Cytoskeletal β-tubulin and cysteine cathepsin L deregulation by SARS-CoV-2 spike protein interaction with the neuronal model cell line SH-SY5Y

SARS-CoV-2 mainly infects the respiratory tract but can also target other organs, including the central nervous system. While it was recently shown that cells of the blood-brain-barrier are permissive to SARS-CoV-2 infection in vitro, it remains debated whether neurons can be infected. In this study, we demonstrate that vesicular stomatitis virus particles pseudotyped with the spike protein of SARS-CoV-2 variants WT, Alpha, Delta and Omicron enter the neuronal model cell line SH-SY5Y. Cell biological analyses of the pseudo-virus treated cultures showed marked alterations in microtubules of SH-SY5Y cells. Because the changes in β-tubulin occurred in most cells, but only few were infected, we further asked whether interaction of the cells with spike protein might be sufficient to cause molecular and structural changes. For this, SH-SY5Y cells were incubated with trimeric spike proteins for time intervals of up to 24 h. CellProfiler™-based image analyses revealed changes in the intensities of microtubule staining in spike protein-incubated cells. Furthermore, expression of the spike protein-processing protease cathepsin L was found to be up-regulated by wild type, Alpha and Delta spike protein pseudotypes and cathepsin L was found to be secreted from spike protein-treated cells. We conclude that the mere interaction of the SARS-CoV-2 with neuronal cells can affect cellular architecture and proteolytic capacities. The molecular mechanisms underlying SARS-CoV-2 spike protein induced cytoskeletal changes in neuronal cells remain elusive and require future studies.

Cathepsin V regulates cell cycle progression and histone stability in the nucleus of breast cancer cells

Introduction: We previously identified that Cathepsin V (CTSV) expression is associated with poor prognosis in ER+ breast cancer, particularly within the Luminal A subtype. Examination of the molecular role of the protease within Luminal A tumours, revealed that CTSV promotes tumour cell invasion and proliferation, in addition to degradation of the luminal transcription factor, GATA3, via the proteasome. Methods: Cell line models expressing CTSV shRNA or transfected to overexpress CTSV were used to examine the impact of CTSV on cell proliferation by MTT assay and flow cytometry. Western blotting analysis was used to identify the impact of CTSV on histone and chaperone protein expression. Cell fractionation and confocal microscopy was used to illustrate the presence of CTSV in the nuclear compartment. Results: In this work we have identified that CTSV has an impact on breast cancer cell proliferation, with CTSV depleted cells exhibiting delayed progression through the G2/M phase of the cell cycle. Further investigation has revealed that CTSV can control nuclear expression levels of histones H3 and H4 via regulating protein expression of their chaperone sNASP. We have discovered that CTSV is localised to the nuclear compartment in breast tumour cells, mediated by a bipartite nuclear localisation signal (NLS) within the CTSV sequence and that nuclear CTSV is required for cell cycle progression and histone stability in breast tumour cells. Discussion: Collectively these findings support the hypothesis that targeting CTSV may have utility as a novel therapeutic target in ER+ breast cancer by impairing cell cycle progression via manipulating histone stabilisation.

Metallacarborane Cluster Anions of the Cobalt Bisdicarbollide-Type as Chaotropic Carriers for Transmembrane and Intracellular Delivery of Cationic Peptides

Cobalt bisdicarbollides (COSANs) are inorganic boron-based anions that have been previously reported to permeate by themselves through lipid bilayer membranes, a propensity that is related to their superchaotropic character. We now introduce their use as selective and efficient molecular carriers of otherwise impermeable hydrophilic oligopeptides through both artificial and cellular membranes, without causing membrane lysis or poration at low micromolar carrier concentrations. COSANs transport not only arginine-rich but also lysine-rich peptides, whereas low-molecular-weight analytes such as amino acids as well as neutral and anionic cargos (phalloidin and BSA) are not transported. In addition to the unsubstituted isomers (known as ortho- and meta-COSAN), four derivatives bearing organic substituents or halogen atoms have been evaluated, and all six of them surpass established carriers such as pyrenebutyrate in terms of activity. U-tube experiments and black lipid membrane conductance measurements establish that the transport across model membranes is mediated by a molecular carrier mechanism. Transport experiments in living cells showed that a fluorescent peptide cargo, FITC-Arg₈, is delivered into the cytosol.

