Ag85a/b DNA vaccine therapy improves the anabolism of
tuberculosis.
In the TB model group, most of the down-regulated DE genes were related
to cell structural proteins and cell functional proteins, and the
functional proteins of alveolar epithelial cells account for a large
proportion, such as Sftpc, Sftpb, Sftpd, Sftpa1, Mgp, Wfdc2, Sec14l3,
Postn, Cldn5, Aqp5, Emp2, Foxf1, etc. Surfactant protein A (SFTPA,
encoded by two homologous genes Sftpa1 and Sftpa2), B (SFTPB), C
(SFTPC), and D (SFTPD), secreted by alveolar epithelial cell type II,
are key elements of the innate immune system to maintain normal alveolar
structure and function and resist MTB infection(63, 64). Among them,
SFTPB and SFTPC play a role in reducing surface tension, and SFTPC also
plays an immunomodulatory role in clearing lung infection(65). SFTPA and
SFTPD are host defense lectins, which participate in the innate immune
response in the lung, and enhance the phagocytosis of macrophages on MTB
through interaction with alveolar macrophages(66, 67), thereby enhancing
microbial clearance and regulating inflammation. SFTPA and SFTPD also
regulate the functions of dendritic cells and T cells(68). Sftpa, Sftpd,
and Sftpc gene polymorphisms not only increase the risk of TB but also
may affect the host’s immune response to MTB(69). Thacker VV et al.(70)
showed that the decreased expression of alveolar epithelial cells type
II markers (Abca3, Sftpa, Sftpb, Sftpc, Sftpd) and type I markers (Aqp5
and Pdpn) would lead to the rapid growth of MTB in macrophages and
alveolar epithelial cells(71). The growth of MTB in these two cells
could be inhibited by the exogenous addition of Curosurf (surfactant
substitute of phospholipid and hydrophobic protein). Mgp, a vitamin
K-dependent inhibitor of calcification, may play an anti-inflammatory
role in monocytes and macrophages(72, 73). Claudin-5 (Cldn5), a tight
junction protein, is mainly expressed by the vascular endothelium,
especially expressed strongly in the endothelium of normal lungs(74).
The expression levels of Cldn5 were significantly decreased in various
lung diseases, such as Covid-19(75), chronic obstructive pulmonary
disease (COPD)(76), and lung injury(77), which induced damage to the
pulmonary endothelial barrier. Induction of Cldn5 expression has become
a therapeutic strategy for these diseases(77). Both our study and
GSE89403 found that MTB infection significantly reduced the expression
of Sftpd and Cldn5, but the treatment of ag85a/b DNA vaccine and
GSE89403 significantly increased the expression of Sftpd and Cldn5,
proving that Sftpd and Cldn5 can also become the targets for TB
treatment. Both our study and the GSE89839 showed that Mgp expression
decreased after MTB infection, which may affect the anti-inflammatory
effect of mice. However, after the treatment of ag85a/b DNA
vaccine and GSE89403, the expression of Mgp was significantly increased,
suggesting that the anti-inflammatory effect of mice may be improved.
The mouse Retnla (human Retn), a member of the resistin family, is a
secreted protein rich in cysteine. It is not only a protein related to
insulin resistance but also a pro-inflammatory molecule(78). Retnla is a
negative regulator of Th2-mediated pneumonia.
Retnla-/- mice developed exacerbated lung inflammation
compared with their wild-type controls(79). In this study, the
expression of Retnla was significantly down-regulated in the mouse TB
model, which was consistent with the results from two GSE data sets. In
TB patients, Retn gene expression also showed a downward trend. The
down-regulation of Retnla (Retn) expression caused Th1 immune response
to shift to Th2 immune response, while the immunotherapy of theag85a/b DNA vaccine significantly increased Retnla expression,
which was conducive to correcting Th1/Th2 immune imbalance(78). After
the immunotherapy with ag85a/b DNA vaccine IM or EP in the mice
infected with MTB, the anabolism, developmental process, and immune
response-related pathways (such as ECM receiver interaction, Focal
induction, PI3K Akt signaling pathway, Rap1 signaling pathway, etc.)
were enhanced, the transcriptional levels of the surfactant genes were
significantly up-regulated, the number of MTB colonies in the lung was
reduced, and the lung lesions in mice were alleviated, which proved that
pulmonary surfactants have a potential role in the host-directed
treatment of TB(71). The mechanism may be that surfactants can inhibit
the growth of MTB by changing the interaction between MTB and host
cells(80). In addition, surfactants can remove the virulence-related
proteins and lipids on the surface of MTB, and can wrap bacteria, so
that they are not easy to infect host cells. Therefore, ag85a/bDNA vaccine IM or EP immunization can improve the immune response,
eliminate MTB, and then correct metabolic disorders in mice.