Original contributionIn situ analysis of mTORC1/2 and cellular metabolism–related proteins in human Lymphangioleiomyomatosis☆,☆☆
Introduction
Lymphangioleiomyomatosis (LAM) is a rare multisystem disorder with a strong female predilection, manifesting primarily as a progressive, diffuse cystic lung disease. Symptoms are generally due to obstructive lung disease; however, pleural complications such as pneumothorax and chylothorax may also occur. The lung cysts are related to proliferation of immature smooth muscle cells of perivascular phenotype (LAM cells) [1] and LAM is now considered as a low-grade neoplasm of the perivascular epithelioid cell tumor family [2]. The term sporadic LAM is used for patients without the tuberous sclerosis complex (TSC), while TSC-LAM refers to LAM that occurs in the setting of TSC. Both forms are primarily caused by TSC1 or TSC2 gene mutations [3]. These mutations lead to hyperactivation of the mammalian target of rapamycin (mTOR) and subsequently proliferation of LAM cells [4].
mTOR is a component of two multiprotein complexes: mTOR complex 1 and mTOR complex 2 (mTORC1 and mTORC2) (Fig. 1). In addition to mTOR, mTORC1 contains scaffold protein Raptor and mTORC2 contains scaffold protein Rictor [5]. Through its participation in mTORC1 and mTORC2, mTOR integrates a variety of environmental signals and regulates cell growth and homeostasis [6]. Activation of mTORC1 leads to phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4EBP1), S6 kinase (S6K), and ribosomal S6 protein. Phospho-S6 (p-S6) facilitates protein translation, cell growth, and proliferation. mTORC1 also influences cellular metabolism (Fig. 1). Alternatively, mTORC2 is a mediator of actin cytoskeletal organization and promotes cell survival via phosphorylation of protein kinase B and serum- and glucocorticoid-induced protein kinase [5], [6].
mTOR also plays a central role in metabolic reprogramming of neoplastic cells with altered utilization of glucose, glutamine, and lipids [5], [6], [7], [8], [9]. Increased glucose uptake and overexpression of glucose transporter 1 (GLUT1) is well documented in most neoplasms [10], [11]. Regardless, certain neoplasms, including LAM, are undetectable by positron emission tomography using 2-deoxy-2-[18F]fluoro-D-glucose [12], [13], [14], suggesting that these neoplasms may use an alternative energy source such as glutamine or acetate instead of glucose.
Sirolimus is an mTORC1 inhibitor, which has been successfully utilized to attenuate disease progression in LAM patients [15], [16]. Unfortunately, lost lung function is not restored and disease progression resumes once treatment is discontinued [16]. In addition, certain disease subgroups, such as those that are post-menopausal, may have limited if any benefit from sirolimus. Lastly, the most effective dose and treatment duration are unknown, although presumed to be lifelong. Of course, some patients are unable to tolerate the treatment due to adverse events [17], [18]. It is therefore important to identify pathobiological targets that may respond to new or additional therapeutics to mitigate the proliferation of LAM cells.
The purpose of this study was to assess the significance of mTORC1, mTORC2 and various metabolic pathways (including glycolysis, oxidative phosphorylation, glutaminolysis, fatty acid β-oxidation, and acetate utilization) in the pathogenesis of LAM, using semiquantitative immunohistochemical methods on formalin-fixed paraffin-embedded human lung tissue.
Section snippets
Tissues
Our study was approved by the Mayo Clinic Institutional Review Board. Formalin-fixed paraffin-embedded lung tissue was available from the lung tissue registry for 11 patients with sporadic LAM. These patients underwent lung transplantation (7 patients) and diagnostic wedge biopsies (4 patients) at Mayo Clinic in Jacksonville, Florida, between January 1, 2004 and December 31, 2016. Diagnosis of LAM was based on the presence of characteristic clinical, radiologic, and histologic findings and was
Expression of LAM cell markers
Expression of LAM cell markers and hormone receptors are shown in Table 3. LAM cells were positive for HMB-45 in 9 of 11 cases (82%). All cases were positive for SMA and β-catenin.
Expression of mTOR-related proteins
In LAM cells, high p-S6 expression suggesting high mTORC1 activity was observed in 10 of 11 cases (91%), and high Rictor expression suggesting high mTORC2 activity was observed in 6 of 11 cases (55%) (Fig. 3). Low expression for both p-S6 and Rictor was observed in only 1 case. In contrast, no or low expression was
Discussion
Histologically, LAM is characterized by cystic spaces surrounded by bundles of proliferating LAM-type smooth muscle cells [20]. These LAM cells are typically immunoreactive for HMB-45, β-catenin, SMA, desmin, ER, and progesterone receptor [21], [22], [23], [24].
mTOR plays an important role in the regulation of protein translation, cell growth, proliferation, cytoskeletal organization, and cellular metabolism [5], [8], [9] (Fig. 1). In this study, expression of p-S6 (downstream target of mTORC1)
References (35)
- et al.
The 2015 World Health Organization classification of lung tumors: impact of genetic, clinical and radiologic advances since the 2004 classification
J Thorac Oncol
(2015) - et al.
Evidence that lymphangiomyomatosis is caused by TSC2 mutations: chromosome 16p13 loss of heterozygosity in angiomyolipomas and lymph nodes from women with lymphangiomyomatosis
Am J Hum Genet
(1998) - et al.
Lymphangioleiomyomatosis (LAM): molecular insights lead to targeted therapies
Respir Med
(2010) - et al.
The mechanistic target of rapamycin: the grand ConducTOR of metabolism and aging
Cell Metab
(2016) - et al.
mTOR signaling in growth, metabolism, and disease
Cell
(2017) - et al.
Utility of [18F]2-fluoro-2-deoxyglucose-PET in sporadic and tuberous sclerosis-associated lymphangioleiomyomatosis
Chest
(2009) - et al.
Intracrine steroid production and mammalian target of rapamycin pathways in pulmonary lymphangioleiomyomatosis
Hum Pathol
(2015) - et al.
Bronchial involvement in advanced stage lymphangioleiomyomatosis: histopathologic and molecular analyses
Hum Pathol
(2016) - et al.
Acetate dependence of tumors
Cell
(2014) - et al.
The mTORC1 pathway stimulates glutamine metabolism and cell proliferation by repressing SIRT4
Cell
(2013)
The mTORC1/S6K1 pathway regulates glutamine metabolism through the eIF4B-dependent control of c-Myc translation
Curr Biol
European Respiratory Society guidelines for the diagnosis and management of lymphangioleiomyomatosis
Eur Respir J
Fundamentals of cancer metabolism
Sci Adv
Therapeutic targeting of cellular metabolism in cells with hyperactive mTORC1: a paradigm shift
Mol Cancer Res
Making new contacts: the mTOR network in metabolism and signalling crosstalk
Nat Rev Mol Cell Biol
Potential role of sugar transporters in cancer and their relationship with anticancer therapy
Int J Endocrinol
Targeting glucose metabolism for cancer therapy
J Exp Med
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Disclosures/Conflict of Interest: none.
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Funding/Support: This work was supported by the ÚNKP-17-3 New National Excellence Program of The Ministry of Human Capacities (I. K.), scientific grant of the Hungarian Respiratory Foundation (I. K.), Bolyai Fellowship of Hungarian Academy of Sciences (A. S.), and Semmelweis University Innovation Found STIA-KF-17 (A. S.).
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These authors contributed equally to this work.