Recently, the Wu Xiaobing team at Genecradle Therapeutics, together with the Zhang Zaiqiang team at Beijing Tiantan Hospital and the Magdalena J. Koziol team at the Chinese Institute for Brain Research, Beijing, published a research paper in the internationally authoritative journal Advanced Science. Zhang Kang of Tiantan Hospital and Ma Wenhao of Genecradle Therapeutics served as co-first authors. The study is the first to demonstrate that a pathological mechanism driven by two NOTCH2NLC-derived pathogenic proteins coexists in Neuronal Intranuclear Inclusion Disease (NIID), providing an entirely new framework for mechanistic research and therapeutic development for NIID.

Paper link: advanced.onlinelibrary.wiley.com/doi/10.1002/advs.76702

I. Background

Neuronal Intranuclear Inclusion Disease (NIID) is a multisystem neurodegenerative disease characterized by widely distributed eosinophilic intranuclear inclusions in the central nervous system and multiple organs. Its clinical presentation is highly heterogeneous, encompassing cognitive impairment, epileptic seizures, leukoencephalopathy, peripheral neuropathy, and autonomic dysfunction, with a progressively worsening disease course.

01 — A Classic Milestone: Establishment of the "Single-Protein" Pathogenic Model

In 2019, the French Boivin team, together with the Wang Zhaoxia team at Peking University First Hospital (Boivin, Wang et al.), published a breakthrough study in Neuron. They were the first to reveal that abnormal GGC repeat expansion in the NOTCH2NLC gene is the principal genetic basis of NIID. The study demonstrated that transcript variant 1 (TV1) can be unconventionally translated through an upstream open reading frame (uORF) into a toxic mini-peptide, uN2CpolyG, which in turn drives inclusion body formation — establishing the "uN2CpolyG single-protein pathogenic model" that the academic community had long accepted.

02 — A Pathological Mystery: The Detection Gap Exposes a "Logical Loophole"

However, the classic model did not fully close the loop. Subsequent pathological studies revealed a key contradiction:

In the brain tissue of NIID patients, the positive labeling rate of pan-generic antibodies for inclusions is as high as 89.5%, whereas the positive detection rate of uN2CpolyG-specific antibodies is only about 56.9%. This mysterious gap of nearly 32.6 percentage points strongly suggests that the uN2CpolyG single-protein model is insufficient to account for the full molecular pathology of NIID, and that other, as-yet-unelucidated pathogenic protein components must be hidden within the inclusions.

03 — Bottleneck and Challenge: A Second Transcript Obscured by High Sequence Homology

In theory, transcript variant 2 (TV2) of NOTCH2NLC, because its GGC repeat sequence lies directly within the coding region (CDS), can be translated into another chimeric polyglycine protein — PolyGN2C-iso2. However, due to the high sequence homology among the NOTCH2NL paralogous gene family, and the long-standing lack of technical tools capable of specifically distinguishing TV2-derived proteins, questions have remained unanswered in the field: Does PolyGN2C-iso2 truly exist in endogenous inclusions? Does it possess autonomous pathogenic capability? It was to crack this bottleneck that the recent study published in Advanced Science broke through years of pathological fog — for the first time confirming both the existence of PolyGN2C-iso2 and its independent pathogenicity, and revolutionizing the understanding of NIID pathology by shifting the disease mechanism from "acting alone" to an entirely new "dual-protein pathology."

II. Key Findings

This study systematically elucidates the key pathological contribution of PolyGN2C-iso2 in NIID across three dimensions: component confirmation, validation of independent pathogenicity, and the core pathogenic mechanism.

01 — Dual Orthogonal Strategy: Confirming PolyGN2C-iso2 as an Inherent Component of NIID Inclusions

To overcome interference from high sequence homology, the research team independently developed specific monoclonal antibodies (M11F6 and M38D5) targeting different epitopes of PolyGN2C-iso2.

Pathological detection: In the skin and skeletal muscle tissues of NIID patients, PolyGN2C-iso2 was confirmed to be widely present in p62-positive intranuclear inclusions. Quantitative analysis showed that 89.0% of p62-positive inclusions were M11F6-positive; among M11F6-positive inclusions, 86.7% were also uN2CpolyG-positive.

Antibody-independent orthogonal validation: The team further used laser capture microdissection (LCM) combined with Skyline targeted proteomics to directly capture the specific distinguishing peptide fragments of PolyGN2C-iso2 in lesion cells from 20 patients. This proteomic evidence provides rigorous orthogonal validation at the molecular level, conclusively confirming PolyGN2C-iso2 as a genuine, inherent component of NIID pathological inclusions.

