Recombinant Human Interferon alpha-inducible protein 27-like protein 2 (IFI27L2)

What is the molecular function of IFI27L2?

IFI27L2 is an interferon-induced protein that plays a significant role in inflammatory processes. The protein is primarily involved in pro-inflammatory cellular mechanisms and has been linked to viral host defense responses. Recent research has demonstrated that IFI27L2 expression is significantly upregulated in response to inflammatory stimuli, particularly in microglia of the aged brain . Mechanistically, IFI27L2 appears to function as a critical neuroinflammatory mediator, with capacity to stimulate mitochondrial ROS production and promote a pro-inflammatory phenotype when induced in microglial cells .

How is IFI27L2 expression regulated at the transcriptional level?

IFI27L2 transcription is primarily regulated through interferon-mediated signaling pathways. Experimental evidence indicates that pro-inflammatory cytokines, particularly TNF-α (20 ng/mL) and IFN-γ (20 ng/mL), significantly upregulate IFI27L2 mRNA expression in human microglial cells (HMC3) . This regulation appears to be time-dependent, with measurable increases in transcript levels within 24 hours of cytokine exposure .

In mouse models, Ifi27l2a (the mouse ortholog) expression follows similar patterns of regulation, showing significant upregulation in response to TNF-α and IFN-γ treatment. Interestingly, the induction of Ifi27l2a appears to follow Il1b expression patterns, suggesting a positive correlation between Ifi27l2a expression and the severity of inflammation (r = 0.848) . This indicates that IFI27L2 expression may be regulated not only by direct interferon signaling but also through secondary inflammatory response pathways.

What cellular compartments contain IFI27L2 protein under normal and stressed conditions?

Immunofluorescence studies of human brain tissue have demonstrated that IFI27L2 expression largely correlates with microglial/macrophage (MG/MΦ) cell types, particularly in inflammatory contexts such as stroke . This suggests that the protein's subcellular localization may be specific to immune-related compartments within these specialized cell types.

What are the established experimental models for studying IFI27L2 function?

Several experimental models have proven valuable for investigating IFI27L2 function:

• Primary Microglial Cultures: Primary mouse microglia collected from mixed glial cell cultures (postnatal day 2 mouse pups) provide an effective system for studying Ifi27l2a expression in response to inflammatory cytokines .

• Human Microglial Cell Line: The HMC3 human microglial cell line serves as an in vitro model for studying IFI27L2 expression in human cells, particularly when challenged with pro-inflammatory cytokines combined with oxygen/glucose deprivation .

• Lentiviral Expression Systems: Microglial cell lines (e.g., Sim-A9 cells) infected with lentiviruses expressing Ifi27l2a under the Cx3cr1 promoter allow for examination of the direct effects of Ifi27l2a overexpression on microglial activation and morphology .

• Hemizygous Deletion Model: Ifi27l2a+/- (Het) mice provide a model for studying the effects of partial reduction in Ifi27l2a expression on inflammatory responses and neurological outcomes following stroke .

• pdMCAO Stroke Model: The permanent distal middle cerebral artery occlusion model in mice enables the investigation of both primary cortical infarct and delayed thalamic inflammation in the context of Ifi27l2a expression and manipulation .

How does IFI27L2 expression change with aging and in pathological conditions?

IFI27L2 expression exhibits significant changes in relation to aging and various pathological conditions:

Age-Related Changes:
Single-cell RNA sequencing (scRNA-seq) of young and aged mouse brains has revealed that Ifi27l2a expression is significantly upregulated in the aged brain, particularly in microglial cells . Quantitative RT-PCR analyses have confirmed elevated Ifi27l2a mRNA levels in both the thalamus and cortex of aged mice compared to young controls .

Ischemic Stroke:
Following ischemic stroke, Ifi27l2a expression is dramatically increased in the brain. In aged mice subjected to permanent distal middle cerebral artery occlusion (pdMCAO), significant upregulation of Ifi27l2a was observed in the ipsilateral cortex at both 3 days and 14 days post-stroke, as well as in the thalamus at 14 days post-stroke . This sustained elevation suggests that Ifi27l2a expression persists into the chronic phase of stroke recovery.

Neurodegenerative Conditions:
Immunofluorescence studies of human brain tissue have shown elevated IFI27L2 expression in the brains of stroke patients with cerebral amyloid angiopathy (CAA) pathology and tauopathy compared to those without these pathological hallmarks . Analysis of open-source single-nucleus RNA-seq data from Alzheimer's disease (AD) postmortem samples demonstrated increased IFI27L2 expression in astrocytes and microglia of the entorhinal cortex compared to age-matched controls .

What techniques are optimal for detecting and quantifying IFI27L2 protein and mRNA?

