Divergent Ah Receptor Ligand Selectivity during Hominin Evolution

Area of Science:

• Human evolution
• Genetics
• Toxicology

Background:

• The aryl hydrocarbon receptor (AHR) plays a crucial role in mediating responses to environmental toxins.
• Genetic variations in AHR can significantly alter an individual's susceptibility to pollutants.
• Understanding ancient human genetic adaptations is key to comprehending modern human health.

Purpose of the Study:

• To investigate a specific genetic difference in the AHR gene between modern humans and archaic hominins (Neanderthals and Denisovans).
• To functionally characterize the impact of this AHR variant on pollutant binding and transcriptional activity.
• To explore the evolutionary implications of this AHR adaptation in human history.

Main Methods:

• Exome sequence analysis of archaic hominin and modern human DNA.
• Functional assays to assess AHR binding affinity and transcriptional activity.
• Comparative analysis of AHR response to polycyclic aromatic hydrocarbons (PAHs) and endogenous ligands.

Main Results:

• Identified a fixed nonsynonymous single nucleotide polymorphism (SNP) in the AHR ligand-binding domain (Val381 in humans vs. Ala381 in Neanderthals).
• Neanderthal AHR (Ala381) exhibited significantly enhanced binding and transcriptional activity towards PAHs compared to human AHR (Val381).
• Human AHR (Val381) showed retained sensitivity to endogenous ligands while displaying attenuated responses to environmental pollutants like those from fire smoke.

Conclusions:

• A functionally significant AHR variant emerged uniquely in the human lineage, attenuating responses to environmental pollutants.
• This human-specific AHR adaptation may have conferred a survival advantage by reducing toxicity from environmental exposures, such as smoke from cooking fires.
• The findings highlight a critical genetic adaptation in humans related to environmental detoxification and pollutant tolerance.