inactivation. Confirming the importance of this mechanistically,
TGN488Imice crossed with mice overexpressing FoxO1 in the
heart display marked improvement in LVH, with full rescue of
hypertrophy when combined with rapamycin treatment
[48]. These observations highlight altered myocardial mTOR and
FoxO signalling as sufficient to account for LVH in the TGN488I
model. In addition, analysis of proliferation markers, Ki67 and
phosphohistone H3, in hearts from 2-week-old TGN488Imice has
revealed evidence of contributory cardiomyocyte proliferation at
this early stage [48].
Recently, prompted in part by concerns relating to the presence
of a phenotype in transgenic mice overexpressing WTPRKAG2
alone [49], knock-in (KI) mice designed to express more physio-
logical levels of cardiacγ2-expression have been developed and
their cardiac phenotype described [31]. The latter mice—bearing
a single mutation in either of twoγ2-residues corresponding to
human Asn488Ile or Arg531Gly (murine Asn485Ile and Arg528-
Gly, respectively)—exhibit a more subtle phenotype than the
cardiomyocyte-restricted TG mouse lines, characterized by modest
increases in cardiac mass (by age 24 weeks), upregulation in cardiac
markers of hypertrophy, and (in the case of the Arg528Gly KI)
significantly increased cardiac glycogen levels [31]. ECG assess-
ment revealed a small reduction in the PR interval (~13%) of
Arg528Gly KI mice but no significant change in QRS duration in
either KI line compared to WT control, suggesting no overt ven-
tricular pre-excitation. Taken together, these findings suggest the
presence of interspecies differences such that, in the mouse, a
genetic overexpression strategy may be required to fully recapitu-
late the more extreme cardiac phenotypes observed in humans
bearing PRKAG2 mutations, particularly ventricular
pre-excitation which may be contingent on a critical mass of glyco-
gen driven by a threshold level of mutant holoenzyme complexes.4 Impact ofPRKAG2Mutations on AMPK Activity
4.1 Insights from
In Vitro Studies
The identification of a functional role for tandem CBS motifs as
allosteric binding domains for adenine nucleotides whose mutation
could result in inherited disease [18], includingPRKAG2cardio-
myopathy, suggested thatγ2-mutations may directly impact upon
AMPK energy sensor function by disrupting its interaction withäFig. 5(continued) transgenic mice (DM); scale bar 40μm. (d) Ventricular pre-excitation is present in TGN488I
(R2M) mice, but not in double transgenic (DM) mice. (e) Heart weight/body weight ratio and (f) cardiomyocyte
cross-sectional area determined by wheat germ agglutinin staining illustrating persistence of cardiac
hypertrophy in double transgenic mice (DM); scale bar 40μm (Reproduced from ref.48 with permission
from Wolters Kluwer Health, Inc.)
596 Arash Yavari et al.