02 — Breaking the Model Bottleneck: Demonstrating Independent Pathogenicity Through Genecradle's AAV Technology Platform

Previous NIID animal models have often struggled to reproduce the typical cerebral white matter lesions and epileptic phenotypes seen in patients.

Model innovation in this study: Leveraging Genecradle Therapeutics' mature AAV9 intracerebroventricular (ICV) precise central nervous system delivery and transduction technology platform, the team successfully constructed a novel mouse model highly expressing PolyGN2C-iso2.

Phenotype reproduction: In the complete absence of uN2CpolyG, this model faithfully reproduced the core pathological and clinical features of human NIID — inducing widespread intranuclear inclusion formation, cerebral white matter demyelination and ventricular enlargement, spontaneous epileptic-like seizures, spatial memory deficits, and complex psychiatric behavioral abnormalities. This demonstrates that PolyGN2C-iso2 possesses complete pathogenic capability independent of uN2CpolyG.

03 — Mechanistic Depth: Revealing Mitochondrial Dysfunction and a Unique Protein Interaction Network

Combining proteomic analysis of patient lesion tissues with muscle pathology, the study points strongly to mitochondrial dysfunction as the core pathogenic pathway:

Functional impairment: Expression of PolyGN2C-iso2 led to significant reductions in mitochondrial respiratory chain complexes I and IV, severe fragmentation of the mitochondrial network, and abnormal expression of dynamics proteins.

Interaction features: IP-MS interactome comparison showed that although the two toxic proteins exhibit synergy and convergence in the autophagy–proteasome pathway, PolyGN2C-iso2 uniquely enriched mitochondrial outer membrane-associated candidate interaction proteins such as SLC25A3, SLC25A10, and WARS2, suggesting that it has a molecular pathway bias distinct from uN2CpolyG in exerting its pathogenic effects.

III. Research Highlights

A Methodological Benchmark

This study jointly applied two orthogonal strategies — "specific monoclonal antibodies" and "laser capture microdissection–targeted mass spectrometry" — solving the industry-wide challenge of distinguishing human-specific isoforms within highly homologous gene families, and providing a rigorous methodological demonstration for the precise identification of complex homologous proteins and their isoforms.

Model and Technology Platform Empowerment: Genecradle's AAV Delivery Platform Constructs an NIID Disease Model with Clinical Translational Value

The model constructed in this study closely matches the clinical features of human NIID across pathology, imaging, and behavioral dimensions, and in particular overcomes the industry bottleneck of previous models' inability to simulate white matter abnormalities and epileptic-like seizures. The high quality of this model stems both from a deep understanding of the pathological mechanism and from Genecradle Therapeutics' efficient, stable AAV central delivery platform technology. This not only provides a disease model of great clinical translational value for NIID, but also showcases the comprehensive enabling strength of Genecradle's AAV platform in complex neurological disease modeling, target validation, and cutting-edge drug screening.

An Update to the Pathogenic Mechanism: A Cognitive Leap from "Single Protein" to "Dual Protein"

The study breaks with the traditional framework of single-protein-driven pathology, proposing and supporting an expanded model in which uN2CpolyG and PolyGN2C-iso2 jointly participate in NIID pathogenesis, in which PolyGN2C-iso2 is demonstrated to possess independent pathogenic capability. The study further reveals that the two proteins share commonalities in proteostasis regulation and may have different biases in mitochondrial energy metabolism. This provides new clues for resolving the past "historical mystery" in diagnosis and pathological interpretation, and points the way for the future design of precise dual-target/multi-transcript intervention strategies against the NOTCH2NLC gene.

Academic Implications: From Pathogenic Mechanism to Therapeutic Strategy

This study updates the theoretical pathogenic model of NIID and has direct guidance for therapeutic strategy: given that both proteins possess independent pathogenic capability and coexist in patients, future therapeutic interventions may need to target uN2CpolyG and PolyGN2C-iso2 simultaneously to achieve maximal efficacy.

Looking back on the course of this study — launched in 2018 and published in 2026, spanning eight years — from proposing the iso2 toxic macro-protein hypothesis, developing specific tools, accumulating patient tissue evidence, and constructing animal models to completing mechanistic validation, it has been a complete exploration path from fundamental mechanism to precise translation. As one of the corresponding institutions of this study, Genecradle Therapeutics undertook the core technical support of AAV vector process development; its gene therapy drug R&D platform, centered on AAV vector delivery technology, spans the complete chain from target discovery and model validation to potential intervention strategies. It is precisely this platform-based enterprise's technical depth and integration capability that gives a basic study originating from a novel rare disease mechanism a viable foundation for future extension toward gene therapy strategy evaluation and optimization — laying a solid technical base for NIID's progression from pathogenic mechanism to clinical intervention.