Discussion
Osteomyelitis leads to bone infection and destruction, mainly bacterial
infection, the most common is Staphylococcus aureus, which is a major
problem in the treatment of orthopaedic diseases[22,
23]. Osteomyelitis often occurs in more serious open fractures, where
the bone fracture ends are exposed, which is easy to be invaded by
bacteria, leading to bone tissue infection or local residual bacterial
lesions[24]. Due to the destruction of skin soft
tissue and blood vessels around the bone fracture end, it is very easy
to lead to bacterial growth and bacterial biofilm adhesion, resulting in
the repeated development of clinical Osteomyelitis, which is difficult
to cure[25, 26]. At present, the clinical
treatment for chronic Osteomyelitis is mainly debridement and drainage,
and systemic sensitive antibiotics[23, 27, 28].
However, due to the poor local blood supply of the focus and the
formation of dead bones to varying degrees, the antibiotic treatment has
poor effect and large side effects[29].
As a member of MSCRAMM family, SDRC protein is mainly used to promote
the biofilm formation of Staphylococcus aureus. In Osteomyelitis
infected by Staphylococcus aureus, SDRC protein plays a huge role in the
progression and prognosis of Osteomyelitis[30]. In
our study, we constructed a model of Staphylococcus aureus induced
Osteomyelitis by knocking out the SDRC protein sequence of
Staphylococcus aureus and infecting rat, founding that compared with
wild type Staphylococcus aureus infected Osteomyelitismouse , its IL-6,
TNF- α The inflammatory indexes such as ALP, OST and RunX2 were
significantly reduced, the infection of bone tissue was significantly
lighter, and the osteogenic indexes such as ALP, OST and RunX2 were also
significantly increased, suggesting that SDRC protein played a huge role
in the occurrence and progress of Osteomyelitis infected by
Staphylococcus aureus. Previous studies[19, 31]have shown that the most important biological function of SDRC protein
is its ability to promote the formation of bacterial biofilms, which is
particularly important in the process of bacterial infection of the
host[32, 33]. Therefore, understanding the
molecular mechanism mediated by SDRC protein is of great significance
for the treatment of Staphylococcus aureus infectious diseases. Our
research results showed that after the SDRC protein is knocked out, the
biofilm forming ability of Staphylococcus aureus is significantly
weakened, and it has an invasive virulence pathogenic factor α- HL
(P=0.1868) and PSM (P=0.0361) were significantly reduced, which
confirmed that SDRC protein played an important role in the virulence of
Staphylococcus aureus, and provided a new direction for the treatment of
Staphylococcus aureus infected Osteomyelitis.
As a member of the CWA protein family, the SDRC protein mainly functions
to promote the formation of biofilms in Staphylococcus aureus through
its own dimerization, helping bacteria to proliferate on the host
surface. Derived from human neuronal cells β Axonal protein( β-
Neurexin )can interact with SDRC protein, and this interaction can
inhibit SDRC protein mediated biofilm formation, slowing down the
infection of Staphylococcus aureus to the host. In current in vivo and
in vitro experimental studies, it has been found that Staphylococcus
aureus can invade osteoblasts and cause their death. Staphylococcus
aureus, which invades osteoblasts, can also live and proliferate within
it and is believed to be related to the occurrence of chronic
osteomyelitis and recurrent osteomyelitis. In terms of bone formation,
bacterial biofilms and inflammatory cytokines inhibit the osteogenic
differentiation ability of bone marrow mesenchymal stem cells, while
Staphylococcus aureus inhibits the proliferation of osteoblasts and
induces their apoptosis.
In order to further explore the mechanism of SDRC protein promoting the
occurrence and development of Staphylococcus aureus infected
Osteomyelitis, we found that Myh7 was significantly increased in the
SDRC protein knockout group through Transcriptome sequencing, and by
constructing a stable cell line with MYH7 knockdown and functional
experiments, we found that after infection with SDRC knockout
staphylococcus, MYH7 knockdown significantly reduced its osteogenic
indicators and Ossification, compared with shNC, suggesting that MYH7
may inhibit the biological function of Staphylococcus aureus SDRC
protein. The MYH7 gene is mainly located in the long arm of chromosome
14 and contains a total of 40 exons (E1-E40)[34,
35]. It was first reported by Geisterfer Lowrance et al. in 1990. The
MYH7 gene, as the first pathogenic gene found to be associated with
hypertrophic cardiomyopathy, has been extensively reported in studies
such as myocardial injury[36]. In China, the MYH7
gene mutation range is relatively widespread in patients with
hypertrophic cardiomyopathy, except for E6, E7, E10, E17, E24, E25, E29
Pathogenic mutations are present in all 27 exons except for E32 and E33,
with 7 mutation sites located in E22[36, 37]. At
the same time, it has been found in Western populations that the most
common malignant mutations in patients with myocardial hypertrophy are
associated with R403Q, R453C, R719W, and R723G mutations in the MYH7
gene[38, 39]. In our study, we found for the first
time that MYH7 was significantly reduced in the knockout of SDRC protein
in Staphylococcus aureus osteomyelitis, indicating that MYH7 plays a
potential biological role in the occurrence and development of
Staphylococcus aureus osteomyelitis, and may have a significant
correlation with the SDRC protein of Staphylococcus aureus. This
provides a solid theoretical basis for us to further explore the deep
mechanism of SDRC protein in Staphylococcus aureus osteomyelitis in the
future.
Acknowledgements
Funding
This study was funded by National Natural Science Foundation of
China (Grant No. 82072392);
The Grants from Yunnan Orthopedics and Sports Rehabilitation
Clinical Medicine Research Center
(Grant No. 202102AA310068);
and Yunnan Prvincial Clinical Orthopaedic Trauma Medical Center
(Grant No. ZX20191001);
Clinical Key Subject Construction Project of PLA;
Medical key subject of Joint Logistic Support Force of PLA.
Author contributions
BQ, MG ,and LY conceived and designed the experiments. BQ, CM, HS, TC,
HL,
and LS performed the experiments. CL and YX analyzed the data. CL, LY,
YX
and TC contributed reagents, materials, and analysis tools. BQ and MG
wrote
the paper.
Data availability
The data of this study can be obtained from the corresponding author
upon reasonable request.
Competing interests
The authors declare no competing interests.
Ethics approval and consent to
participate
The animal experiment program was approved by the Medical Ethics
Committee of
the 920th Hospital of the PLA Joint Logistics Support Force (Approval
No: Lun
shen 2019-010 (Section) -01), and carried out in accordance with the
Guidelines
for the Care and Use of Experimental Animals.
Footnotes
These authors contributed equally: Baochuang Qi, Minzheng Guo, LiLi Yang
Contributor Information
Yongqing Xu: Email:xuyongqingkm@163.net
Chuan Li:Email:lichuankaka@163.com
Tao chen: Email:henpao@126.com