The crucial role played by hypoxia-inducible factor-1α (HIF-1α) during myogenesis has
been demonstrated in two recent publications by the proponent group (Cirillo et al.,
2017a;Cirillo et al., 2020). Specifically, it was shown that proliferating murine
myoblasts treated for 24 hours under 1% O2 (hypoxia) conditions in growth medium and then
stimulated to differentiate for 7 days under normoxic conditions (21% O2) showed the
formation of hypertrophic myotubes with a 1.4-fold increase in differentiation index
compared with normoxic controls. These results were confirmed by analysis of key
differentiation markers. Specifically, hypoxic pretreated myoblasts showed a 3-, 2.4-,
and 1.33-fold increase in MyoD nuclear localization, myogenin expression after 3 days of
differentiation, and MHC expression at the end of the differentiation process compared
with controls, respectively. Moreover, we confirmed these findings in skeletal muscle
biopsies from elderly sarcopenic patients compared with those from young individuals. We
found a decrease in the expression of HIF-1α and its target genes in sarcopenia, as well
as of PAX7, the major stem cell marker of satellite cells, whereas the atrophy marker
MURF1 was increased. We also isolated satellite cells from muscle biopsies and cultured
them in vitro. We found that a pharmacological activation of HIF-1α and its target genes
caused a reduction in skeletal muscle atrophy and activation of PAX7 gene expression. In
conclusion, in this work we found that HIF-1α plays a role in sarcopenia and is involved
in satellite cell homeostasis (Cirillo et al., 2022).
Considering our preliminary data, the first part of our project will focus on patient
recruitment and clinical characterization. Specifically, analyzes will be performed on
two separate groups: the sarcopenic group, consisting of 60 patients affected by
sarcopenia according to the most recent guidelines (> 65 years), and the control group,
consisting of 45 patients who are not sarcopenic (aged between 18 and 35 years). The
study will be conducted according to the rules of the hospital ethics committee and
patients will be required to sign an informed consent form to participate in the study.
Patients will be recruited for 24 months, with 6 months available for data analysis.
Recruitment will take place during routine orthopedic examinations at the IRCCS Istituto
Ortopedico Galeazzi in patients scheduled for orthopedic surgery (hip replacement due to
osteoarthritis, proximal femur fractures, and ALC reconstructive surgery). Patients with
comorbidities, including obesity-related sarcopenia and diabetes, will be excluded from
the study. All patients will undergo to (a) DXA total body, which allows quantification
of the three body components bone mineral, fat, and bone mineral-free mass, (b) hand-held
dynamometry to assess grip strength, and (c) anthropometric analysis (BMI) to estimate
body fat. A blood sample will be collected to determine the extent of sarcopenia by
serological analysis. This involves measuring amino-terminal pro-peptide of procollagen
type III (P3NP), c-terminal agrin fragment 22 (CAF22), osteonectin, irisin, fatty acid
binding protein 3 (FABP3), and macrophage migration inhibitory factor (MIF), which are
considered the main candidate biomarkers of sarcopenia (Nogueira et al., 2019;Qaisar et
al., 2020). Following patient recruitment, the study will aim to identify changes in
HIF-1alpha signaling during sarcopenia. Specifically, multiple skeletal muscle biopsies,
normally discarded during surgery, will be collected from sarcopenic and control groups
to set up multi-omics approaches and histological assays. In particular, total proteins
will be extracted by skeletal muscle sample to perform proteome analyzes based on mass
spectrometry and cellular bioenergetic metabolism assay using Seahorse Real-Time Cell
Metabolic Analysis in our laboratory. Statistical analysis of the proteome and metabolome
data will focus on changes in cross-talk between HIF signaling and mitochondrial
activity. The proteome results will be technically validated by a Western blot approach
using specific antibodies. Only the proteins showing a true difference in expression of
at least 0.6 will be considered. On the other hand, skeletal muscle biopsies will also be
used for histological examination. The main focus will be on 1) activation of satellite
cells by the specific antibody PAX7, 2) quantification of skeletal muscle atrophy by the
specific antibody MuRF1, 2) and changes in muscle fiber composition using specific
antibodies directed against myosin heavy chain type I, IIA, and IIB.