Researchers have successfully employed multiple techniques for detecting and quantifying IFI27L2:

mRNA Detection and Quantification:

• Quantitative RT-PCR (qRT-PCR): Effectively measures Ifi27l2a/IFI27L2 mRNA levels in tissue samples and cultured cells. RNA isolation from brain regions (thalamus, cortex) followed by qRT-PCR has been used to quantify expression changes in response to aging and stroke .

• Single-Cell RNA Sequencing (scRNA-seq): Provides high-resolution analysis of Ifi27l2a expression at the single-cell level, allowing for identification of cell type-specific expression patterns. This technique has revealed that Ifi27l2a is predominantly expressed in microglial cells and upregulated in aged brains following stroke .

Protein Detection and Quantification:

• ELISA: Successfully used to measure intracellular Ifi27l2a protein levels in mouse primary microglia following treatment with inflammatory cytokines .

• Immunofluorescence: Effective for visualizing IFI27L2 protein expression in human brain tissue samples, particularly in combination with cell type-specific markers such as IBA1 for microglia/macrophages .

• Flow Cytometry: Used in conjunction with cell-specific markers like Tmem119 to isolate and analyze Ifi27l2a-expressing microglial populations from mouse brain tissue .

What is the specific role of IFI27L2 in neuroinflammation following ischemic stroke?

IFI27L2 plays a critical role in promoting and sustaining neuroinflammation following ischemic stroke. Research has identified several key mechanisms:

• Microglial Activation: Elevated Ifi27l2a expression is sufficient to promote microglial activation even in the absence of other inflammatory stimuli. When Ifi27l2a is overexpressed in microglial cells using a lentiviral system, these cells undergo morphological changes characteristic of activation, shifting from a ramified to a more amoeboid morphology . This change in morphology is an early, quantifiable sign of inflammation in microglia and altered microglial functionality.

• Pro-inflammatory Gene Induction: Ifi27l2a overexpression directly induces proinflammatory genes in microglia, including Il1b, Il1a, and Trem2 . This indicates that Ifi27l2a is not merely a marker of inflammation but actively participates in driving the inflammatory response.

• Contribution to Brain Injury: Experimental reduction of Ifi27l2a expression in hemizygous (Ifi27l2a+/-) mice results in significantly reduced cortical infarct volume following permanent distal middle cerebral artery occlusion (pdMCAO) . This protective effect is observed in both male and female mice, suggesting that Ifi27l2a contributes directly to brain injury mechanisms following stroke.

• Mediation of Secondary Injury: In addition to affecting primary infarct, Ifi27l2a also influences secondary injury in remote brain regions. At 14 days post-stroke, reduced Ifi27l2a expression in heterozygous mice is associated with decreased microgliosis in both the primary injury region (somatosensory cortex) and the ipsilateral thalamus, which undergoes delayed secondary injury following cortical stroke .

• Long-term Effects on Brain Atrophy: Reduction of Ifi27l2a expression attenuates long-term brain atrophy, as evidenced by reduced midline shift in heterozygous mice at 4 weeks post-stroke . This demonstrates that Ifi27l2a's effects on neuroinflammation have lasting consequences for brain structure and function.

How does manipulation of IFI27L2 expression affect functional outcomes after neurological injury?

Manipulation of IFI27L2 expression has significant effects on functional outcomes following neurological injury:

Reduction of Ifi27l2a Expression:
Studies using Ifi27l2a+/- (Het) mice have demonstrated that partial reduction of Ifi27l2a expression (approximately 68% reduction) is sufficient to attenuate inflammation and improve outcomes following stroke . Specifically:

• Reduced Inflammatory Response: Primary microglia isolated from Ifi27l2a+/- mice show significantly reduced expression of inflammatory genes (Il1b, Il1a, Tnfa) following LPS challenge compared to wild-type microglia .

• Decreased Primary Injury: At post-stroke day 3, Het mice demonstrate significantly reduced primary cortical infarct volume compared to wild-type mice .

• Attenuated Gliosis: Het mice exhibit reduced microgliosis in the peri-infarct region of the cortex at post-stroke day 14, as well as reduced astrogliosis and microgliosis in the ipsilateral thalamus .

• Improved Long-term Brain Structure: At 4 weeks post-stroke, Het mice show significantly reduced midline shift (measured by iodine contrast-enhanced microCT), indicating less brain atrophy .

• Enhanced Functional Performance: Reduction of Ifi27l2a expression is associated with improved performance in motor-based tests following stroke .

These findings collectively suggest that targeting IFI27L2 could be a viable therapeutic strategy for reducing neuroinflammation and improving functional recovery following stroke or other neurological injuries characterized by inflammation.

