Intensified expressions of a monocarboxylate transporter in consistently renewing tissues of the mouse

Cell differentiation is disrupted by MYO5B loss through Wnt/Notch imbalance

Functional loss of myosin Vb (MYO5B) induces a variety of deficits in intestinal epithelial cell function and causes a congenital diarrheal disorder, microvillus inclusion disease (MVID). The impact of MYO5B loss on differentiated cell lineage choice has not been investigated. We quantified the populations of differentiated epithelial cells in tamoxifen-induced, epithelial cell–specific MYO5B-knockout (VilCre^ERT2 Myo5b^fl/fl) mice utilizing digital image analysis. Consistent with our RNA-sequencing data, MYO5B loss induced a reduction in tuft cells in vivo and in organoid cultures. Paneth cells were significantly increased by MYO5B deficiency along with expansion of the progenitor cell zone. We further investigated the effect of lysophosphatidic acid (LPA) signaling on epithelial cell differentiation. Intraperitoneal LPA significantly increased tuft cell populations in both control and MYO5B-knockout mice. Transcripts for Wnt ligands were significantly downregulated by MYO5B loss in intestinal epithelial cells, whereas Notch signaling molecules were unchanged. Additionally, treatment with the Notch inhibitor dibenzazepine (DBZ) restored the populations of secretory cells, suggesting that the Notch pathway is maintained in MYO5B-deficient intestine. MYO5B loss likely impairs progenitor cell differentiation in the small intestine in vivo and in vitro, partially mediated by Wnt/Notch imbalance. Notch inhibition and/or LPA treatment may represent an effective therapeutic approach for treatment of MVID.

Monocarboxylate transporter-1 promotes osteoblast differentiation via suppression of p53, a negative regulator of osteoblast differentiation

Monocarboxylate transporter-1 (MCT-1) is a transmembrane transporter for monocarboxylates including lactate and pyruvate. Silencing Mct1 by its small interfering RNA (siRNA) suppressed the expression of marker genes for osteoblast differentiation, namely, Tnap, Runx2, and Sp7, induced by BMP-2 in mouse myoblastic C2C12 cells. Mct1 siRNA also suppressed alkaline phosphatase activity, as well as expressions of Tnap and Bglap mRNAs in mouse primary osteoblasts. On the other hand, Mct1 siRNA did not have effects on the Smad1/5 or ERK/JNK pathways in BMP-2-stimulated C2C12 cells, while it up-regulated the mRNA expression of p53 (Trp53) as well as nuclear accumulation of p53 in C2C12 cells in a BMP-2-independent manner. Suppression of osteoblastic differentiation by Mct1 siRNA in C2C12 cells was abolished by co-transfection of Trp53 siRNA. Together, these results suggest that MCT-1 functions as a positive regulator of osteoblast differentiation via suppression of p53.

Histochemical characteristics of regressing vessels in the hyaloid vascular system of neonatal mice: Novel implication for vascular atrophy

The hyaloid vasculature constitutes a transitory system nourishing the internal structures of the developing eye, but the mechanism of vascular regression and its cell biological characteristics are not fully understood. The present study aimed to reveal the specificity of the hyaloid vessels by a systematic immunohistochemical approach for marker substances of myeloid cells and the extracellular matrix (ECM) in neonatal mice. Macrophages immunoreactive for F4/80, cathepsin D, and LYVE-1 gathered around the vasa hyaloidea propria (VHP), while small round cells in vascular lumen of VHP were selectively immunoreactive for galectin-3; their segmented nuclei and immunoreactivities for Ly-6G, CD11b, and myeloperoxidase indicated their neutrophilic origin. VHP possessed thick ECM and a dense pericyte envelope as demonstrated by immunostaining for laminin, type IV collagen, integrin β1, and NG2. The galectin-3⁺ cells loosely aggregated with numerous erythrocytes in the lumen of hyaloid vessels in a manner reminiscent of vascular congestion. Galectin-3 is known to polymerize and form a complex with ECM and NG2 as well as recruit leukocytes on the endothelium. Observation of galectin-3 KO mice implicated the involvement of galectin-3 in the regression of hyaloid vasculature. Since macrophages may play central roles including blocking of the blood flow and the induction of apoptosis in the regression, galectin-3⁺ neutrophils may play a supportive role in the macrophage-mediated involution of the hyaloid vascular system.

Immunohistochemical localization of fatty acid transporters and MCT1 in the sebaceous glands of mouse skin

The sebaceous glands secrete sebum to protect the epidermis and hairs by the oily products. The glands express several transporters and binding proteins for the production of fatty acids and uptake of their sources. The present immunohistochemical study examined the expression and localization of CD36, MCT1, FATP4, and E-FABP in the sebaceous glands, including the meibomian and preputial glands of mice. CD36 and MCT1 in sebaceous glands were largely co-localized along the plasma membrane of secretory cells, while they were separately expressed in the glandular portion of meibomian and preputial glands. Immunoreactivities for FATP4 and E-FABP appeared diffusely in the cytoplasm of secretory cells. Genetic deletion of CD36 did not affect the immunolocalization of the three other molecules. The sebaceous glands were judged to be useful for analyzing the functions and relation of fatty acid transporters and binding proteins.