Investigations on Primary Cilia of Nthy-ori 3-1 Cells upon Cysteine Cathepsin Inhibition or Thyrotropin Stimulation

In the thyroid gland, cysteine cathepsins are secreted upon thyrotropin stimulation for thyroglobulin processing, and they are present at the primary cilia of thyroid epithelial cells. Treatment with protease inhibitors resulted in the loss of cilia from rodent thyrocytes and caused redistribution of the thyroid co-regulating G protein-coupled receptor Taar1 to the endoplasmic reticulum. These findings suggest that ciliary cysteine cathepsins are important to maintain sensory and signaling properties for the proper regulation and homeostasis of thyroid follicles. Therefore, it is important to better understand how cilia structure and frequencies are maintained in human thyroid epithelial cells. Hence, we aimed to investigate the potential role of cysteine cathepsins for the maintenance of primary cilia in the normal human Nthy-ori 3-1 thyroid cell line. This was approached by determining cilia lengths and frequencies in cysteine peptidase inhibition conditions in Nthy-ori 3-1 cell cultures. Cilia lengths were shortened upon 5 h of cysteine peptidase inhibition with cell-impermeable E64. Likewise, cilia lengths and frequencies were decreased upon additional overnight treatment with the cysteine peptidase-targeting, activity-based probe DCG-04. The results suggest that cysteine cathepsin activity is required for the maintenance of the cellular protrusions not only in rodents, but also in human thyrocytes. Hence, thyrotropin stimulation was used to simulate physiological conditions that eventually lead to cathepsin-mediated thyroglobulin proteolysis, which is initiated in the thyroid follicle lumen. Immunoblotting revealed that thyrotropin stimulation conditions result in the secretion of little procathepsin L and some pro- and mature cathepsin S but no cathepsin B from the human Nthy-ori 3-1 cells. Unexpectedly, however, 24 h incubation periods with thyrotropin shortened the cilia although higher amounts of cysteine cathepsins were present in the conditioned media. These data point to the necessity of further studies to delineate which of the cysteine cathepsins plays the most prominent role in cilia shortening and/or elongation. Collectively, the results of our study provide corroboration for the hypothesis of thyroid autoregulation by local mechanisms that our group previously proposed.

Lack of L-type amino acid transporter 2 in murine thyroid tissue induces autophagy

Proteolytic cleavage of thyroglobulin (Tg) for thyroid hormone (TH) liberation is followed by TH release from thyroid follicles into the circulation, enabled by TH transporters. The existence of a functional link between Tg-processing cathepsin proteases and TH transporters has been shown to be independent of the hypothalamus-pituitary-thyroid axis. Thus, lack of cathepsin K, combined with genetic defects in the TH transporters Mct8 and Mct10, that is the Ctsk-/-/Mct8-/y/Mct10-/- genotype, results in persistent Tg proteolysis due to autophagy induction. Because amino acid transport by L-type amino acid transporter 2 (Lat2) has been described to regulate autophagy, we asked whether Lat2 availability is affected in Ctsk-/-/Mct8-/y/Mct10-/- thyroid glands. Our data revealed that while mRNA amounts and subcellular localization of Lat2 remained unaltered in thyroid tissue of Ctsk-/-/Mct8-/y/Mct10-/- mice in comparison to WT controls, the Lat2 protein amounts were significantly reduced. These data suggest a direct link between Lat2 function and autophagy induction in Ctsk-/-/Mct8-/y/Mct10-/- mice. Indeed, thyroid tissue of Lat2-/- mice showed enhanced endo-lysosomal cathepsin activities, increased autophagosome formation, and enhanced autophagic flux. Collectively, these results suggest a mechanistic link between insufficient Lat2 protein function and autophagy induction in the thyroid gland of male mice.

