MGF,
The C-terminal peptide of Mechano-Growth Factor, an alternatively spliced
variant of insulin-like growth factor 1 (IGF-1)
A strong
neuroprotective effect of the autonomous C-terminal peptide
of IGF-1 Ec (MGF) in brain ischemia
The ischemic stroke is
the third leading cause of death in developed countries.
The C-terminal peptide of mechano-growth factor (MGF),
an alternatively spliced variant of insulin-like growth
factor 1 (IGF-1), was found to function independently
from the rest of the molecule and showed a neuroprotective
effect in vivo and in vitro. In vivo, in a gerbil model
of transient brain ischemia, treatment with the synthetic
MGF C-terminal peptide provided very significant protection
to the vulnerable neurons. In the same model, ischemia
evoked increased expression of endogenous MGF in the ischemia-resistant
hippocampal neurons, suggesting that the endogenous MGF
might have an important neuroprotective function. In an
in vitro organotypic hippocampal culture model of neurodegeneration,
the synthetic peptide was as potent as the full-length
IGF-1 while its effect lasted significantly longer than
that of recombinant IGF-1. While two peptides showed an
additive effect, the neuroprotective action of the C-terminal
MGF was independent from the IGF-1 receptor, indicating
a new mode of action for this molecule. Although MGF is
known for its regenerative capability in skeletal muscle,
our findings demonstrate for the first time a neuroprotective
role against ischemia for this specific IGF-1 isoform.
Therefore, the C-terminal MGF peptide has a potential
to be developed into a therapeutic modality for the prevention
of neuronal damage.
Dluzniewska J, et al.
FASEB J. 2005 Sep 6; [Epub ahead of print]
Different roles of the IGF-I Ec peptide (MGF) and mature
IGF-I in myoblast proliferation and differentiation
The physiological function
of a recently cloned splice variant of insulin-like growth
factor-I (IGF-I; mechano growth factor (MGF)) was studied
using an in vitro cell model. Unlike mature IGF-I, the
distinct E domain of MGF inhibits terminal differentiation
whilst increasing myoblast proliferation. Blocking the
IGF-I receptor with a specific antibody indicated that
the function of MGF E domain is mediated via a different
receptor. The results provide a basis for localized tissue
adaptation and helps explain why loss of muscle mass occurs
in the elderly and in dystrophic muscle in which MGF production
is markedly affected.
Yang SY, Goldspink
G. FEBS Lett. 2002 Jul 3;522(1-3):156-60.
Figure 1. IGF-1: one gene, many proteins.
A) A schematic representation of the IGF-1 gene and its
locally produced splice variants. The black boxes denote
the insert in exon 5 (49 bp in human, 52 bp in gerbil and
other species studied), which gives rise to alternatively
spliced MGF isoform. B) The gerbil C-terminal MGF peptide
sequence shows a high degree of homology with E-domains
from other species. Based on the consensus sequence, the
C-terminal MGF peptide was synthesized. Dluzniewska J, et al.
FASEB J. 2005 Sep 6; [Epub ahead of print]
Figure 2. Representative immunoblot analysis
of the expression of endogenous MGF. The hippocampi (C-control)
and postischemic at 3, 24, 48, and 72 h after reperfusion
were divided into vulnerable (CA1) and the resistant (CA2-3,
DGabdominal, AbP) parts. Note the rapid increase and sustained
expression of MGF only in the abdominal part (arrow). There
were always two immunopositive bands present; the identity
of the larger-size band is not clear. Antibody was obtained
by immunization with synthetic C-terminal MGF peptide shown
on blots as a positive control (smaller band in MGF lane)
and does not cross-react with the recombinant IGF-1 peptide
(IGF-1 lane). Dluzniewska J, et al.
FASEB J. 2005 Sep 6; [Epub ahead of print]
Figure 3. Ischemia-induced changes in
endogenous expression of MGF in gerbil hippocampi. A–C)
In situ hybridization analysis of MGF mRNA expression.
Bright-field autoradiographs of coronal brain sections
hybridized with the MGFspecific oligo probe. The lines
outline the external margins of the hippocampal areas.
