Spinocerebellar ataxias are genetically heterogeneous inherited neurodegenerative disorders characterized by progressive loss of motor coordination, cerebellar dysfunction and degeneration of Purkinje cells in the cerebellar cortex. Patients commonly show gait instability, speech impairment and poor limb coordination, reflecting disrupted processing of sensory and motor information. SCA14 is caused by mutations in PRKCG, which encodes protein kinase C gamma, or PKCγ. PKCγ is a conventional serine/threonine kinase highly expressed in Purkinje cells and normally maintained in an autoinhibited state in which regulatory domains prevent the kinase domain from phosphorylating substrates. Binding of calcium and diacylglycerol releases this autoinhibition and allows PKCγ to phosphorylate its targets. The kinase regulates dendritic development, cytoskeletal integrity, synaptic plasticity and long-term depression at Purkinje-cell synapses. SCA14-associated mutations can alter kinase activity and disrupt these processes, producing abnormal dendritic architecture, impaired synaptic organization and motor deficits in experimental models.

Investigators tested whether mGluR1 signaling influences Purkinje-cell dysfunction in two mouse models that reproduce aspects of SCA14 but activate PKCγ in different ways. The PKCγ-A24E knockin model carries a point mutation in the kinase’s pseudosubstrate domain, weakening autoinhibition and producing constitutively active PKCγ. The PKCγ-S361G transgenic line expresses a mutant catalytic domain specifically in Purkinje cells and sustains enhanced kinase activity. The researchers used organotypic cerebellar slice cultures and manipulated mGluR1 pharmacologically with 3,5-dihydroxyphenylglycine (DHPG), an mGluR1 agonist, or α-methyl-4-carboxyphenylglycine (MCPG), an mGluR1 antagonist. This design allowed the same receptor-level intervention to be tested against mutations residing in distinct regions of PKCγ and associated with different regulatory behavior. Purkinje cells were identified with calbindin labeling, and dendritic and synaptic measurements were based on microscopy and immunostaining rather than direct recordings of electrical signaling.

In cultures from homozygous PKCγ-A24E animals, MCPG increased Purkinje-cell dendritic area, total branch length and the number of dendritic intersections relative to untreated mutant cultures. The effect was partial rather than a complete return to wild-type structure. Additional experiments in wild-type slices transduced with an adeno-associated virus expressing constitutively active PKCγ in Purkinje cells produced similar, although less pronounced, improvements in dendritic area and branching complexity; branch length did not increase significantly in that setting. The investigators suggested that variability in viral transduction efficiency and expression levels could have influenced cellular responses and limited the degree of morphological rescue. DHPG produced the opposite pattern in wild-type cultures, reducing dendritic area and branch length, consistent with excessive mGluR1 activation exacerbating the phenotype associated with elevated PKCγ activity. These observations were measured in cultured mouse tissue and do not establish that the same intervention would improve structure or motor function in people with SCA14.

Dendritic spines showed parallel changes. PKCγ-A24E Purkinje cells had fewer spines, shorter protrusions and smaller spine heads than wild-type cells. MCPG increased spine density and restored protrusion length and head width. It also increased the proportion of mushroom-shaped spines and reduced immature filopodia, indicating a shift toward a more mature spine architecture. The study did not directly record synaptic transmission, so it cannot establish that the structural rescue produced normal electrical signaling or restored motor coordination. Nevertheless, the findings connect modulation of mGluR1 with both the branching of Purkinje-cell dendrites and the organization of their excitatory postsynaptic compartments. The data also support a mechanistic distinction between the two mutations: in PKCγ-S361G cultures, no significant differences were detected between untreated and MCPG-treated cells in dendritic area, total branch length or intersection number, indicating that mGluR1 inhibition did not influence dendritic morphology in that model.

Postsynaptic scaffolding was similarly disrupted by constitutively active PKCγ and partly restored by mGluR1 inhibition. PKCγ-A24E cultures had fewer Shank2-positive puncta and less Shank2 area than wild-type controls, as well as reduced overlap between Shank2 and mGluR1. MCPG restored Shank2 abundance and area and improved the receptor’s colocalization with the scaffold. Homer3, a direct binding partner of mGluR1, showed a similar pattern: its enrichment, punctum size and colocalization with mGluR1 were reduced in the mutant, but recovered after MCPG treatment. These results indicate that the anatomical rescue involved more than dendritic bulk shape; it also included reorganization of proteins associated with the postsynaptic density. The findings are consistent with a role for the mGluR1-PKCγ pathway in stabilizing postsynaptic components, but the microscopy measurements do not by themselves demonstrate stronger or more effective synaptic transmission.

