2).ROS leads to autophagy up-regulation of ovarian endometrioma
through the TFEB-mediated mTOR independent pathway (figure).
Ovarian endometriosis is widely accepted as the direct precursor of
clear-cell and endometrioid ovarian carcinomas.(44, 45) However, when
the researchers studied the level of autophagy in ovarian endometriosis,
the results were different from endometriosis. Giulia Allavena et al.
compared LC3 and P62 expression levels in normal endometrial tissues
(NE), ovarian endometriotic cysts tissues(OMA) and eutopic endometrium
(EEOMA) groups, they found that the LC3-II and LC3-II/LC3-I ratios in
OMA were significantly higher than that in NE and EEOMA, while p62 was
significantly lower in OMA than that in NE and EEOMA.(46) Ying Ding et
al’s study shows Beclin-1 expression of ovarian granule cells was
increased and autophagy was enhanced in patients with ovarian
endometrioma.(47) researchers also found that LC3B significantly
increased expression in oviduct and ovarian endometrial epithelial
lesions compared with secretory endometrial epithelium of the control
group.(48) Serum CA125, which for the diagnosis and staging of ovarian
endometriosis, was moderately positively correlated with LC3B protein
expression.(49) All evidence is biased towards autophagy is
up-regulation in ovarian endometriosis. However, this does not conflict
with the down-regulation of autophagy observed in other areas of
endometriosis. Because the increase of autophagy level may be considered
as an integral part of the progression of endometriosis, which may
contribute to the survival and damage maintenance of ectopic endometrial
cells. Many studies indicate that oxidative stress positively associated
with the proliferation and migration of endometrial cells in the
peritoneal cavity, promoting endometriosis and infertility. Mitochondria
is major source for ROS generation.(50) It is a class of molecules
formed by incomplete reduction of oxygen, including superoxide anion
(O2•−), hydrogen peroxide (H2O2), hydroxyl radical (•OH), etc.(51) In
endometriotic cysts, bleeding can occur inside the cyst during every
menstruation cycle, so the cysts contain large amounts of free iron or
non-protein-bound iron. Subsequently, the hemoglobin from an
oxyhemoglobin state to the methemoglobin state through autoxidation and
the Fenton reaction can produce excess ROS .(52) Oxidative stress caused
by excess iron leads to uncontrolled cell growth and aberrant
intracellular signaling.(53) It has been found that TFEB is activated
under oxidative stress induced by tert-butyl peroxide or hydrogen
peroxide in nematodes.(54, 55) On the contrary, ROS elimination inhibits
TFEB activity and lysosomal function. (56-58) So the relation between
ROS and TFEB may be a mechanism for ectopic endometriosis cell
proliferation. ROS can regulate autophagy via TFEB in different ways.
ROS overproduction can lead to the activation of autophagy by
suppressing the PI3K/AKT/mTOR signaling pathway, which plays a critical
role in regulating autophagy.(59) mTOR inactivation can dissociate TFEB
from 14-3-3 and promote TFEB nuclear transposition to improve autophagy
level. However ovarian endometriotic lesions have been shown to exhibit
enhanced activation of mTOR compared with the normal endometrium.(60)
José A et al reveal the ROS inducer sodium arsenite can activate TFEB
and TFE3 without Inhibiting mTORC1 activity. This mechanism, they say,
may enable some cell types that need both TFEB/TFE3 and mTORC1
signalings, such as immune cells or cancer cells, to survive and achieve
robust cell growth in stressful conditions.(61) So there may be other
mechanisms in ovarian endometriosis that do not depend on mTOR to
control TFEB to upregulate autophagy. It was shown that under oxidative
stress situations, AMPK is activated and regulated mitophagy to relieve
intestinal ischemia/reperfusion-induced intestine disorder.(62) Abnormal
AMPK expression was observed in the endometrial microenvironment,(63)
phosphate-AMPK can activates SIRT1, SIRT1 deacetylation TFEB at K116,
enhances the expression of autophagy/lysosomal related genes, and
regulates the formation of autophagic vacuoles,(28, 64) study has found
that SIRT1 was overexpressed in endometriosis patients and may be
involved in the pathogenesis of endometriosis.(65) Moreover, Jung-yoon
Yoo et al. found that in the baboon endometriosis model, SIRT1 protein
was not significantly expressed in the endometrium of pre-inoculation
(control) baboon. However, during the progression of endometriosis,
SIRT1 protein levels increased significantly at 9 and 15 months after
inoculation.(66) Therefore, the ROS-AMPK-SIRT1-TFEB pathway may be a
mechanism for the progression of endometriosis. Besides, Izumi Suganuma
et al. discovered PGC-1a was more highly expressed in ovarian
endometrioma than in endometrium with endometriosis and normal
endometrium, and PGC-1a can promote the proliferation of ovarian
endometrioma stromal cells , whereas PGC-1a knockdown reduced the
proliferation,(67) This may be due to SIRT1-mediated deacetylation of
PGC-1a, which activates TFEB and thus induces autophagy and promotes
ectopic endometrial cell proliferation. Besides, Recent studies suggest
that the increasing level of ROS can directly activate lysosomal MCOLN1
to induce lysosomal Ca2+ release, establish a Ca2+ microdomain near the
lysosome. This leads to calcineurin activation and TFEB
dephosphorylation, which is no longer bind 14-3-3 proteins and can be
freely translocated into the nucleus, where transcriptional activation
of the lysosome/autophagy pathway occurs .(26, 68) what’s more,Hongfeng
Wang et al showed that ROS-dependent TFEB fast nuclear translocation
could occur due to oxidation of TFEB on C212 without inhibiting the
activity MTORC1.(69) Vitamin C is an antioxidant, with different doses
of vitamin C (0.5 mg, 1.25 mg and 2.5 mg), treatment of endometrial cyst
model, Durak et al Found a significant reduction in weight and volume of
cystic lesions in the 2.5 mg vitamin C group at the end of treatment,
suggesting that oxidative stress is involved in the progression of
endometriosis(70). therefore, antioxidants may be a mechanism for the
treatment of endometriosis, TFEB can be regulated by ROS through
different mechanisms, so TFEB may also be a potential target for
endometriosis treatment. What’s more, compared with both NE and EEOMA,
p53 is significantly down-regulated in OMA,(46) Study has shown that p53
deletion or the use of pifithrin-αchemical inhibition of p53 promotes
the transfer of TFEB from cytoplasm to nucleus, thereby increasing the
biogenesis of TFEB-mediated lysosomes and autophagosomes. Moreover, p53
re-expression down-regulates the TFEB target gene involved in
autophagy-lysosome pathway, while TFEB silencing eliminates the
regulatory effect of p53 on autophagy-lysosome pathway regulatory gene
transcription.(71) So TFEB inhibitors may be more effective than
antioxidants in treating endometriosis. Summary, there may be a variety
of mechanisms in ovarian endometriosis cyst to regulate TFEB. TFEB
activation and translocate into the nucleus acts on target genes, which
can promote the expression of lysosome-related proteins, thus improving
the level of autophagy of ectopic cells. High expression of TFEB and
biogenesis of lysosome are markers of poor prognosis in a quarter of
early breast cancer.(72) The expression of TFEB was positively
correlated with the malignant progression of colorectal cancer. the
tumor cells with high expression of TFEB had deeper invasion and higher
lymph node metastasis rate.(43) Whether the level of TFEB associated
with the severity of endometriosis? It requires further study.