A) Control brain: very weak signal in the CA3 area of
the hippocampus. B) Six hours after ischemia: increased
MGF hybridization signal in the CA3 and the dentate gyrus
(DG). C) Negative (background) control. D) Hematoxylin
and eosin staining of the corresponding brain section
showing histological organization of the specific hippocampal
areas. E, F) Immunolocalization of the endogenous MGF
in gerbil hippocampus postischemia. Polyclonal antibody
against human (E) and rat (F) C-terminal MGF peptide was
used to stain coronal sections of gerbil brains 72 h postischemia.
E) Confocal image of MGF-specific signal visualized with
Alexa 488 (green) conjugated secondary antibody merged
with pseudo-DAPI nuclear counterstaining (×1000).
F) A single optical section from a stack of confocal images:
MGF-specific signal (green, Alexa 488) and cell nucleus
(orange, ToPro) staining. Note the MGF-specific perinuclear
reactivity with a granular appearance located in the CA3
pyramidal neurons. G) Negative (background) control in
the CA1 region. Dluzniewska J, et
al. FASEB J. 2005 Sep 6; [Epub ahead of print]
Figure 4. Neuroprotective effect of C-terminal
MGF and IGF-1 peptides in global cerebral ischemia. Histological
images of hematoxylin and eosin-stained coronal sections
of the CA1 hippocampal regions from sham-operated (A), ischemic
(B), and C-terminal MGF-treated (C) or IGF-1-treated (D)
ischemic animals analyzed 7 days after the insult. Magnifications:
×2.5 or ×10 (a–d) . Note the well-preserved
pyramidal neurones in the CA1 region in the ischemic animal
treated with C-terminal MGF peptide (Cc). Dluzniewska J, et al.
FASEB J. 2005 Sep 6; [Epub ahead of print]
Figure 5. The neuroprotective effects
of C-terminal MGF and IGF-1 peptides in vivo and in vitro.
B) Analysis in organotypic hippocampal slices. Cell damage
was quantified on fluorescence images as described in
Materials and Methods and expressed as the percentage
of maximal fluorescence (FI) produced by glutamate toxicity.
Significant differences (*P<0.001) were observed in
NMDA + Cterminal MGF peptide and NMDA + IGF-1 vs. NMDA-only
group; TBH + C-terminal MGF peptide group after 24 h and
48 h and TBH + IGF-1 group after 24 h and IgG + TBH +
C-terminal MGF peptide vs. TBH-only group. Note the additive
effect seen at 48 h of TBH + C-terminal MGF peptide +
IGF-1 vs. TBH + C-terminal MGF peptide (**P<0.001).
Columns labeled MGF and IGF-1 show the effects of these
compounds on control cultures without TBH or NMDA. Data
are presented as mean ± SD. Dluzniewska J, et
al. FASEB J. 2005 Sep 6; [Epub ahead of print]
Figure 6. The C-terminal M images (×2.5)
of propidium iodide-stained hippocampal cultures. Only
dead cells are labeled (shown in red). Peptides were added
to the culture medium at the time of insult (TBH exposure)
and were present in the medium continuously. Twenty-four
hours after insult, sections were stained with propidium
iodide, and cell viability was assessed at 24 h (A, C,
E, G, I) and 48 h (B, D, F, H, J). In control cultures,
no cell death was seen (A, B), whereas TBH exposure induced
neuronal cell death in the CA1 region (C, D). At 24 h,
both C-terminal MGF peptide (E) and IGF-1 (G) reduced
cell death. F) However, C-terminal MGF peptide protection
was longer lasting and its neuroprotective effect was
still apparent after 48 h. I, J) The protective effect
of both C-terminal MGF peptide and IGF-1 was additive.
L) The protective effect of C-terminal MGF peptide was
not mediated via the IGF-1 receptor. Specific anti-IGF-1
receptor blocking antibody was included in the culture
medium 1 h before the hippocampal slices were exposed
to TBH (K) with either 100 ng/ml of Cterminal MGF peptide
(L) or IGF-1 peptide (M). The presence of antibody significantly
reduced the protection evoked by IGF-1 but did not affect
that of C-terminal MGF peptide. Dluzniewska J, et
al. FASEB J. 2005 Sep 6; [Epub ahead of print]