NNI CSF1R Mutation Study: Microglial Dysfunction and Synaptic Impairment in Cerebral Organoids

Singapore's neuroscience community has achieved a significant milestone with a pioneering study from the National Neuroscience Institute (NNI) uncovering the mechanisms behind a rare neurodegenerative condition known as CSF1R-related disorder (CSF1R-RD). Also referred to as adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), this autosomal dominant disease leads to progressive cognitive decline, motor dysfunction, psychiatric symptoms, and white matter abnormalities in the brain. The research, published today in the open-access journal Cell Death Discovery, focuses on a novel mutation in the Colony Stimulating Factor 1 Receptor (CSF1R) gene, T567M, identified in a patient treated at NNI.

Led by Principal Investigator Dr. Li Zeng from NNI's Neural Stem Cell Research Lab, the multidisciplinary team—including collaborators from Duke-NUS Medical School, Nanyang Technological University's Lee Kong Chian School of Medicine, and A*STAR—employed cutting-edge induced pluripotent stem cell (iPSC) technology to model the disease. By generating patient-derived microglia-like cells (iMGL) and cerebral organoids (COs), researchers revealed how the T567M mutation disrupts microglial function and synaptic integrity, offering fresh insights into pathogenesis and potential therapies.

🧠 Understanding CSF1R-Related Disorder and Its Challenges

CSF1R encodes the colony-stimulating factor 1 receptor, a tyrosine kinase receptor essential for the survival, proliferation, and differentiation of microglia—the brain's resident immune cells. These cells maintain neural homeostasis by pruning synapses, clearing debris, and modulating inflammation. Mutations in CSF1R, first identified in 2012, cause CSF1R-RD, affecting approximately 1 in 1,000,000 individuals worldwide, with cases reported globally including Singapore.

Clinically, patients experience insidious onset in adulthood (typically 40-50s), progressing to dementia, pyramidal/extrapyramidal signs, and death within 5-10 years. Brain imaging shows confluent white matter hyperintensities, axonal spheroids, and pigmented microglia. Despite over 100 known mutations—mostly in the kinase domain—the T567M variant, located extracellularly outside this domain, represents a gap in understanding. Prior animal models and postmortem studies implicated microglial loss or dysfunction, but human-specific mechanisms remained elusive due to rarity and ethical constraints on brain tissue.

Singapore's National Neuroscience Institute has diagnosed several cases, highlighting the need for localized research. This study addresses that by using patient peripheral blood mononuclear cells (PBMCs) from an NNI patient, confirming the heterozygous c.1700C>T (p.T567M) mutation via Sanger sequencing.

The Power of iPSC-Derived Human Brain Models

Induced pluripotent stem cells (iPSCs), pioneered by Shinya Yamanaka (Nobel 2012), allow reprogramming of adult cells into embryonic-like states, then differentiation into brain cell types. Here, researchers generated mutant (CSF1R-MT) iPSCs from the patient's PBMCs using Sendai virus, then CRISPR/Cas9-corrected isogenic controls—ensuring genetic identity except the mutation.

From iPSCs, they produced:

• iPSC-derived microglia (iMGL): Via hematopoietic progenitors (HPCs) using STEMdiff kits, maturing over 40 days into ramified cells expressing IBA1, TMEM119, P2RY12.
• Cerebral organoids (COs): Spinner-flask protocol yielding self-organizing mini-brains with cortical layers, matured to day 130.
• Co-cultures: iMGL integrated into COs, mimicking brain-microglia interactions.

This 3D human model bypasses species differences (e.g., rodent microglia diverge from human) and captures patient-specific pathology, validated by confocal imaging, RNA-seq (Illumina), electrophysiology (patch-clamp), and functional assays.

