Atherosclerosis 151 2000 567 – 574
The Pro12Ala substitution in the peroxisome proliferator activated receptor gamma 2 is associated with an insulin-sensitive phenotype
in families with familial combined hyperlipidemia and in nondiabetic elderly subjects with dyslipidemia
Jussi Pihlajama¨ki
a
, Raija Miettinen
a
, Raisa Valve
a
, Leena Karjalainen
a
, Leena Mykka¨nen
a
, Johanna Kuusisto
a
, Samir Deeb
b
, Johan Auwerx
c
, Markku Laakso
a,
a
Department of Medicine, Uni6ersity of Kuopio,
70210
Kuopio, Finland
b
Departments of Medicine and Genetics, Uni6ersity of Washington, Seattle, WA, USA
c
U.
325
INSERM, De´partement d
’
Athe´roscle´rose, Institut Pasteur,
59019
Lille, France Received 27 May 1999; received in revised form 23 September 1999; accepted 13 October 1999
Abstract
Dyslipidemias and insulin resistance often present simultaneously, as in familial combined hyperlipidemia FCHL, and therefore may have a common genetic background. In our previous study the Pro12Ala substitution of peroxisome proliferator
receptor g 2 PPARg2 associated with insulin sensitivity, low body mass index BMI and high-density lipoprotein HDL cholesterol levels. In this study, we investigated the role of this substitution in dyslipidemias. Therefore, 228 nondiabetic members
of FCHL families and 866 nondiabetic elderly subjects with n = 217 and without dyslipidemia n = 649 were genotyped. The allele frequencies of the Pro12Ala substitution did not differ between elderly subjects with or without dyslipidemia or 27 probands
with FCHL. However, this substitution was associated with low fasting insulin levels both in FCHL family members P = 0.036 adjusted for gender and age and elderly subjects with dyslipidemia P = 0.050 but not in elderly subjects without dyslipidemia
P = 0.080. In addition, the Ala12 allele of PPARg2 was associated with low BMI P = 0.034 and low total triglycerides P = 0.027, and increased HDL-cholesterol P B 0.001 in elderly subjects with dyslipidemia n = 299 but not among any other
study groups. We conclude that the Ala12 isoform of PPARg2 ameliorates the insulin resistance and unfavorable lipid and lipoprotein profiles in FCHL and hyperlipidemic elderly subjects. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Familial combined hyperlipidemia; Genetics; Insulin resistance; PPARg www.elsevier.comlocateatherosclerosis
1. Introduction
Hypertriglyceridemia alone [1,2] or in combination with hypercholesterolemia [3] have been associated with
insulin resistance. In familial combined hyperlipidemia FCHL both variable dyslipidemias [4,5] and insulin
resistance [6 – 9] are often present. In FCHL patients a defect in adipose tissue metabolism has been proposed
to lead, via increased free fatty acid FFA levels both to increased hepatic lipoprotein synthesis and insulin
resistance [9 – 11]. Therefore genes that regulate fat cell metabolism are likely to be important for the under-
standing of insulin resistance in FCHL. Peroxisome
proliferator activated
receptor g
PPARg is a transcription factor belonging to the nuclear hormone receptor family that plays an impor-
tant role in adipocyte differentiation and gene expres- sion [12,13], Therefore, the PPARg gene is a potential
candidate gene both for dyslipidemias and insulin resis- tance. The PPARg gene is transcribed into three differ-
ent mRNAs [14,15], which give rise to two distinct proteins, i.e. PPARg1 and PPARg2 [16]. PPARg2 is
distinct from PPARg1 since it contains 28 additional
Corresponding author. Tel.: + 358-17-172151; fax: + 358-17- 173993.
E-mail address
:
markku.laaksouku.fi M. Laakso 0021-915000 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 0 2 1 - 9 1 5 0 9 9 0 0 4 3 3 - 5
amino acids at its NH
2
-terminus, encoded by the B exon [14 – 16]. Known natural ligands and activators of
PPARg, such as fatty acids and 15-deoxy-delta12, 14- prostaglandin J2, have a relatively low affinity for the
receptor [17,18]. In contrast, synthetic ligands, such as the antidiabetic thiazolidinediones bind with high-
affinity to PPARg [19,20], and their insulin-sensitizing effect is attributed to the activation of PPARg. In
addition to ligands, growth factors and insulin also modify PPARg activity in a ligand-independent fashion
through a MAP kinase-mediated phosphorylation of amino acids in the NH
2
-terminal activation domain [21 – 24]. Interestingly, PPARg2, which has an addi-
tional 28 amino acids at its NH
2
-terminus, is reported to be a much more effective transcriptional activator
than PPARg1 [25]. Previously we described a common Pro12Ala substi-
tution in the PPARg2-specific B exon of the PPARg gene, which was associated with a lower body mass
index BMI, higher high-density cholesterol HDL cholesterol levels in elderly subjects and improved in-
sulin sensitivity in middle-aged subjects. Accordingly, this Pro12Ala substitution decreased transcriptional ac-
tivity of PPARg [26]. Ristow et al. recently described a rare Pro115Gln mutation in the NH
2
-terminal ligand- independent activation domain. The correct position of
this mutation is likely to be Pro113Gln [15]. This mutation inhibited phosphorylation of the protein at
Ser112 and, therefore, resulted in a constitutive activa- tion of PPARg in vitro. Permanent activation of
PPARg was suggested to contribute to obesity in 4 of 121 obese subjects who carried this substitution [27].
Also, an association between a silent polymorphism in codon 453 with plasma leptin levels has been observed
in obese subjects [28]. Therefore, it appears that the activity of PPARg is directly related to adiposity and
insulin resistance.
So far no studies have specifically addressed the role of PPARg in dyslipidemias, such as FCHL. Therefore,
we evaluated the role of both the Pro12Ala and Pro115Gln substitutions in dyslipidemias and insulin
resistance in nondiabetic members n = 228 of FCHL families and in nondiabetic elderly subjects with n =
217 or without n = 649 dyslipidemia.
2. Methods
