iPSC model of CHRFAM7A effect on α7 nicotinic acetylcholine receptor function in the human context

Abstract

The α7 nicotinic acetylcholine receptor (α7nAChR) has been a promising target for diseases affecting cognition and higher cortical functions; however, the effect observed in animal models failed to translate into human clinical trials identifying a translational gap. CHRFAM7A is a human-specific fusion gene with properties that enable incorporation into the α7nAChR and, being human specific, CHRFAM7A effect was not accounted for in preclinical studies. We hypothesized that CHRFAM7A may account for this translational gap and understanding its function may offer novel insights when exploring α7nAChR as a drug target. CHRFAM7A is present in different copy number variations (CNV) in the human genome with high frequency. To study the functional consequences of the presence of the CHRFAM7A, two induced pluripotent stem cell (iPSC) lines (0 copy and 1 copy direct) were developed. The 0 copy line was rescued with CHRFAM7A transfection to control for genetic heterogeneity. As readouts for genotype–phenotype correlation, α7nAChR synaptic transmission and amyloid beta 1–42 (Aβ1–42) uptake were tested. Synaptic transmission in the presence of CHRFAM7A demonstrated that PNU-modulated desensitization of α7nAChR currents increased as a function of CHRFAM7A dosage. CHRFAM7A mitigated the dose response of Aβ1–42 uptake suggesting a protective effect beyond physiological concentrations. Furthermore, in the presence of CHRFAM7A Aβ1–42 uptake activated neuronal interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) without activating the canonical inflammasome pathway. Lead optimization may identify more potent molecules when the screen has a model harboring CHRFAM7A. Incorporating pharmacogenetics into clinical trials may enhance signals in efficacy measures.

CHRFAM7A: A human specific fusion gene, accounts for the translational gap for cholinergic strategies in Alzheimer's disease

“…1 a, c, d). In contrast, CHRFAM7A transfected cells (direct model) had a decreased channel open probability, similar to the previously reported UB052 iPSC line, carrier of CHRFAM7A [11] . To aid surface expression of α7, co-transfection with intracellular chaperones Ric-3 [18] and NACHO [19] in 1:1:1 ratio was applied in all experiments.…”

“…CHRFAM7AΔ 2 bp allele behaved as a functional null for channel function, while CHRFAM7A decreased channel open time indicating dominant negative effect. In the presence of CHRFAM7A allele, Aβ 1–42 uptake was mitigated at post-physiological levels [11] while CHRFAM7AΔ 2 bp showed similar dose response as the null line. Both neuronal toxicity and Aβ 1–42 uptake were dose-dependent and were mitigated by CHRFAM7A , but not by CHRFAM7AΔ 2 bp.…”

“…Previously, we showed that CHRFAM7A mitigates Aβ 1–42 uptake, but the functional role of the CHRFAM7AΔ 2 bp allele remained unknown. To address this question, UB068 iPSCs [11] harbouring two ancestral alleles (0 copy) were differentiated into MGE progenitors[ 26 , 14 ] and transfected with an empty vector, EV (pcDNA3.3-mCherry ), CHRFAM7A (pcDNA3.1-CHRFAM7A-mCherry) and CHRFAM7AΔ 2 bp (CHRFAM7ADelta2bp-mCherry)[ 17 , 11 ]. Expression of CHRFAM7A and CHRFAM7AΔ 2 bp was confirmed by breakpoint specific RT-qPCR ( Supplementary Fig.…”

“…3 a, b). As a nascent CHRFAM7A carrier, UB052 was incorporated into the panel [11] . In all three lines, fluorescent Aβ 1–42 uptake assessed by cell counts showed genotype specific dose response curves ( Fig.…”

“…As a result, in the absence of stimulation by Pathogen-associated molecular pattern molecules (PAMPs) and perhaps Damage-associated molecular patterns (DAMPs) an anti-inflammatory milieu is set by donepezil [12] . Once an immune trigger in present, such as LPS or Aβ, CHRFAM7A refines the inflammatory tone to activate the innate immune response [ 11 , 36 ]. These immune regulatory differences between rat (non-carriers of CHRFAM7A) and humans (studied lines are CHRFAM7A carriers) could account for the DMT effect in non-carriers by controlling Aβ (DAMP) triggered neuroinflammation.…”