What methodological approaches are recommended when investigating IFI27L2 in human disease models?

When investigating IFI27L2 in human disease models, several methodological approaches are recommended:

• Human Microglial Cell Models: The HMC3 human microglial cell line provides a valuable platform for studying IFI27L2 expression and function in response to inflammatory stimuli and oxygen/glucose deprivation . These in vitro models allow for controlled manipulation of IFI27L2 expression and assessment of downstream effects.

• Analysis of Human Postmortem Tissue: Immunofluorescence analysis of brain samples from patients with neurological diseases (e.g., stroke, Alzheimer's disease) can reveal disease-specific patterns of IFI27L2 expression . Co-staining with cell type-specific markers (e.g., IBA1 for microglia/macrophages) helps identify the cellular sources of IFI27L2.

• Single-nucleus RNA Sequencing (snRNA-seq): This technique is particularly valuable for analyzing IFI27L2 expression in human postmortem brain samples, as it provides cell type-specific information while overcoming the challenges associated with isolating intact cells from postmortem tissue .

• Translational Approaches with Partial Expression Reduction: When testing therapeutic strategies, partial reduction of IFI27L2 (rather than complete knockout) may have greater translational potential. Studies with Ifi27l2a+/- mice suggest that even partial reduction can yield significant beneficial effects .

• Multiple Disease Model Comparison: Given that IFI27L2 is elevated in various neuroinflammatory conditions (stroke, Alzheimer's disease, cerebral amyloid angiopathy), comparative studies across different disease models may help identify common and disease-specific mechanisms of IFI27L2 function .

What controls are essential when studying IFI27L2 expression and function?

When designing experiments to study IFI27L2 expression and function, several essential controls should be included:

• Age-Matched Controls: Given the significant influence of aging on IFI27L2 expression, age-matched controls are critical for accurately interpreting expression changes in disease models or aging studies .

• Cell Type-Specific Controls: Since IFI27L2 expression varies considerably across cell types, appropriate cell type-specific markers (e.g., Tmem119 for microglia) should be used to identify and isolate specific cell populations of interest .

• Time-Course Controls: IFI27L2 expression changes dynamically over time following inflammatory stimuli or injury. Multiple time points should be examined to capture both acute and chronic expression patterns .

• Stimulus-Specific Controls: When studying IFI27L2 induction, appropriate stimulus-specific controls are needed. For example, when using viral vectors for gene overexpression, control groups should include vector-only (e.g., eGFP alone) to account for potential effects of viral transduction itself .

• Background Strain Controls: For mouse studies, the genetic background of the animals can influence IFI27L2 expression and responses to stimuli. Wild-type littermates should be used as controls for genetically modified mice .

• Regional Controls: IFI27L2 expression can vary across different brain regions. When studying focal brain injuries like stroke, both ipsilateral and contralateral regions should be examined, along with regions known to undergo secondary damage .

How can researchers effectively model the relationship between IFI27L2 and aging-related inflammation?

Modeling the relationship between IFI27L2 and aging-related inflammation requires a multi-faceted approach:

• Comparative Young vs. Aged Models: Utilizing both young and aged animals allows for direct comparison of baseline IFI27L2 expression and its response to inflammatory stimuli. Single-cell RNA sequencing of young and aged mouse brains has revealed significant age-related differences in Ifi27l2a expression, particularly in microglial cells .

• Region-Specific Analysis: Age-related changes in IFI27L2 expression may vary across brain regions. Quantitative RT-PCR analysis of different brain regions (e.g., cortex, thalamus) can help identify region-specific patterns of expression in relation to aging .

• Cell Type-Specific Isolation: Flow cytometry with cell-specific markers (e.g., Tmem119 for microglia) allows for isolation and analysis of specific cell populations from young and aged brains . This approach can reveal cell type-specific changes in IFI27L2 expression with aging.

• Correlation with Inflammatory Markers: Analysis of the correlation between IFI27L2 expression and established inflammatory markers (e.g., Il1b, Cst7, Tyrobp) in aged brains can provide insights into the relationship between IFI27L2 and aging-related inflammation .

• Challenge Models in Aged Subjects: Comparing the response to inflammatory challenges (e.g., stroke, LPS) between young and aged subjects can reveal age-dependent differences in IFI27L2 induction and function .

• Human Tissue Correlation: Analysis of IFI27L2 expression in human brain tissue across different age groups and in age-related diseases can provide translational insights into the role of IFI27L2 in human aging .

What approaches are recommended for developing therapeutic strategies targeting IFI27L2?