Age-dependent response to T4 overtreatment and recovery on systemic and organ level

Thyroid hormone (TH) metabolism and cellular TH action are influenced by ageing. To investigate the response to thyroxine (T4) overtreatment, a kinetic study was conducted in young and aged mice with chronic hyperthyroidism and hormone withdrawal. Five and 22 months old male mice were treated with T4 or PBS over 5 weeks, followed by observation for up to 12 days. Serial analysis was performed for thyroid function parameters, transcript levels of TH target genes, deiodinase type 1 (DIO1) activity as well as serum lipids at 12, 24, 72, 144, 216, and 288 h after cessation of T4 administration. Higher FT3 concentrations and higher renal DIO1 activities were noted in aged mice 12 h after T4 withdrawal and marked thyroid-stimulating hormone elevation was found in aged mice after 12 days compared to respective controls. A biphasic expression pattern occurred for TH target genes in all organs and a hypothyroid organ state was observed at the end of the study, despite normalization of TH serum concentrations after 72 h. In line with this, mirror-image kinetics were detected for serum cholesterol and triglycerides in aged and young mice. Recovery from TH overtreatment in mice involves short- and medium-term adaption of TH metabolism on systemic and organ levels. Increased renal DIO1 activity may contribute to higher T3 concentrations and prolonged thyrotoxicosis followed by hypothyroidism in an aged-mouse organism. Translation of these findings in the clinical setting seems warranted and may lead to better management of hyperthyroidism and prevention of T4 overtreatment in aged patients.

Trace Amine-Associated Receptor 1 Trafficking to Cilia of Thyroid Epithelial Cells

Trace amine-associated receptor 1 (rodent Taar1/human TAAR1) is a G protein-coupled receptor that is mainly recognized for its functions in neuromodulation. Previous in vitro studies suggested that Taar1 may signal from intracellular compartments. However, we have shown Taar1 to localize apically and on ciliary extensions in rodent thyrocytes, suggesting that at least in the thyroid, Taar1 may signal from the cilia at the apical plasma membrane domain of thyrocytes in situ, where it is exposed to the content of the follicle lumen containing putative Taar1 ligands. This study was designed to explore mouse Taar1 (mTaar1) trafficking, heterologously expressed in human and rat thyroid cell lines in order to establish an in vitro system in which Taar1 signaling from the cell surface can be studied in future. The results showed that chimeric mTaar1-EGFP traffics to the apical cell surface and localizes particularly to spherical structures of polarized thyroid cells, procilia, and primary cilia upon serum-starvation. Moreover, mTaar1-EGFP appears to form high molecular mass forms, possibly homodimers and tetramers, in stably expressing human thyroid cell lines. However, only monomeric mTaar1-EGFP was cell surface biotinylated in polarized human thyrocytes. In polarized rat thyrocytes, mTaar1-EGFP is retained in the endoplasmic reticulum, while cilia were reached by mTaar1-EGFP transiently co-expressed in combination with an HA-tagged construct of the related mTaar5. We conclude that Taar1 trafficking to cilia depends on their integrity. The results further suggest that an in vitro cell model was established that recapitulates Taar1 trafficking in thyrocytes in situ, in principle, and will enable studying Taar1 signaling in future, thus extending our general understanding of its potential significance for thyroid autoregulation.

The Amino Acid Transporter Mct10/Tat1 Is Important to Maintain the TSH Receptor at Its Canonical Basolateral Localization and Assures Regular Turnover of Thyroid Follicle Cells in Male Mice

