IPSC-Derived Microglia for Modeling Human-Specific DAMP and PAMP Responses in the Context of Alzheimer's Disease.

Ivanna Ihnatovych,Kinga Szigeti,Emily Notari,Barbara Birkaya

doi:10.3390/ijms21249668

Abstract

Neuroinflammation in Alzheimer’s disease (AD) has been the focus for identifying targetable pathways for drug development. The role of amyloid beta (Aβ), a prototype of damage-associated molecular patterns (DAMPs), has been implicated in triggering an inflammatory response. As alpha7 nicotinic acetylcholine receptor (α7 nAChR) binds Aβ with high affinity, α7 nAChR may play a role in Aβ-induced neuroinflammation. The conundrum of how α7 nAChR as the mediator of the cholinergic anti-inflammatory response may trigger an inflammatory response has not been resolved. CHRFAM7A, the uniquely human fusion gene between ULK4 and CHRNA7, is a negative regulator of α7 nAChR ionotropic function. To provide the human context, isogenic induced pluripotent stem cell (iPSC) lines were developed from CHRFAM7A null and carrier individuals by genome-editing the null line using TALENs to knock-in CHRFAM7A. In iPSC-derived microglia-like cells, CHRFAM7A mitigated Aβ uptake through the α7 nAChR. Despite the lower Aβ uptake, the presence of CHRFAM7A was associated with an innate immune response that was characterized by NF-κB activation and NF-κB target transcription (TNFA, IL6, and IL1B). LPS, a prototype PAMP, induced a heightened immune response in CHRFAM7A carriers. CHRFAM7A modified the dynamics of NF-κB translocation by prolonging its nuclear presence. CHRFAM7A modified the α7 nAChR metabotropic function, resulting in a human-specific innate immune response. This iPSC model provided an opportunity to elucidate the mechanism and establish high throughput screens.

Highlights

Neuroinflammation has emerged as a targetable mechanism in Alzheimer’s disease (AD) over the last ten years, which has been driven by GWAS (Genome Wide Association Studies) signals in several genes (CR1, CLU, triggering receptor expressed on myeloid cells 2 (TREM2), HLA-DRB5/DRB1, INPP5D, and MEF2C) that are implicated in inflammation [1]
The MGLp1bco,esilltoliswvederfioffrroewsrue)r.nfTatchiaeetmMedaGrkfLreocresmllCsDtdh1ief1fbetr,heCrnDetie6a8tie,PdaSnfCrdomilninttrheaescetelhlxureplaerreiPcsaSslCecidulimnme-sbicienrxdopigrnelgsisape-drsopmteeiicncrifioIbgcali-ma1-s(aFpriekgcueifrriecs (Figure 1c) and demmonarskterrast(eFdiguarech1ca)raancdtedreimstoincstmraoterdpahochlaorgacyte(rFisitgicumreorp1hdo,lougpy p(Feirgurroew1d), aunppderaropwo)saitnidvea stain with microgliap-sopsieticviefisctatirnawnisthmmemicrbogralina-espperciofitcetirnanTsMmeEmMbr1a1n9e p(FroitgeuinreTM1dEM, l1o1w9.d,Tlohweefrurnowct)i.oTnhael activity of the MGLfcuenlcltsiownaal sacdtievimtyoonf sthteraMteGdL vceilalspwhaas gdoemcyotnisctraatcetdivviitaypuhasginocgytflicuaoctrievistcyeunstinlgaftleuxorbesecaedntsla(Fteixgure 1e)
Similar to our previous finding in neural progenitor cells (NPCs) [20,21], we found a hypomorphic effect of CHRFAM7A on the Aβ uptake phenotype in MGL cells

Summary

Introduction

Neuroinflammation has emerged as a targetable mechanism in Alzheimer’s disease (AD) over the last ten years, which has been driven by GWAS (Genome Wide Association Studies) signals in several genes (CR1, CLU, TREM2, HLA-DRB5/DRB1, INPP5D, and MEF2C) that are implicated in inflammation [1]. While the role of Aβ in neuroinflammation is complex, the interaction between Aβ and α7 nAChR has produced a conundrum [2,3,4,5]. The α7 nAChR localization pattern correlates with areas in the human brain that are affected in early AD pathology [7]. The complex interaction between the nervous and immune systems is required in in vivo physiological experimentation using animal models; the cholinergic anti-inflammatory system emerged from animal observations. While α7 nAChR has been an active drug target in AD for over a decade, the vast cumulative preclinical and clinical data revealed one of the most consistent translational gaps between animal models and human trials [9]

Methods

Results

Discussion

Conclusion