Based on current research, several approaches show promise for developing therapeutic strategies targeting IFI27L2:

• Partial Expression Reduction: Studies with Ifi27l2a+/- mice demonstrate that even partial reduction of Ifi27l2a expression (approximately 68%) can significantly attenuate inflammation and improve outcomes following stroke . This suggests that therapeutic strategies aimed at partially reducing IFI27L2 expression or function may be effective.

• Antisense Oligonucleotide Approaches: Given the success of partial genetic reduction, antisense oligonucleotide-mediated knockdown of IFI27L2 represents a potentially viable therapeutic strategy . This approach would allow for targeted, dose-dependent reduction of IFI27L2 expression.

• Cell Type-Specific Targeting: Since IFI27L2 expression in specific cell types (particularly microglia) appears to drive neuroinflammation, cell type-specific delivery systems could enhance therapeutic efficacy while minimizing off-target effects .

• Temporal Targeting Strategies: The dynamic expression pattern of IFI27L2 following injury suggests that timing is critical for therapeutic intervention. Strategies that target IFI27L2 during specific phases of the inflammatory response may optimize therapeutic outcomes .

• Combination Therapies: Given that IFI27L2 is one of many inflammatory mediators, combination therapies targeting multiple inflammatory pathways may provide synergistic benefits. For example, combining IFI27L2 inhibition with modulation of other interferon-stimulated genes or inflammatory cytokines .

• Translational Validation Across Models: Before advancing to clinical development, therapeutic strategies should be validated across multiple disease models where IFI27L2 is implicated, including stroke, aging, and neurodegenerative diseases such as Alzheimer's disease .

How should contradictory findings regarding IFI27L2 function be reconciled in the literature?

Reconciling contradictory findings regarding IFI27L2 function requires careful consideration of several factors:

What are the most promising future research directions for IFI27L2 in neurological disorders?

Several promising research directions emerge from current knowledge about IFI27L2:

• Mechanistic Studies of IFI27L2 Signaling: Further investigation into the precise molecular mechanisms by which IFI27L2 promotes inflammation, including its role in mitochondrial ROS production and interaction with other inflammatory pathways .

• Development of Specific IFI27L2 Inhibitors: Design and testing of small molecule inhibitors or biologics that specifically target IFI27L2 function for potential therapeutic applications in neuroinflammatory conditions .

• Evaluation in Diverse Neurological Disorders: Extension of IFI27L2 research beyond stroke to other neurological disorders characterized by inflammation, including traumatic brain injury, multiple sclerosis, and neurodegenerative diseases .

• Sex-Specific Effects of IFI27L2: Investigation of potential sex differences in IFI27L2 expression and function, as well as sex-specific responses to IFI27L2-targeted interventions .

• Long-term Consequences of IFI27L2 Manipulation: Evaluation of the long-term effects of IFI27L2 reduction on brain function, cognition, and potential side effects in multiple disease models .

• Biomarker Development: Exploration of IFI27L2 as a potential biomarker for neuroinflammation and disease progression in various neurological disorders .

• Translational Studies in Human Patients: Clinical studies examining IFI27L2 expression in patient samples (e.g., blood, CSF) and correlation with disease progression and outcomes .

How might IFI27L2 function integrate with broader inflammatory networks in disease contexts?

IFI27L2 likely functions as part of a complex inflammatory network in disease contexts:

• Interaction with Interferon Signaling Pathways: As an interferon-stimulated gene, IFI27L2 is part of the broader interferon response network. Recent studies suggest the involvement of type I interferon (IFN-I) signaling in inducing ISGs, including IFI27L2, in the ischemic brain .

• Correlation with Pro-inflammatory Cytokines: IFI27L2 expression shows strong positive correlation with key pro-inflammatory cytokines, particularly Il1b (r = 0.848), suggesting co-regulation or interaction between these inflammatory mediators .

• Role in Microglial Phenotype Regulation: IFI27L2 appears to influence microglial phenotype, promoting a pro-inflammatory state characterized by increased expression of genes such as Il1b, Il1a, and Trem2 . This suggests that IFI27L2 may be a key regulator of microglial activation state.

• Potential Intersection with Age-related Inflammatory Networks: The significant upregulation of IFI27L2 in aged brains suggests it may be part of the age-associated inflammatory network often referred to as "inflammaging" .

• Cross-talk with Neurodegenerative Pathways: The elevated expression of IFI27L2 in human brains with cerebral amyloid angiopathy and tauopathy suggests potential interaction with pathways involved in neurodegenerative processes .

• Contribution to Secondary Injury Mechanisms: IFI27L2's involvement in both primary injury and delayed secondary damage in remote brain regions indicates its integration with broader inflammatory cascades that propagate injury across neural networks .

Understanding these broader network interactions will be crucial for developing effective therapeutic strategies targeting IFI27L2 while accounting for compensatory responses in interconnected inflammatory pathways.