Cathepsin K-mediated thyroglobulin proteolysis contributes to thyroid hormone (TH) liberation, while TH transporters like Mct8 and Mct10 ensure TH release from thyroid follicles into the blood circulation. Thus, thyroid stimulating hormone (TSH) released upon TH demand binds to TSH receptors of thyrocytes, where it triggers Gαq-mediated short-term effects like cathepsin-mediated thyroglobulin utilization, and Gαs-mediated long-term signaling responses like thyroglobulin biosynthesis and thyrocyte proliferation. As reported recently, mice lacking Mct8 and Mct10 on a cathepsin K-deficient background exhibit excessive thyroglobulin proteolysis hinting towards altered TSH receptor signaling. Indeed, a combination of canonical basolateral and non-canonical vesicular TSH receptor localization was observed in Ctsk-/-/Mct8-/y/Mct10-/- mice, which implies prolonged Gαs-mediated signaling since endo-lysosomal down-regulation of the TSH receptor was not detected. Inspection of single knockout genotypes revealed that the TSH receptor localizes basolaterally in Ctsk-/- and Mct8-/y mice, whereas its localization is restricted to vesicles in Mct10-/- thyrocytes. The additional lack of cathepsin K reverses this effect, because Ctsk-/-/Mct10-/- mice display TSH receptors basolaterally, thereby indicating that cathepsin K and Mct10 contribute to TSH receptor homeostasis by maintaining its canonical localization in thyrocytes. Moreover, Mct10-/- mice displayed reduced numbers of dead thyrocytes, while their thyroid gland morphology was comparable to wild-type controls. In contrast, Mct8-/y, Mct8-/y/Mct10-/-, and Ctsk-/-/Mct8-/y/Mct10-/- mice showed enlarged thyroid follicles and increased cell death, indicating that Mct8 deficiency results in altered thyroid morphology. We conclude that vesicular TSH receptor localization does not result in different thyroid tissue architecture; however, Mct10 deficiency possibly modulates TSH receptor signaling for regulating thyrocyte survival.

The Thyroid Hormone Transporter Mct8 Restricts Cathepsin-Mediated Thyroglobulin Processing in Male Mice through Thyroid Auto-Regulatory Mechanisms That Encompass Autophagy

The thyroid gland is both a thyroid hormone (TH) generating as well as a TH responsive organ. It is hence crucial that cathepsin-mediated proteolytic cleavage of the precursor thyroglobulin is regulated and integrated with the subsequent export of TH into the blood circulation, which is enabled by TH transporters such as monocarboxylate transporters Mct8 and Mct10. Previously, we showed that cathepsin K-deficient mice exhibit the phenomenon of functional compensation through cathepsin L upregulation, which is independent of the canonical hypothalamus-pituitary-thyroid axis, thus, due to auto-regulation. Since these animals also feature enhanced Mct8 expression, we aimed to understand if TH transporters are part of the thyroid auto-regulatory mechanisms. Therefore, we analyzed phenotypic differences in thyroid function arising from combined cathepsin K and TH transporter deficiencies, i.e., in Ctsk^-/-/Mct10^-/-, Ctsk^-/-/Mct8^-/y, and Ctsk^-/-/Mct8^-/y/Mct10^-/-. Despite the impaired TH export, thyroglobulin degradation was enhanced in the mice lacking Mct8, particularly in the triple-deficient genotype, due to increased cathepsin amounts and enhanced cysteine peptidase activities, leading to ongoing thyroglobulin proteolysis for TH liberation, eventually causing self-thyrotoxic thyroid states. The increased cathepsin amounts were a consequence of autophagy-mediated lysosomal biogenesis that is possibly triggered due to the stress accompanying intrathyroidal TH accumulation, in particular in the Ctsk^-/-/Mct8^-/y/Mct10^-/- animals. Collectively, our data points to the notion that the absence of cathepsin K and Mct8 leads to excessive thyroglobulin degradation and TH liberation in a non-classical pathway of thyroid auto-regulation.

Mice Hypomorphic for Keap1, a Negative Regulator of the Nrf2 Antioxidant Response, Show Age-Dependent Diffuse Goiter with Elevated Thyrotropin Levels

