The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, Ags. B cells also reside and develop in the thymus, although their functions are less clear. During “thymic involution,” a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise ∼1% of human neonatal thymocytes but up to ∼10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish (Danio rerio) also have thymic B cells. In this article, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- versus postinvolution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells postinvolution. We also performed RNA sequencing on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is, to our knowledge, the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution and establishing the highly genetically manipulatable zebrafish model as a template for involution studies.

Background: Ovarian cancer is the deadliest of all gynecologic malignancies due to limited therapeutic options. Our data show that the tumor-specific metabolism of ovarian cancer could be effectively targetable, which highlights a path for new anti-cancer therapies. Methods and Results: Our work shows that the upregulation of mitochondrial enzyme SDHA is particularly prevalent in ovarian carcinoma. SDHA overexpression significantly induced orthotopic ovarian tumor growth, reducing mouse survival. We showed that SDHA-overexpressing tumors depend on glutaminolysis and increased activity of the tricarboxylic acid (TCA) cycle coupled with mitochondrial oxidative phosphorylation (OXPHOS), which are essential for high-energy metabolism and cell survival. We identified a distinctive vulnerability of SDHA-overexpressing tumors to agents targeting regulators of the OXPHOS pathway, particularly the LRPPRC protein. LRPPRC is a key regulator of mitochondrial energy metabolism, promoting OXPHOS and ATP generation. However, when overexpressed, the LRPPRC acts as a tumor oncogene. Our analysis of SDHA and LRPPRC gene and protein expression patterns in precursor lesions and established ovarian cancer demonstrated that the upregulation of SDHA is accompanied by LRPPRC overexpression, notably in advanced tumors. Our novel findings highlight for the first time a potential functional interaction between SDHA and LRPPRC in the development and progression of ovarian malignancy. Importantly, our in vivo data showed that pharmacological inhibition of LRPPRC results in a lasting therapeutic benefit and can be an effective therapy in SDHA- and LRPPRC-overexpressing ovarian tumors. Conclusions: Overall, our study underlines an understudied role of concomitant overexpression of SDHA and LRPPRC in ovarian cancer pathogenesis, highlighting new paths for therapeutic development.

Zebrafish (Danio rerio) are a compelling model for studying lymphocytes because zebrafish and humans have similar adaptive immune systems, including their lymphocytes. Antibodies that recognize zebrafish proteins are sparse, so many investigators use transgenic, lymphocyte-specific fluorophore-labeled lines. Human and zebrafish lymphocyte types are conserved, but many aspects of zebrafish lymphocyte biology remain uninvestigated, including lymphocytes in peripheral tissues, like epidermis. This study is, to our knowledge, the first study to focus on zebrafish epidermal lymphocytes, using scales. Obtaining zebrafish blood via nonlethal methods is difficult; scales represent a source to longitudinally sample live fish. We developed a novel biopsy technique, collecting scales to analyze epithelial lymphocytes from several transgenic lines. We imaged scales via confocal microscopy and demonstrated multiple lymphocyte types in scales/epidermis, quantifying them flow cytometrically. We profiled gene expression of scale, thymic, and kidney-marrow (analogous to mammalian bone marrow) lymphocytes from the same animals, revealing B- and T-lineage signatures. Single-cell quantitative real-time PCR and RNA sequencing show not only canonical B and T cells but also novel lymphocyte populations not described previously. To validate longitudinal scale biopsies, we serially sampled scales from fish treated with dexamethasone, demonstrating epidermal lymphocyte responses. To analyze cells functionally, we employed a bead-ingestion assay, showing that thymic, marrow, and epidermal lymphocytes have phagocytic activity. In summary, we establish a novel, nonlethal technique to obtain zebrafish lymphocytes, providing the first quantification, expression profiling, and functional data from zebrafish epidermal lymphocytes.

Ovarian cancer is the deadliest of all gynecologic malignancies due to limited therapeutic options. Our data show that tumor-specific metabolism of ovarian cancer could be effectively targetable, which highlights a path for new anti-cancer therapies. Our work showed that the upregulation of mitochondrial enzyme SDHA is particularly prevalent in ovarian carcinoma. The SDHA overexpression significantly induced orthotopic ovarian tumor growth substantially reducing mouse survival. We showed that the SDHA overexpressing tumors depend on glutaminolysis, and increased activity of TCA cycle coupled with mitochondrial oxidative phosphorylation (OXPHOS), which are essential for high-energy metabolism and cell survival. We also identified a distinctive vulnerability of SDHA overexpressing tumors to agents targeting regulators of OXPHOS pathway, particularly LRPPRC protein. LRPPRC is a key regulator of mitochondria homeostasis and energy metabolism promoting OXPHOS and ATP generation, however when overexpressed, the LRPPRC acts as tumor oncogene. Our analysis of SDHA and LRPPRC gene and protein expression patterns in precursor lesions and established ovarian cancer demonstrated that the upregulation of SDHA is accompanied by LRPPRC overexpression, particularly in advanced tumors. Our novel findings highlight for the first time a potential functional interaction between SDHA and LRPPRC in development and progression of ovarian malignancy. Importantly, our in vivo data showed that pharmacological blocking LRPPRC function results in a long-term therapeutic benefit and can be an effective therapy in SDHA and LRPPRC overexpressing ovarian tumors. Overall, our study underlines an understudied role of concomitant overexpression of SDHA and LRPPRC in ovarian cancer pathogenesis highlighting new opportunities for therapeutic intervention.

The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, antigens. B cells also reside and develop in the thymus, although their functions are less clear. During ‘thymic involution,’ a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise ∼1% of human neonatal thymocytes, but up to ∼10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish ( Danio rerio ) also have thymic B cells. Here, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- vs. post-involution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells post-involution. We also performed RNA sequencing (RNA-seq) on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution, and establishing the highly genetically- manipulatable zebrafish model as a template for involution studies.