Characterization of the Pathogenesis of Lymphangioleiomyomatosis (LAM)

National Heart, Lung, And Blood Institute

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Abstract

A.Clinical and molecular effects of mTOR inhibitors: Patients with LAM and TSC are frequently treated with oral mTOR inhibitors. Sirolimus therapy of patients with LAM and TSC resulted in shrinkage of AMLs and stabilization of lung function, but discontinuation of sirolimus led to reversal of these effects. To investigate the consequences of intermittent exposure to sirolimus, we used an in vitro system with TSC2-null skin tumor cells. TSC2 deficiency increased cell volume whereas sirolimus reduced the volume of TSC2-/- cells. Sirolimus suppressed proliferation of TSC2+/-and TSC2-/- fibroblasts. Withdrawal of sirolimus from TSC2-/- cells resulted in a highly proliferative phenotype and caused cells to enter the S-phase of the cell cycle, with persistent phosphorylation of mTOR, p70 S6 kinase, ribosomal protein S6, and 4EBP1, decreased cyclin D kinase inhibitors and transient hyperactivation of Akt. Since our data demonstrated that TSC2-/- cells continued to grow at a low rate even in the presence of sirolimus and proliferate more rapidly after withdrawal of sirolimus, it would be reasonable to consider combination of sirolimus with other drugs in clinical trials. We documented the frequency of adverse cutaneous effects in TSC patients taking oral mTOR inhibitors. Twenty-three of 30 individuals with LAM and TSC were treated with oral sirolimus (median dose:2 mg/day, range:1-9 mg/day) and seven with oral everolimus (median dose: 5 mg/day, range:2-10 mg/day). Median duration of therapy was 5 years (range:0.5-15 years). For those taking sirolimus, median trough serum level was 7.2 ng/mL (range:2-34 ng/mL). Twenty-nine individuals (97%) presented with or reported modifications of the skin, soft tissues, mucous membranes, nails, or hair within one month to nine years following initiation of therapy. The most common dermatologic side effects, each of which occurred in over half of patients, were oral ulceration and acneiform eruptions. Nearly half of the patients developed hand or lower extremity edema. Eight (27%) individuals experienced impaired wound healing following injury or surgery, including two with slow healing following skin biopsies, one who developed thigh seromas after a motor vehicle accident, and one who developed an abdominal wall seroma following surgery. Eight (27%) individuals experienced folliculitis; of these, two eventually developed furunculosis and one developed cellulitis requiring oral antibiotic treatment. Herpes zoster virus and tinea infection occurred in two individuals each. All side effects were grade 1 or 2 severity except for one individual who had to discontinue sirolimus treatment due to painful oral ulcers (grade 3). Overall, we found that dermatologic side effects of oral mTOR inhibitors are common but generally do not necessitate treatment discontinuation. B. Recognition of the manifestations of TSC: One of our goals has been to facilitate the diagnosis of TSC by improving recognition of TSC skin findings. By compiling our observations from detailed clinical and pathological evaluations over several years, we have identified skin findings that are either under-recognized or previously unknown, and have documented characteristic pathological features to assist in lesion identification. In the past 2 years we have published our observations regarding military fibromas (MiF), fibrous cephalic plaques (FCPs), and hair pigmentary changes. We characterized the clinical and pathological features of MiF in individuals with TSC. MiF were observed in 19 of 133 (14%) individuals with TSC. MiF were 1 to 3 mm skin-colored, sessile papules scattered on the back and rarely buttocks or thighs. Histological features of MiF included expansion of the papillary and periadnexal dermis with variable hamartomatous abnormalities involving adjacent epithelial components. MiF are distinct from other cutaneous lesions in TSC, e.g., shagreen patches, angiofibromas. Recognition of this entity is important in defining the spectrum of TSC disease and reassuring individuals with TSC that these lesions are benign. FCPs may be excised for cosmetic reasons or biopsied to confirm lesion identification and TSC diagnosis. Seventy-six lesions were observed in 36/119 individuals. Erythematous lesions were more commonly found on the forehead, face, or neck than the scalp (OR=12.6, p=0.0001). In samples of 21 lesions, thickened and disorganized collagen fiber bundles were present in 95% (20/21). Perifollicular fibrosis was observed in 95% (20/21), enhanced vascularity in 52% (11/21), and features of fibrofolliculoma in 43% (9/21) of lesions. Other abnormalities included features similar to trichofolliculoma, follicular-derived, infundibular-type cysts, and abnormally arranged primitive hair follicles. FCPs in TSC exhibit thickened bundles of collagen and hamartomatous changes involving hair follicles. Recognition of these histopathological features may raise the possibility of unsuspected TSC or confirm FCP identification. Poliosis is a white patch of hair that occurs in infancy in about 20% of individuals with TSC. Several individuals with TSC in our LAM cohort reported premature graying, so we investigated the frequency and clinical characteristics of hair pigmentary changes in TSC. Seven of 26 (27%) patients with TSC reported onset of hair graying 25 years, at a median age of 21 years (range 9-25). Infancy or childhood-onset poliosis was reported by 6/26 (23%) patients, four of whom reported spontaneous repigmentation in adolescence or adulthood. Hair graying in TSC is distinct from poliosis; it generally occurs later in childhood, is progressive, and shows gray hairs interspersed among pigmented hairs rather than sharply demarcated patches with decreased pigmentation. C. Mosaicism in TSC: We continue to explore the spectrum of mosaic TSC. We identified clinical clues of low-level mosaicism including unilateral or asymmetric distribution of facial angiofibromas (AFs) and disease penetrance in adulthood. Based on these observations, we developed a clinical diagnostic algorithm to guide patient evaluation. Phenotypes suggestive of germline TSC included onset of ungual fibromas (UFs) before age 15 years (PPV=92%, 11/12 patients, CI: 0.61-1.0), AFs before age 5 years (77%, 10/13, 0.46-0.95), and the presence of 3 mucocutaneous findings plus subependymal nodules (SENs) (71%, 20/28, 0.51-0.87). Phenotypes suggestive of mosaicism included the presence of < 3 mucocutaneous findings (PPV=88%, 7/8 patients, CI: 0.47-1.0), absence of tubers and SENs (100%, 3/3, 0.29-1.0), and asymmetrically distributed AFs with < 100 lesions (100%, 7/7, 0.59-1.0). Individuals with these phenotypes fell into the group consisting of mostly low-level mosaic TSC. The blood VAF of mosaic individuals within this group was < 1% in 6/9 individuals. In contrast, 15/19 of their skin tumor samples had a VAF >1%. Thus, the first step of their genetic workup should include NGS of TSC-related tumors. Once a pathogenic variant is identified, targeted sequencing methods such as amplicon NGS can be used to assess variant prevalence in other tissues (e.g., blood, urine, saliva, normal skin, skin tumor, internal tumor), to confirm the variant as mosaic rather than a second hit somatic mutation. In conclusion, we propose a stepwise clinical algorithm applicable to adults with TSC that provides guidance for an efficient approach to TSC gene pathogenic variant identification and identify those most likely to have mosaicism. D. COVID 19-related studies: LAM and TSC patients may be treated with mTOR inhibitors, which are immunosuppressive drugs. We are currently comparing the vaccination responses of patients being treated or not being treated with these drugs by comparing the levels of anti-Spike protein antibodies.