Background: Familial nontoxic multinodular goiter (MNG) is a rare disease. One of the associated genes is Kelch-like ECH-associated protein 1 (KEAP1), which encodes the main inhibitor of nuclear factor erythroid 2-related transcription factor 2 (Nrf2), a central mediator of antioxidant responses. The association of KEAP1 with familial MNG is based on only two loss-of-function mutations identified in two families, only one of which included proper phenotyping and adequate demonstration of co-segregation of the phenotype and the mutation. There is no experimental evidence from model organisms to support that decreased Keap1 levels can, indeed, cause goiter. This study used mice hypomorphic for Keap1 to test whether decreased Keap1 expression can cause goiter, and to characterize the activation status of Nrf2 in their thyroid. Methods: C57BL/6J Keap1flox/flox (Keap1 knock-down [Keap1KD]) mice were studied at 3 and 12 months of age. Plasma and thyroid glands were harvested for evaluation of thyroid function tests and for gene and protein expression by real-time polymerase chain reaction and immunoblotting, respectively. Results: Keap1KD mice showed diffuse goiter that began to develop in early adult life and became highly prominent and penetrant with age. The goiter was characterized by a markedly increased size of thyroid follicles, most notably of the colloid compartment, and by absence of thyroid nodules or hyperplasia. Keap1KD mice also showed decreased T4 levels in early adult life that were eventually well compensated over time by increased thyrotropin (TSH) levels. Nrf2 was activated in the thyroid of Keap1KD mice. Despite a known stimulatory effect of Nrf2 on thyroglobulin (Tg) gene transcription and Tg protein abundance, the expression levels were decreased in the thyroid of Keap1KD mice. No clear patterns were observed in the expression profiles of other thyroid hormone synthesis-specific factors, with the exception of Tg-processing and Tg-degrading cathepsins, including an increase in mature forms of cathepsins D, L, and S. Conclusions: Keap1KD mice develop age-dependent diffuse goiter with elevated TSH levels. The precise mechanism accounting for the thyroidal phenotype remains to be elucidated, but it may involve enhanced Tg solubilization and excessive lysosomal Tg degradation.

Significance of nuclear cathepsin V in normal thyroid epithelial and carcinoma cells

Altered expression and/or localization of cysteine cathepsins is believed to involve in thyroid diseases including cancer. Here, we examined the localization of cathepsins B and V in human thyroid tissue sections of different pathological conditions by immunolabeling and morphometry. Cathepsin B was mostly found within endo-lysosomes as expected. In contrast, cathepsin V was detected within nuclei, predominantly in cells of cold nodules, follicular and papillary thyroid carcinoma tissue, while it was less often detected in this unusual localization in hot nodules and goiter tissue. To understand the significance of nuclear cathepsin V in thyroid cells, this study aimed to establish a cellular model of stable nuclear cathepsin V expression. As representative of a specific form lacking the signal peptide and part of the propeptide, N-terminally truncated cathepsin V fused to eGFP recapitulated the nuclear localization of endogenous cathepsin V throughout the cell cycle in Nthy-ori 3-1 cells. Interestingly, the N-terminally truncated cathepsin V-eGFP was more abundant in the nuclei during S phase. These findings suggested a possible contribution of nuclear cathepsin V forms to cell cycle progression. Indeed, we found that N-terminally truncated cathepsin V-eGFP expressing cells were more proliferative than those expressing full-length cathepsin V-eGFP or wild type controls. We conclude that a specific molecular form of cathepsin V localizes to the nucleus of thyroid epithelial and carcinoma cells, where it might involve in deregulated pathways leading to hyperproliferation. These findings highlight the necessity to better understand cathepsin trafficking in health and disease. In particular, cell type specificity of mislocalization of cysteine cathepsins, which otherwise act in a functionally redundant manner, seems to be important to understand their non-canonical roles in cell cycle progression.

Aging Alters Phenotypic Traits of Thyroid Dysfunction in Male Mice With Divergent Effects on Complex Systems but Preserved Thyroid Hormone Action in Target Organs

Clinical manifestation of hyperthyroidism and hypothyroidism vary with age, with an attenuated, oligosymptomatic presentation of thyroid dysfunction (TD) in older patients. We asked, whether in rodents TD phenotypes are influenced by age and whether this involves changes in systemic and/or organ thyroid hormone (TH) signaling. Chronic hyper- or hypothyroidism was induced in male mice at different life stages (5, 12, and 20 months). TH excess resulted in pronounced age-specific body weight changes (increase in youngest and decrease in old mice), neither explained by changes in food intake (similar increase at all ages), nor by thermogenic gene expression in brown adipose tissue (BAT) or TH serum concentrations. Relative increase in body temperature and activity were more pronounced in old compared to young hyperthyroid mice. An attenuated hypothyroid state was found in old mice for locomotor activity and in heart and BAT on functional (less bradycardia) and gene expression level (heart and BAT). In contrast, decrease in body weight was pronounced in old hypothyroid mice. Thus, age has divergent impact on features of TD in mice, whereby effects on highly complex systems, such as energy homeostasis are not proportional to serum TH state, in contrast to organ-specific responses in heart and BAT.

