3, and TFEB, are the most promising points of intervention. The authors caution that no datasets were newly generated in their analysis; it is a synthesis, and its power lies in connecting dots across mouse models, human stem-cell systems, and omics data. If the network view holds up in clinical testing, the future of Huntington’s therapy may lie not in one miracle molecule but in combination treatments that hold the entire web together, started early enough to matter.

Subject of Research: Protein-protein interaction networks in Huntington's disease pathogenesis and therapy

Article Title: Uncovering hidden protein networks in Huntington’s disease: implications for pathogenesis and therapy

Article References: Panwar, C., Goel, F., & Garg, V. K. (2026). Uncovering hidden protein networks in Huntington’s disease: implications for pathogenesis and therapy. Molecular Biology Reports, 53(1), Article 1626. https://doi.org/10.1007/s11033-026-12823-6

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12823-6

Keywords: Huntington's disease, mutant huntingtin, protein-protein interaction networks, proteostasis, ubiquitin-proteasome system, autophagy, mitochondrial dysfunction, NLRP3 inflammasome, neuroinflammation, synaptic dysfunction, TFEB, gene therapy

The research team, led by investigators at Barrow Neurological Institute in Phoenix alongside collaborators at the Translational Genomics Research Institute and City of Hope, tackled a persistent blind spot in dementia research. Most studies of diseased brain tissue grind up whole chunks of cortex, producing an average signal in which the synapse’s voice is drowned out by everything else. To overcome this, the researchers isolated synaptosomes, tiny sealed sacs of presynaptic and postsynaptic machinery that pinch off during gentle tissue disruption and can be purified by centrifugation. From frozen frontal cortex samples of ten patients with confirmed C9ORF72-linked FTD and ten neurologically normal donors, obtained through the Queen Square Brain Bank in London, they harvested these synaptic compartments and subjected them to parallel mass spectrometry proteomics and RNA sequencing.

The technical validation was rigorous. Western blots confirmed that the purified fractions were loaded with presynaptic proteins such as synaptophysin and postsynaptic markers like Homer1, while transmission electron microscopy revealed intact membrane-enclosed terminals studded with synaptic vesicles and electron-dense postsynaptic material. Principal component analyses showed that fraction identity, not random variation, was the dominant source of variance in both the protein and RNA datasets, and nuclear markers were largely absent from the synaptic fractions. In other words, the team had genuinely captured the synapse, not a contaminated soup, giving them a trustworthy window onto synaptic biology in the diseased human brain.

What that window revealed was striking. The proteomic analysis identified 1,324 proteins at altered abundance in C9ORF72-FTD synaptosomes, with 555 increased and 769 decreased relative to controls. Pathway analysis using the synapse-specific SynGO database showed that the downregulated proteins clustered heavily around core neurotransmission machinery: the synaptic vesicle cycle, chemical synaptic transmission, and trans-synaptic signaling. Upregulated proteins, by contrast, were modestly enriched for structural remodeling processes such as synapse assembly and postsynaptic actin organization, a pattern the authors interpret as evidence of widespread architectural rebuilding layered on top of failing communication machinery. Many of the altered proteins were unique to the synaptic fraction, and some even shifted in opposite directions between whole tissue and synapses, hinting at localized redistribution of proteins that whole-tissue studies would completely miss.

The RNA side of the story was just as dramatic. Sequencing of synaptosomal RNA uncovered 2,835 differentially expressed protein-coding genes, including 1,763 upregulated and 1,072 downregulated transcripts. When the researchers compared RNA changes with protein changes in the same synaptic compartments, the correlation was only moderate, with a Pearson coefficient of 0.33. Nearly forty percent of the altered genes showed discordant behavior between transcript and protein levels, a signature of broken post-transcriptional regulation inside diseased synapses. In healthy neurons, local RNA and protein abundance are tightly coordinated to keep synaptic transmission running; in C9ORF72-FTD, that coordination visibly frays.

To test whether these brain-tissue signatures could be modeled in the laboratory, the team differentiated induced pluripotent stem cells from C9ORF72-FTD patients and healthy controls into cortical neurons and matured them for one hundred days in culture. The patient-derived neurons showed clear structural deficits: the density of postsynaptic Homer1 puncta at excitatory synapses was reduced, gephyrin puncta at inhibitory synapses were diminished, and the number of fully colocalized inhibitory synapses dropped significantly, even as the corresponding presynaptic markers remained intact. Longitudinal recordings on multielectrode arrays captured a progressive decline in spontaneous network firing between days 65 and 100, indicating worsening hypoexcitability, although the synchrony of network activity was preserved. Notably, this hypoexcitability contrasts with the hyperexcitability often reported in ALS motor neuron models, underscoring that neuronal subtype and disease phenotype shape how the same genetic mutation plays out at the circuit level.

