Human-specific SNP in obesity genes, adrenergic receptor beta2 (ADRB2), Beta3 (ADRB3), and PPAR γ2 (PPARG), during primate evolution

Abstract

Adrenergic-receptor beta2 (ADRB2) and beta3 (ADRB3) are obesity genes that play a key role in the regulation of energy balance by increasing lipolysis and thermogenesis. The Glu27 allele in ADRB2 and the Arg64 allele in ADRB3 are associated with abdominal obesity and early onset of non-insulin-dependent diabetes mellitus (NIDDM) in many ethnic groups. Peroxisome proliferator-activated receptor γ (PPARG) is required for adipocyte differentiation. Pro12Ala mutation decreases PPARG activity and resistance to NIDDM. In humans, energy-expense alleles, Gln27 in ADRB2 and Trp64 in ADRB3, are at higher frequencies than Glu27 and Arg64, respectively, but Ala12 in PPARG is at lower frequency than Pro12. Adaptation of humans for lipolysis, thermogenesis, and reduction of fat accumulation could be considered by examining which alleles in these genes are dominant in non-human primates (NHP). All NHP (P. troglodytes, G. gorilla, P. pygmaeus, H. agilis and macaques) had energy-thrifty alleles, Gly16 and Glu27 in ADRB2, and Arg64 in ADRB3, but did not have energy-expense alleles, Arg16, Gln27 and Trp64 alleles. In PPARG gene, all NHP had large adipocyte accumulating type, the Pro12 allele.

Conclusions: These results indicate that a tendency to produce much more heat through the energy-expense alleles developed only in humans, who left tropical rainforests for savanna and developed new features in their heat-regulation systems, such as reduction of body hair and increased evaporation of water, and might have helped the protection of entrails from cold at night, especially in glacial periods.

Figure 1. Nucleotide sequences in ADRB2 of humans and NHPs.

Primers 16HF and 16HRc (Rc means the complementary sequence of reverse primer) indicate a primer set used for the PCR to amplify the region for the 16^th amino acid in hominoids. One nucleotide of primer 16HF was changed to create the restriction site of BsrDI. Primers 27MF and 27MRc indicate a primer set used for the PCR to amplify the region for the 27^th amino acid in macaques. The underlines show the restriction site (GCAATGNN) with BsrDI for the 16^th amino acid and the restriction site (GCNGC) with ItaI for the 27^th amino acid. The nucleotide sequences for hominoids were determined from G. gorilla (DDBJ Accession No. AB669098), P. pygmaeus (AB669099) and H. agilis (AB669100), and obtained from the Ensembl database for ADRB2 of H. sapiens (ENSG00000169252) and P. troglodytes (ENSPTRG00000017391). All macaques, M. fascicularis, M. fuscata, M. nemestrina, M. radiata (AB669101∼AB669104, respectively) and M. mulatta (ENSMMUG 00000002214), show the same sequence.

Figure 2. All hominoids had Gly16 allele in ADRB2.

A) Restriction map of ADRB2 for the 16^th amino acid digested with BsrDI (GCAATGNN). This restriction map was predicted from the nucleotide sequences of hominoids (Fig. 1). B) RFLP patterns of PCR products of ADRB2 for the 16^th amino acid digested with BsrDI in hominoids. Lane 1: PCR product of a human; not digested (200 bp). Lane 2: Fragments of human Arg16/Gly16 (130,108 and 56 bp (22 and 14 bp fragments were undetectable)). Lane 3 to lane 6: Fragments from P. troglodytes, G. gorilla, P. pygmaeus, and H. agilis, respectively (108 and 22 bp instead of 130 bp).

Figure 3. All NHP had Glu27 allele in ADRB2.

A) Restriction map of ADRB2 for the 27^th amino acid digested with ItaI. This restriction map was predicted from the nucleotide sequences of humans (Ensembl database ENSG00000169252) and P. troglodytes (Ensembl database ENSPTRG00000017391) and from obtained macaque nucleotide sequences (Fig. 1). B) RFLP patterns of PCR products of ADRB2 for the 27^th amino acid digested with ItaI. Upper panel: for hominoids. Lane 1: PCR products of a human; not digested (353 bp). Lane 2: fragments of human Gln27/Glu27 (229, 174, 97, 55 and 27 bp which was undetectable at this concentration). Lane 3: fragments of human Gln27/Gln27 (174, 97, 55 and 27 bp). Lane 4 to lane 7: fragments from P. troglodytes, G. gorilla, P. pygmaeus, and H. agilis, respectively (229 bp instead of 174 and 55 bp). Lower panel: for macaques. Lane 1: PCR products of M. mulatta; not digested (222 bp). From lane 2 to lane 6: fragments from M. mulatta, M. fuscata, M. fascicularis, M. nemestrina, and M. radiata, respectively (168 bp instead of 113 and 55 bp).

Figure 4. All NHP had Arg64 allele in ADRB3.

A) Restriction map of ADRB3 digested with MvaI for humans and NHP. B) RFLP patterns of PCR product of ADRB3 digested with MvaI for humans and NHP. Lane 1: PCR products of a human; not digested (112 bp). Lane 2: fragments of the human Trp64/Trp64 (61, 34 and 17 bp which was undetectable at this concentration.) Lane3: fragments of human Arg64/Trp64 (95, 61, 34 and 17 bp). Lane 4 to lane 12: fragments from P. troglodytes, G. gorilla, P. pygmaeus, H. agilis, M. mulatta, M. fuscata, M. fascicularis, M. nemestrina, and M. radiata, respectively (95 bp instead of 61 and 34 bp).

Figure 5. Nucleotide sequences in PPARG of primates.

The determined sequences of G. gorilla (AB669114), P. pygmaeus (AB669115), and M. fuscata (AB669116) together with the Ensembl database of human (ENSG00000132170), P. troglodytes (ENSPTRG00000014632) and M. mulatta (ENSMMUG00000007191). Underline shows the restriction site (GCGC) with HhaI. The restriction site region of M. fascicularis (AY048695) from the GenBank database was the same as in other macaques. One nucleotide of primer F was changed to create the restriction site of HhaI .

Figure 6. Summaries of effects of SNPs in ADRBs and PPARG.

A) ADRBs with energy expense-type allele found only in humans stimulate the digestion of accumulated fat in adipocytes at a higher level. A lot of generated free fatty acids (FFA) stimulate both transcription of the uncoupling protein (UCP1) gene and the activity of UCP1 proteins, which generate heat in mitochondria. GL: glycerol. B) PPARG activates differentiation from precursor cells into small-sized adipocytes, which secrete insulin-sensitive factors. PPARG with Ala12 found only in humans causes reduction of transcriptional activity of PPARG and leads to protection from high-fat-diet-induced hypertrophy of adipocytes, which secrete insulin-resistant factors , .