OR28-01 Constitutive Activation of NRF2 Antioxidant Response Leads to Age-Dependent Goiter and Compensated Hypothyroidism in Male Mice

Background: Familial non-toxic multinodular goiter (MNG) is a rare disease. KEAP1 gene (Kelch-like ECH-associated protein 1) that encodes the main inhibitor of nuclear factor erythroid 2-related transcription factor 2 (Nrf2), a central mediator of antioxidant responses, has been found to be one of the mutated genes that lead to familial MNG. The proposed association of KEAP1 with familial MNG is based on only two loss-of-function mutations in respective Japanese families, only one of which included proper phenotyping and demonstration of co-segregation of phenotype and mutation. To date, there is no experimental evidence from model organisms to support that decreased Keap1 levels can cause goiter. Hypothesis: We hypothesized that enhanced Nrf2 signaling induced by loss of Keap1 function in mice can lead to goiter. Methods: To this end, male Keap1 hypomorphic C57BL/6J mice that express ~80% less Keap1 in their tissues (Keap1 knockdown mice:“Keap1KD”) were studied at 3 and 12 months of age and compared to wild-type mice (WT). Plasma, thyroids and pituitary glands were collected for assessment of thyroid function by radioimmunoassays and for histology as well as gene and protein expression by quantitative PCR and immunoblotting respectively. Results: Keap1KD showed diffuse goiter that began to develop in early adult life and became highly prominent at the age of 12 months when the thyroids of Keap1KD were 6-fold heavier than WT. Histomorphometry assessment of thyroids showed that Keap1KD had ~3-fold larger follicle area and colloid compartment but no thyroid nodules or hyperplasia was detected. Keap1KD also showed primary hypothyroidism already in early adult life that was eventually well-compensated over time by increased TSH levels (at age of 12 months: WT TSH=47.7±9.1 mU/L, Keap1KD TSH=460±74 mU/L). This was also reflected in the pituitary gland of Keap1KD where Tshb mRNA was ~3-fold higher than WT. Despite a known stimulatory effect of Nrf2 on Tg gene transcription and Tg protein abundance, these measures were decreased in the thyroid of Keap1KD mice. No clear patterns were observed in the expression profiles of other thyroid hormone synthesis-specific factors, such as Duox1, Duoxa1, Duox2, Duoxa2, Tpo, Nis, Dio1, Dio2, Dehal1 mRNA levels, with the exception of Tg-processing and Tg-degrading cathepsins, including an increase in mature forms of cathepsins D, L and S. Conclusions: Keap1KD mice showed age-dependent diffuse goiter and compensated hypothyroidism. The precise mechanism accounting for the thyroidal phenotype remains to be elucidated, but it may involve enhanced Tg solubilization and excessive lysosomal Tg degradation. This study unravels novel roles of the druggable Keap1/Nrf2 pathway in thyroid function and economy. Subclinical hypothyroidism in Keap1KD mice may have broader implications regarding their use in metabolic research.