Immunohistochemical localization of GLUT3, MCT1, and MCT2 in the testes of mice and rats: the use of different energy sources in spermatogenesis

Lactate represents a preferential energy substrate of germ cells rather than glucose. Testicular Sertoli cells are believed to produce lactate and pyruvate and to supply these to germ cells, particularly spermatocytes and spermatids. Monocarboxylate transporter (MCT), responsible for the transport of lactate and other monocarboxylates via the cell membrane, is abundant in the testes and sperm (MCT1, MCT2, and MCT4). For the uptake of glucose, germ cells within the seminiferous tubules and sperm have been known to intensely express GLUT3. The present study investigated expression profiles of MCTs and GLUTs and revealed their cellular and subcellular localization in the mouse and rat testis. An in situ hybridization analysis showed significant expressions of MCT1, MCT2, and GLUT3 mRNA in the testis. Immunohistochemically, spermatogonia, spermatocytes, and spermatids expressed MCT1 on their cell surfaces in a stage-dependent manner: in some seminiferous tubules, an intense expression of MCT1 was unique to the spermatogonia. MCT2 was restricted to the tails of elongated spermatids and sperm. An intense immunoreactivity for GLUT3 was shared by spermatocytes, spermatids, and sperm. Sertoli cells were devoid of any immunoreactivities for MCT1, MCT2, and GLUT3. The predominant energy source of germ cells may be lactate and other monocarboxylates--especially for spermatogonia, but glucose and other hexoses may be responsible for an energy supply to spermatocytes and spermatids.

Balancing glycolysis and mitochondrial OXPHOS: lessons from the hematopoietic system and exercising muscles

Living organisms require a constant supply of safe and efficient energy to maintain homeostasis and to allow locomotion of single cells, tissues and the entire organism. The source of energy can be glycolysis, a simple series of enzymatic reactions in the cytosol, or a much more complex process in the mitochondria, oxidative phosphorylation (OXPHOS). In this review we will examine how does the organism balance its source of energy in two seemingly distinct and unrelated processes: hematopoiesis and exercise. In both processes we will show the importance of the metabolic program and its regulation. We will also discuss the importance of oxygen availability not as a sole determinant, but in the context of the nutrient and cellular state, and address the emerging role of lactate as an energy source and signaling molecule in health and disease.

Tumor-stroma metabolic relationship based on lactate shuttle can sustain prostate cancer progression

Background

Cancer cell adopts peculiar metabolic strategies aimed to sustain the continuous proliferation in an environment characterized by relevant fluctuations in oxygen and nutrient levels. Monocarboxylate transporters MCT1 and MCT4 can drive such adaptation permitting the transport across plasma membrane of different monocarboxylic acids involved in energy metabolism.

Methods

Role of MCTs in tumor-stroma metabolic relationship was investigated in vitro and in vivo using transformed prostate epithelial cells, carcinoma cell lines and normal fibroblasts. Moreover prostate tissues from carcinoma and benign hypertrophy cases were analyzed for individuating clinical-pathological implications of MCT1 and MCT4 expression.

Results

Transformed prostate epithelial (TPE) and prostate cancer (PCa) cells express both MCT1 and MCT4 and demonstrated variable dependence on aerobic glycolysis for maintaining their proliferative rate. In glucose-restriction the presence of L-lactate determined, after 24 h of treatment, in PCa cells the up-regulation of MCT1 and of cytochrome c oxidase subunit I (COX1), and reduced the activation of AMP-activated protein kinase respect to untreated cells. The blockade of MCT1 function, performed by si RNA silencing, determined an appreciable antiproliferative effect when L-lactate was utilized as energetic fuel. Accordingly L-lactate released by high glycolytic human diploid fibroblasts WI-38 sustained survival and growth of TPE and PCa cells in low glucose culture medium. In parallel, the treatment with conditioned medium from PCa cells was sufficient to induce glycolytic metabolism in WI-38 cells, with upregulation of HIF-1a and MCT4. Co-injection of PCa cells with high glycolytic WI-38 fibroblasts determined an impressive increase in tumor growth rate in a xenograft model that was abrogated by MCT1 silencing in PCa cells. The possible interplay based on L-lactate shuttle between tumor and stroma was confirmed also in human PCa tissue where we observed a positive correlation between stromal MCT4 and tumor MCT1 expression.

Conclusions

Our data demonstrated that PCa progression may benefit of MCT1 expression in tumor cells and of MCT4 in tumor-associated stromal cells. Therefore, MCTs may result promising therapeutic targets in different phases of neoplastic transformation according to a strategy aimed to contrast the energy metabolic adaptation of PCa cells to stressful environments.