The investigators further examined GluR2, a subunit of AMPA receptors, and its association with Shank2. GluR2 signal intensity and GluR2-Shank2 colocalization were reduced in PKCγ-A24E Purkinje cells, consistent with diminished enrichment and localization of GluR2-containing AMPA receptors at postsynaptic sites. DHPG also reduced GluR2 enrichment and its association with Shank2 in wild-type cultures, whereas MCPG restored both measures in the mutant. AMPA receptor trafficking participates in synaptic weakening through long-term depression, so the observations suggest a molecular contribution to impaired synaptic efficacy. The study nevertheless measured receptor enrichment and spatial overlap rather than directly measuring receptor currents, long-term depression or other functional synaptic output. The structural and molecular findings therefore support a potential role for mGluR1-dependent regulation of postsynaptic organization, without proving a functional circuit-level benefit.

Biochemical analysis provided a possible link between the receptor intervention and the structural effects. PKC substrate phosphorylation was elevated in homozygous PKCγ-A24E cultures, as expected for the constitutively active mutant, but MCPG reduced this phosphorylation. Total PKCγ protein was also lower in the mutant than in wild-type cultures, so the findings indicate increased kinase activity despite reduced abundance of the protein. MCPG raised PKCγ signal intensity and increased mGluR1-PKCγ colocalization in A24E dendrites, consistent with improved organization of the signaling complex. In PKCγ-S361G cultures, by contrast, MCPG did not change PKC substrate phosphorylation, and the mutant retained elevated PKCγ expression and phosphorylation. The contrast suggests that the A24E kinase remains sensitive to upstream mGluR1-dependent signals even when its catalytic activity is constitutively elevated, whereas the catalytic-domain S361G mutation produces activity that was not reduced by the receptor antagonist under the conditions tested.

The contrast between the two mutations points to an important limitation on any broad description of SCA14 as a single signaling state. A24E weakens the kinase’s regulatory brake and appears to remain responsive to upstream mGluR1-dependent signals. S361G alters the catalytic domain and drives stronger, more sustained activity that was not reduced by mGluR1 inhibition in this system. The investigators proposed that differences in autoinhibition, protein degradation, expression patterns and dependence on calcium and diacylglycerol may explain why the receptor intervention affected A24E but not S361G. The A24E variant is particularly relevant because the study notes that most SCA14-associated mutations are found in the regulatory domain, although it represents only part of the broader mutation landscape. The data therefore support a mutation-specific relationship between mGluR1 and PKCγ rather than a uniform pathway across all SCA14 models. They also extend previous work by linking upstream receptor modulation not only with dendritic morphology but also with spine organization, AMPA-receptor localization and postsynaptic scaffolding.

These results remain preclinical and were obtained in cultured mouse cerebellar tissue, not in people with SCA14. MCPG was used as a laboratory tool rather than tested here as a treatment, and the investigation did not measure motor recovery, long-term behavioral outcomes or clinical safety. Prolonged DHPG exposure may also cause secondary effects, including altered cell viability or receptor trafficking, complicating interpretation of long-term signaling changes; short-term stimulation may be more suitable for separating acute effects from secondary changes associated with chronic exposure. The researchers did not directly trace how calcium and diacylglycerol contribute to continued A24E activity or dissect the downstream events linking mGluR1 activation to mutant PKCγ. Electrophysiological recordings would also be needed to determine whether the observed structural changes translate into improved synaptic output. Nevertheless, the study provides mutation-specific evidence that lowering mGluR1 activity can partially reverse Purkinje-cell dendritic, spine and postsynaptic defects in the PKCγ-A24E model, establishing a signaling relationship that will require functional testing in additional models before it can support therapeutic claims.

Subject of Research: mGluR1 modulation of Purkinje-cell structure and PKCγ signaling in mouse models of SCA14

Article Title: Modulation of mGluR1 signaling improves Purkinje cell dysfunction associated with spinocerebellar ataxia 14

Article References: Sziber, Z., Tang, S., Torrents-Solé, P., Kovacevic, A., & Kapfhammer, J. P. (2026). Modulation of mGluR1 signaling improves Purkinje cell dysfunction associated with spinocerebellar ataxia 14. iScience, 29(11), Article 117976. https://doi.org/10.1016/j.isci.2026.117976

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117976

Keywords: SCA14, spinocerebellar ataxia, mGluR1, PKCγ, Purkinje cells, cerebellum, dendritic morphology, synaptic organization, mouse models, PKCγ-A24E, Modulation, signaling