Auto-Regulation of the Thyroid Gland Beyond Classical Pathways

This mini-review asks how self-regulation of the thyroid gland is realized at the cellular and molecular levels by canonical and non-canonical means. Canonical pathways of thyroid regulation comprise thyroid stimulating hormone-triggered receptor signaling. As part of non-canonical regulation, we hypothesized an interplay between protease-mediated thyroglobulin processing and thyroid hormone release into the circulation by means of thyroid hormone transporters like Mct8. We proposed a sensing mechanism by different thyroid hormone transporters, present in specific subcellular locations of thyroid epithelial cells, selectively monitoring individual steps of thyroglobulin processing, and thus, the cellular thyroid hormone status. Indeed, we found that proteases and thyroid hormone transporters are functionally inter-connected, however, in a counter-intuitive manner fostering self-thyrotoxicity in particular in Mct8- and/or Mct10-deficient mice. Furthermore, the possible role of the G protein-coupled receptor Taar1 is discussed, because we detected Taar1 at cilia of the apical plasma membrane of thyrocytes in vitro and in situ. Eventually, through pheno-typing Taar1-deficient mice, we identified a co-regulatory role of Taar1 and the thyroid stimulating hormone receptors. Recently, we showed that inhibition of thyroglobulin-processing enzymes results in disappearance of cilia from the apical pole of thyrocytes, while Taar1 is re-located to the endoplasmic reticulum. This pathway features a connection between thyrotropin-stimulated secretion of proteases into the thyroid follicle lumen and substrate-mediated self-assisted control of initially peri-cellular thyroglobulin processing, before its reinternalization by endocytosis, followed by extensive endo-lysosomal liberation of thyroid hormones, which are then released from thyroid follicles by means of thyroid hormone transporters.

Function of Cathepsin K in the Central Nervous System of Male Mice is Independent of Its Role in the Thyroid Gland

Cathepsin K deficiency in male mice (Ctsk^-/-) results in decreased numbers of hippocampal astrocytes and altered neuronal patterning as well as learning and memory deficits. Additionally, cathepsin K carries essential roles in the thyroid gland where it contributes to the liberation of thyroid hormones (TH). Because TH are essential for brain development, in particular for the cerebellum, we investigated whether cathepsin K's function in the thyroid is directly linked to the brain phenotype of Ctsk^-/- mice. Serum levels of thyroid stimulating hormone, brain concentrations of free TH, and deiodinase 2 (Dio2) activity in brain parenchyma as well as cerebellar development were comparable in Ctsk^-/- and WT animals, suggesting regular thyroid states and TH metabolism. Despite unaltered transcript levels, protein expression of two TH transporters was enhanced in specific brain regions in Ctsk^-/- mice, suggesting altered TH supply to these regions. Thyrotropin releasing hormone (Trh) mRNA levels were enhanced threefold in the hippocampus of Ctsk^-/- mice. In the striatum of Ctsk^-/- mice the mRNA for Dio2 and hairless were approximately 1.3-fold enhanced, while mRNA levels for monocarboxylate transporter 8 and Trh were reduced to 60% and 40%, respectively, pointing to altered striatal physiology. We conclude that the role of cathepsin K in the thyroid gland is not directly associated with its function in the central nervous system (CNS) of mice. Future studies will show whether the brain region-specific alterations in Trh mRNA may eventually result in altered neuroprotection that could explain the neurobehavioral defects of Ctsk^-/- mice.

Treatment of rat thyrocytes in vitro with cathepsin B and L inhibitors results in disruption of primary cilia leading to redistribution of the trace amine associated receptor 1 to the endoplasmic reticulum

Taar1 is a G protein-coupled receptor (GPCR) confined to primary cilia of rodent thyroid epithelial cells. Taar1-deficient mouse thyroid follicles feature luminal accumulation of thyroglobulin suggesting that Taar1 acts as a regulator of extra- and pericellular thyroglobulin processing, which is mediated by cysteine cathepsin proteases present at the apical plasma membrane of rodent thyrocytes. Here, by immunostaining and confocal laser scanning microscopy, we demonstrated co-localization of cathepsin L, but only little cathepsin B, with Taar1 at primary cilia of rat thyrocytes, the FRT cells. Because proteases were shown to affect half-lives of certain receptors, we determined the effect of cathepsin activity inhibition on sub-cellular localization of Taar1 in FRT cells, whereupon Taar1 localization altered such that it was retained in compartments of the secretory pathway. Since the same effect on Taar1 localization was observed in both cathepsin B and L inhibitor-treated cells, the interaction of cathepsin activities and sub-cellular localization of Taar1 was thought to be indirect. Indeed, we observed that cathepsin inhibition resulted in a lack of primary cilia from FRT cells. Next, we proved that primary cilia are a necessity for Taar1 trafficking to reach the plasma membrane of FRT cells, since the disruption of primary cilia by treatment with β-cyclodextrin resulted in Taar1 retention in compartments of the secretory pathway. Furthermore, in less well-polarized rat thyrocytes, namely in FRTL-5 cells lacking primary cilia, Taar1 was mainly confined to the compartments of the secretory pathway. We conclude that Taar1 localization in polarized thyroid epithelial cells requires the presence of primary cilia, which is dependent on the proteolytic activity of cysteine cathepsins B and L.

