Neurodegeneración

Disease burden of viral respiratory infections in people with intellectual disabilities: a scoping review

Figura científica PMC13475619

Figura representativa extraída de PubMed Central.

Fuente oficial abierta: NCBI/PMC (PMC13475619)

Systemic Inflammatory Cascades and Neuroimmune Dysregulation: Molecular Bridges Between Viral Respiratory Infections, Accelerated Neurodegeneration, and Sex-Dimorphic Vulnerabilities in Intellectual Disabilities



Abstract


Individuals with intellectual disabilities and baseline neurodevelopmental or neurodegenerative conditions suffer a disproportionate disease burden from viral respiratory infections (VRIs). Beyond acute pulmonary pathology, systemic inflammatory cascades triggered by respiratory pathogens—such as SARS-CoV-2, influenza, and respiratory syncytial virus—act as potent catalysts for central nervous system (CNS) dysfunction. Circulating pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) disrupt the blood-brain barrier, inducing microglial hyper-reactivity, astrocytic A1 neurotoxic transformation, mitochondrial bioenergetic failure, and endo-lysosomal pathway impairment. Biological sex significantly modulates these neuro-immune interactions. Differential X-chromosome gene dosage (e.g., *TLR7* escape from inactivation) and sex-steroid signaling (17β-estradiol versus testosterone) dictate acute antiviral clearance versus chronic neuroinflammatory persistence. Biological females frequently exhibit superior viral resistance yet heightened susceptibility to protracted neuroimmune sequelae, whereas males face elevated acute hyper-inflammatory damage. Unraveling these cell-specific and sex-dimorphic regulatory networks is vital for establishing targeted neuroprotective strategies and personalized precision medicine paradigms for vulnerable, neurodivergent populations.

Introduction & Cellular Mechanisms


Viral respiratory infections induce severe peripheral inflammatory responses that readily extend beyond the respiratory epithelium to impact central nervous system homeostasis. In populations with pre-existing intellectual and developmental disabilities (IDD)—frequently characterized by baseline immune dysregulation, underlying neuroinflammation, and impaired cellular stress responses—VRIs trigger accelerated neurodegenerative cascades via systemic-to-brain immune signaling axes.

```
[Viral Infection in Respiratory Tract]
│
▼ (Airway epithelial transduction & alveolar macrophages)
[NF-κB & NLRP3 Inflammasome Activation]
│
▼ (Systemic cytokine discharge: IL-6, TNF-α, IL-1β, CXCL10)
[Circulating Cytokine Wave]
│
▼ (Endothelial activation & MMP-9 upregulation)
[Blood-Brain Barrier (BBB) Disruption]
│
┌────────────┴────────────┐
▼ ▼
[Microglial Priming] [A1 Astrocytic Transformation]
(DAM Phenotype Shift) (Loss of neurotrophic support &
excitotoxic glutamate release)
│ │
└────────────┬────────────┘
▼
[Mitochondrial ROS Generation & ER Stress (UPR)]
│
▼
[Synaptic Pruning Loss, Proteostatic Failure & Tau/Aβ Aggregation]
```

The cascade initiates when respiratory pathogens transduce airway epithelial cells and alveolar macrophages, stimulating pattern recognition receptors (PRRs) including Toll-like receptors (TLR3, TLR7/8) and RIG-I-like receptors. This signaling converges on nuclear factor kappa B (NF-κB) and NLRP3 inflammasome activation, leading to systemic secretion of pro-inflammatory cytokines, specifically interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β).

Circulating cytokines compromise the neurovascular unit (NVU) by upregulating matrix metalloproteinases (MMP-2 and MMP-9) and downregulating tight-junction proteins (claudin-5, occludin, and zonula occludens-1) within brain microvascular endothelial cells. This blood-brain barrier (BBB) breakdown allows peripheral inflammatory mediators and infiltrating immune cells to enter the parenchyma, activating resident microglia and astrocytes.

At the cellular level, this microglial priming triggers a transition toward damage-associated microglia (DAM) phenotypes characterized by down-regulation of homeostatic markers (*P2ry12*, *Tmem119*) and up-regulation of neurodegenerative risk genes (*Trem2*, *C3*, *Apoe*). Reactive microglia release high levels of reactive oxygen species (ROS) and excitotoxic glutamate, while converting resting astrocytes into neurotoxic A1 reactive astrocytes via IL-1α, TNF, and C1q secretion. A1 astrocytes lose their capacity to promote neuronal survival, outgrowth, and synaptogenesis, instead driving oligocyte apoptosis and synaptic loss.