Microglial Dysfunction: Haploinsufficiency and Neuroinflammation

The T567M mutation induced haploinsufficiency: CSF1R protein levels dropped 38-57% in stable cell lines (SH-SY5Y, BV2), with selective loss of autophosphorylation at Tyr546 (56% reduction)—a key signaling site—sparing Tyr708/723. This triggered autophagy (LC3-II/I up 58%) and microglial activation (IBA1 up 179%).

In iMGL:

• Morphology: Reduced area, branches (56% fewer), processes (49% shorter)—less ramified, more amoeboid.
• Function: Impaired migration (88% fewer cells in transwell assay); hyperphagocytosis (61% more beads, 30% more myelin).
• Secretome: LPS challenge upregulated pro-inflammatory cytokines (e.g., CCL2 5x, IL-18 52x via qPCR; proteome array showed broad shifts).
• Transcriptomics: 299 upregulated genes (immune activation: NLRP1, TUBB4A); 1,862 downregulated (synapse/axon pathways: ECM-receptor, PI3K-Akt).

These defects echo ALSP pathology: excessive pruning, failed surveillance, chronic inflammation.

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Synaptic Impairment and Neurodevelopmental Defects

Mutation effects extended to neurons/organoids:

• Neurogenesis: Excess NPC proliferation (Ki67/EdU up 2x); blocked differentiation (TUJ1+ down 84%), maturation (Sholl analysis: 43% fewer dendrites). No added apoptosis.
• Organoids: Fewer MAP2+ neurons (35%); smaller cells (29% less capacitance), hyperpolarized RMP (+24%), higher resistance (+132%). Patch-clamp: Reduced K+ currents, AP firing; sEPSC/IPSC down 75-81%—fewer/ weaker synapses.
• Microglia-neuron interplay: MT iMGL + MT CO co-culture slashed synaptophysin (48%) and PSD95 (75%), confirming non-cell-autonomous synaptic loss.

Findings align with ALSP's synaptic loss, demyelination.

Singapore's Collaborative Neuroscience Excellence

This work exemplifies Singapore's higher education-research synergy. NNI, under SingHealth, partners with Duke-NUS (Neuroscience & Behavioral Disorders Program), NTU (Centre for Molecular Neuropathology), NUS (Physiology), and A*STAR (IMCB). Dr. Li Zeng, holding adjunct roles, bridges clinical care and academia. Similar iPSC efforts at Duke-NUS model Parkinson's, ALS.Explore research positions in Singapore neuroscience.

Singapore invests heavily: RIE2025 allocated S$25B to biomedical sciences, fostering organoid tech at Biopolis. NNI's stem cell lab advances iPSC for ALS, HD.

Broader Implications and Therapeutic Horizons

Beyond mechanisms, the isogenic model enables drug screening: CSF1R agonists (e.g., PLX3397 antagonists reversed rodent defects), microglia transplants, gene editing. Addresses mutation heterogeneity—TKD vs. non-TKD.

Challenges: Rare disease (few patients), organoid variability, scaling. Future: Multi-omics, xenotransplants, AI-phenotyping.

In Singapore, accelerates precision medicine via NSIP, positioning unis as ALSP hubs.Tips for academic CVs in neuroscience.

Stakeholder Perspectives and Real-World Impact

Clinicians like Prof. Eng-King Tan (NNI/Duke-NUS) note earlier diagnosis via genetics. Patients/families gain hope; global registries (e.g., Mayo Clinic) benefit from haplotype data.

Stats: CSF1R-RD penetrance ~100%, but variable onset; Singapore cases underscore diverse mutations. Economic: Neurodegeneratives cost billions; organoids cut animal use 90%.

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Future Outlook: From Organoids to Clinics

Singapore's ecosystem—NNI, Duke-NUS, NTU—pioneers iPSC for rare diseases. Next: Longitudinal studies, combo therapies. Aspiring researchers: Join via higher-ed jobs, university jobs, research roles. Rate professors, career advice.

This NNI-led breakthrough illuminates microglial roles in neurodegeneration, paving personalized treatments.