Critically, synaptosomes isolated from these cultured neurons reproduced key molecular pathways seen in the patient brain. The iPSC-derived synaptic proteome contained 962 differentially abundant proteins, and its RNA profile showed 402 differentially expressed protein-coding genes. When the researchers integrated all four datasets, brain protein, brain RNA, iPSC protein, and iPSC RNA, a set of conserved pathways emerged: synapse organization, synapse assembly, regulation of postsynaptic neurotransmitter receptor levels, and trans-synaptic signaling. Among the consistently downregulated genes were members of the neuronal pentraxin family, NPTX1 and NPTXR, which are known to support excitatory synapse formation and have previously been flagged as synaptic biomarkers in the cerebrospinal fluid of genetic FTD patients.

The most surprising discovery, however, came from a targeted search for cryptic exons. When the RNA-binding protein TDP-43 is lost from the nucleus, a hallmark of nearly all FTD and ALS cases, it stops repressing aberrant splice sites, and strange pseudo-exons get stitched into mature transcripts, often destroying the proteins they encode. Cryptic exons in genes like UNC13A and STMN2 are well-documented markers of this process, but they were assumed to be a nuclear phenomenon. The new data show otherwise. In patient synaptosomes, cryptic exon inclusion in STMN2 was significantly increased, detected in eight of ten C9ORF72-FTD cases, and cryptic transcripts of the synaptic scaffolding gene KALRN were also present in a subset of cases. Strikingly, UNC13A cryptic exons were abundant in whole-tissue homogenates but essentially absent from the synaptic fraction, with STMN2 showing the highest synaptic enrichment ratio. This transcript-specific pattern suggests that some aberrantly spliced RNAs are selectively trafficked or retained at synapses rather than randomly redistributed.

The implications ripple outward. STMN2, also known as stathmin-2, is normally transported to distal neuronal compartments where it supports axonal maintenance and repair; KALRN encodes a scaffolding protein central to synaptic signaling and actin remodeling. If cryptic versions of these RNAs accumulate at synapses, they could disrupt local protein synthesis or RNA homeostasis in ways that directly undermine synaptic function, potentially linking TDP-43 loss of function to the synapse loss observed in living patients through neuroimaging and in postmortem tissue. The authors caution that the presence of these transcripts at the synapse does not yet prove they are locally translated or actively toxic, and future work with spatial transcriptomics and high-resolution imaging will be needed to pin down their exact sub-synaptic location and fate.

Limitations remain, as they do in any study of end-stage human disease. The postmortem synaptosomes represent surviving synapses rather than those already eliminated, so some observed changes may reflect compensatory responses rather than primary causes of degeneration. The iPSC cultures, meanwhile, are simplified neuron monocultures lacking the glial cells that shape synapses in the living brain, and they did not show TDP-43 mislocalization or cryptic exons, highlighting gaps in the model. Even so, the convergence of findings across independent systems lends strong support to a reframed view of C9ORF72-FTD: not simply a disease of dying neurons, but a disease in which the synapse, the brain’s most information-dense structure, becomes a site of RNA-level corruption. If synaptic RNA misprocessing proves to be an early event, it could open a new frontier for therapies aimed at preserving synaptic integrity before the damage becomes irreversible.

Subject of Research: Synaptosome multi-omics of C9ORF72-linked frontotemporal dementia reveals synaptic protein and RNA dysregulation and synaptic localization of TDP-43-associated cryptic exon transcripts

Article Title: Integrative synaptosome multi-omics reveals disrupted synapse organization and localized cryptic transcripts in C9ORF72-frontotemporal dementia

Article References: Spillman, A. M., Alsop, E. B., Gittings, L. M., Garcia-Mansfield, K., Piras, I., Bonfitto, A., Martinez, M. N., Sharma, R., Preller, K. R., Huentelman, M., Pirrotte, P., Van Keuren-Jensen, K., & Sattler, R. (2026). Integrative synaptosome multi-omics reveals disrupted synapse organization and localized cryptic transcripts in C9ORF72-frontotemporal dementia. Acta Neuropathologica, 152(1), Article 41. https://doi.org/10.1007/s00401-026-03084-5

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03084-5

Keywords: frontotemporal dementia, C9ORF72, ALS, synaptosome, TDP-43, cryptic exons, proteomics, transcriptomics, iPSC cortical neurons, synaptic dysfunction, STMN2, UNC13A