Over the past five years, there have been remarkable advances in the diagnosis and therapy of LAM, including the identification of vascular endothelial growth factor D (VEGF-D) as a diagnostic biomarker and the US Food and Drug Administration approval of sirolimus as therapy for LAM.
Our findings suggest that the tissue expression levels of VEGF-D and MMP-9 are important parameters associated with the loss of pulmonary function and could be considered as potential severity markers in open lung biopsies of LAM patients.
Serum vascular endothelial growth factor-D (VEGF-D) is a lymphangiogenic growth factor that is considered a valuable tool in the diagnosis of lymphangioleiomyomatosis (LAM).
Only VEGF-D was significantly increased in LAM patients as compared with age- and gender-matched healthy volunteers (n=24) (LAM vs. control, geometric mean 95% CI; 1069.3 pg/mL (809.4 approximately 1412.6) vs. 295.9 pg/mL (262.6 approximately 333.5), p<0.0001).
By injecting TSC2-null cells into nude mice, we have developed a mouse model of LAM that is characterized by multiple random TSC2-null lung lesions, vascular endothelial growth factor-D expression, lymphangiogenesis, destruction of lung parenchyma, and decreased survival, similar to human LAM.
LAM lesions express lymphangiogenic growth factors VEGF-C and VEGF-D; growth factor receptors, VEGFR-2 and VEGFR-3; and markers LYVE-1 and podoplanin, and are laced with chaotic lymphatic channels.
As the pathogenesis of LAM is being further recognized, other therapeutic agents such as matrix metalloproteinase inhibitors, statins, interferon, VEGF inhibitors, chloroquine analogs and cyclin-dependent kinase inhibitors, along with sirolimus or a combination of several of these agents, may offer the best hope for effective therapy.
Concentration of Serum Vascular Endothelial Growth Factor (VEGF-D) and Its Correlation with Functional and Clinical Parameters in Patients with Lymphangioleiomyomatosis from a Brazilian Reference Center.
Tuberin regulates p70 S6 kinase activation and ribosomal protein S6 phosphorylation. A role for the TSC2 tumor suppressor gene in pulmonary lymphangioleiomyomatosis (LAM).
No consistent metabolic model currently exists for LAM, therefore wild-type mouse embryonic fibroblasts (MEF +/+) and TSC2 knockout cells (MEF -/-) were used in this study as a model for LAM.
In previous work we found loss of heterozygosity (LOH) of the wild-type TSC2 allele in the abnormal pulmonary smooth muscle cells and renal angiomyolipoma cells from patients with sporadic pulmonary lymphangiomyomatosis (LAM).
These data demonstrate that tuberin negatively regulates the activity of S6 and p70S6K specifically, and suggest a potential mechanism for abnormal cell growth in LAM.
Isolated pulmonary LAM cells have been difficult to maintain in culture, and most studies of LAM lung cells involve mixtures of TSC2 wild-type and TSC2-null cells.
Recent studies, however, revealed that both forms of LAM are genetically related but that sporadic LAM is a distinct clinical entity caused by somatic mutations of TSC2 (not TSC1) rather than a forme fruste of TSC carrying either of the TSC1 or TSC2 germline mutations.
The origin of LAM cells remains unknown; however, inactivation of Tsc2 gene in the mouse uterus resulted in myometrial tumors exhibiting LAM features, and approximately 50% of animals developed metastatic myometrial lung tumors.
Using a LAM patient-derived cell line (bearing biallelic Tuberin inactivation), we demonstrate that E2 stimulates a robust and biphasic activation of ERK2 and transcription of the late response-gene Fra1 associated with epithelial-to-mesenchymal transition.
Proliferation of LAM/TSC cells is epidermal growth factor (EGF)-dependent and blockade of EGF receptor causes cell death as we previously showed in cells lacking tuberin.