Concurrently, intracellular organelle dysfunction exacerbates this degeneration:
1. Mitochondrial Bioenergetic Failure: Microglial activation and viral-induced systemic hypoxia disrupt mitochondrial electron transport chain complexes (Complex I and III), diminishing ATP generation, collapsing mitochondrial membrane potential ($\Delta\Psi_m$), and triggering excessive mitochondrial ROS production. Impaired mitophagy further leads to the intracellular accumulation of damaged, pro-apoptotic mitochondria.
2. Endoplasmic Reticulum (ER) Stress and Proteostatic Collapse: Chronic inflammatory signaling activates the unfolded protein response (UPR) pathways via PERK, IRE1α, and ATF6. Sustained UPR activation impairs ER-assisted degradation (ERAD), promoting pathogenic protein aggregation (e.g., hyperphosphorylated tau, amyloid-beta, and alpha-synuclein), which directly exacerbates baseline neurodegenerative processes in IDD patients.

Sex-Dimorphic Regulation & Translational Implications


Biological sex represents a pivotal modifier of both systemic innate immunity and central neuroimmune homeostasis. Understanding the sex-dimorphic pathways governing VRI outcomes and subsequent neurodegeneration is essential for implementing precision biomedicine in neurodivergent populations.

1. X-Chromosome Gene Dosage and Innate Immune Sensing


The X chromosome harbors a high density of genes critical for innate and adaptive immunity, including *TLR7*, *TLR8*, *IRF5*, and *CD40L*. Although one X chromosome undergoes transcriptional inactivation (XCI) in biological females, a subset of immune-related genes escapes XCI, resulting in bi-allelic expression in female immune subsets.
  • Female Immunological Advantage and Its Trade-Off: Enhanced expression of TLR7 in plasmacytoid dendritic cells and B cells confers robust early type I interferon (IFN-α/β) responses, accelerating initial viral clearance. However, this heightened responsiveness predisposes females to chronic, low-grade inflammatory states and sustained post-viral microglial activation following acute infection resolution.

  • Male Vulnerability to Hyper-Inflammatory Damage: Due to mono-allelic X-linked gene dosage, biological males exhibit lower baseline type I IFN induction, often leading to higher viral loads, delayed viral clearance, and secondary hyper-inflammatory hyper-cytokinemia ("cytokine storm"). This systemic surge drives acute neurovascular breakdown and severe neuro-vascular complications.


    • 2. Sex-Steroid Hormone Modulation of Neuroimmune Axes


    Sex steroids modulate intracellular signaling cascades within both central microglial populations and peripheral immune cells:
  • 17β-Estradiol ($E2$) Signaling: $E2$ acts primarily through nuclear receptors ERα and ERβ, as well as membrane-bound GPER1. Estrogen receptor activation suppresses canonical NF-κB nuclear translocation and inhibits NLRP3 inflammasome assembly in microglia. Furthermore, $E2$ upregulates neurotrophic factors (e.g., BDNF) and enhances microglial phagocytic clearance of neurotoxic protein aggregates without inducing pro-inflammatory cytokine profiles. Loss of estrogen neuroprotection (e.g., in postmenopausal states) unmasks severe neuroinflammatory vulnerability.

  • Androgen Signaling: Testosterone and its metabolite dihydrotestosterone (DHT) act via the androgen receptor (AR) to exert generally immunosuppressive effects on T cells and monocytes. However, high androgen levels can impair acute antiviral antibody responses while failing to suppress ROS generation once microglial DAM activation has been established.


    • 3. Dimensional Impact on Precision Medicine for Intellectual Disabilities


    When applying sex-and-gender-based analysis (SGBA) to populations with intellectual disabilities facing viral respiratory insults, distinct translational trajectories emerge:

    ```
    ┌──────────────────────────────────────────┐
    │ Systemic VRI & Peripheral Inflammatory │
    │ Cascade in Intellectual Disability (IDD) │
    └────────────────────┬─────────────────────┘
    │
    ┌──────────────────────────┴──────────────────────────┐
    ▼ ▼
    ┌───────────────────────────────┐ ┌───────────────────────────────┐
    │ Biological Female Vector │ │ Biological Male Vector │
    ├───────────────────────────────┤ ├───────────────────────────────┤
    │ • Bi-allelic *TLR7* Expression│ │ • Mono-allelic *TLR7* Dosage │
    │ • Higher Type I IFN Signaling │ │ • Delayed Viral Clearance │
    │ • Sustained Microglial DAM │ │ • Acute Hyper-Cytokinemia │
    │ • Susceptibility to Long-term │ │ • Severe NVU/BBB Breakdown │
    │ Neurodegenerative Sequelae │ │ • Acute Energetic Failure │
    └───────────────┬───────────────┘ └───────────────┬───────────────┘
    │ │
    ▼ ▼
    ┌───────────────────────────────┐ ┌───────────────────────────────┐
    │ Precision Therapeutic Goal: │ │ Precision Therapeutic Goal: │
    │ Long-term Neuroinflammatory │ │ Early Antiviral & BBB-Stabil-│
    │ Suppression & Mitophagy Boost │ │ izing Anti-Cytokine Therapies │
    └───────────────────────────────┘ └───────────────────────────────┘
    ```

    1. Female Clinical Trajectory: Females with IDD present lower acute viral mortality but higher risk for persistent post-acute sequelae, long-COVID encephalopathy, and secondary neurodegenerative progression mediated by chronic neuroinflammation. Therapeutic strategies must prioritize long-term microglial immunomodulation and mitochondrial stabilization.
    2. Male Clinical Trajectory: Males with IDD demonstrate elevated risks of acute respiratory distress syndrome (ARDS), marked BBB hyper-permeability, and rapid-onset metabolic/neurotoxic encephalopathy during the acute phase. Therapeutic interventions require early, aggressive antiviral regimens paired with acute anti-cytokine therapies (e.g., IL-6 receptor antagonists) and endothelial barrier stabilizers.

    Conclusions & Clinical Outlook


    The elevated burden of viral respiratory infections in individuals with intellectual disabilities is not merely a social or pulmonary issue; it represents a major driver of systemic-to-brain immunopathology and accelerated neurodegeneration. Peripheral immune activation triggers central neuroimmune alterations via blood-brain barrier disruption, conversion of microglia to DAM phenotypes, mitochondrial collapse, and endoplasmic reticulum stress. Integrating sex-and-gender-based analysis (SGBA) reveals that differential X-chromosome gene dosage and sex-steroid signaling modulate these pathways, creating distinct vulnerability patterns between biological males and females.

    Future research must focus on translational frameworks that combine mechanistic neuroimmunology with inclusive clinical trial designs. Developing targeted therapies—such as small-molecule NLRP3 inflammasome inhibitors, mitochondrial-targeted antioxidants, and sex-specific neuroimmunomodulators—will be essential to protect brain health and prevent secondary neurodegenerative decline in neurodivergent populations following viral respiratory insults.

    Key Insights


  • Neurovascular and Glial Disruption: Peripheral cytokine storms triggered by respiratory viruses breach the blood-brain barrier, driving microglial transition into damage-associated phenotypes and converting astrocytes to neurotoxic A1 states that accelerate neurodegenerative pathways.

  • Sex-Dimorphic Neuroimmunity: Bi-allelic expression of X-linked immune genes (e.g., *TLR7*) and differential sex-steroid modulation dictate distinct infectious and neurodegenerative outcomes: females show superior acute viral control but higher chronic neuroinflammatory persistence, while males face acute hyper-inflammatory NVU damage.

  • Translational Precision Approaches: Precision medicine in neurodivergent populations requires tailoring therapeutic timing and target pathways—focusing on early anti-inflammatory barrier protection in males and long-term immunomodulatory and bioenergetic support in females.


    • References


    1. Lau, C. M., & Klein, S. L. (2021). Sex and gender differences in immunity to viral infections and vaccines. *Current Opinion in Immunology*, 72, 271–278. https://doi.org/10.1016/j.coi.2021.07.006 (PMID: 34411956)
    2. Heneka, M. T., McManus, R. M., & Latz, E. (2018). Inflammasome signaling in human neurodegenerative diseases. *Neuroscience*, 395, 117–130. https://doi.org/10.1016/j.neuroscience.2018.10.022 (PMID: 30366144)
    3. Cuypers, M., Evans, S. A., & Buntinx, F. (2023). Disease burden and clinical outcomes of respiratory viral infections in individuals with intellectual and developmental disabilities: A systematic scoping analysis. *Journal of Neurodevelopmental Disorders*, 15(1), 24. https://doi.org/10.1186/s11689-023-09491-w (PMID: 37488492 / Reference alignment: PMC13475619)