Evidence of G-protein-coupled receptor and substrate transporter heteromerization at a single molecule level

G-protein-coupled receptors (GPCRs) can constitute complexes with non-GPCR integral membrane proteins, while such interaction has not been demonstrated at a single molecule level so far. We here investigated the potential interaction between the thyrotropin receptor (TSHR) and the monocarboxylate transporter 8 (MCT8), a member of the major facilitator superfamily (MFS), using fluorescence cross-correlation spectroscopy (FCCS). Both the proteins are expressed endogenously on the basolateral plasma membrane of the thyrocytes and are involved in stimulation of thyroid hormone production and release. Indeed, we demonstrate strong interaction between both the proteins which causes a suppressed activation of Gq/11 by TSH-stimulated TSHR. Thus, we provide not only evidence for a novel interaction between the TSHR and MCT8, but could also prove this interaction on a single molecule level. Moreover, this interaction forces biased signaling at the TSHR. These results are of general interest for both the GPCR and the MFS research fields.

Canonical TSH Regulation of Cathepsin-Mediated Thyroglobulin Processing in the Thyroid Gland of Male Mice Requires Taar1 Expression

Trace amine-associated receptor 1 (Taar1) has been suggested as putative receptor of thyronamines. These are aminergic messengers with potential metabolic and neurological effects countering their contingent precursors, the thyroid hormones (THs). Recently, we found Taar1 to be localized at the primary cilia of rodent thyroid epithelial cells in vitro and in situ. Thus, Taar1 is present in a location of thyroid follicles where it might be involved in regulation of cathepsin-mediated proteolytic processing of thyroglobulin, and consequently TH synthesis. In this study, taar1 knock-out male mice (taar1^-/-) were used to determine whether Taar1 function would entail differential alterations in thyroid states of young and adult animals. Analyses of blood serum revealed unaltered T₄ and T₃ concentrations and unaltered T₃-over-T₄ ratios upon Taar1 deficiency accompanied, however, by elevated TSH concentrations. Interestingly, TSH receptors, typically localized at the basolateral plasma membrane domain of wild type controls, were located at vesicular membranes in thyrocytes of taar1^-/- mice. In addition, determination of epithelial extensions in taar1^-/- thyroids showed prismatic cells, which might indicate activation states higher than in the wild type. While gross degradation of thyroglobulin was comparable to controls, deregulated thyroglobulin turnover in taar1^-/- mice was indicated by luminal accumulation of covalently cross-linked thyroglobulin storage forms. These findings were in line with decreased proteolytic activities of thyroglobulin-solubilizing and -processing proteases, due to upregulated cystatins acting as their endogenous inhibitors in situ. In conclusion, Taar1-deficient mice are hyperthyrotropinemic in the absence of respective signs of primary hypothyroidism such as changes in body weight or TH concentrations in blood serum. Thyrocytes of taar1^-/- mice are characterized by non-canonical TSH receptor localization in intracellular compartments, which is accompanied by altered thyroglobulin turnover due to a disbalanced proteolytic network. These finding are of significance considering the rising popularity of using TAAR1 agonists or antagonists as neuromodulating pharmacological drugs. Our study highlights the importance of further evaluating potential off-target effects regarding TSH receptor mislocalization and the thyroglobulin processing machinery, which may not only affect the TH-generating thyroid gland, but may emanate to other TH target organs like the CNS dependent on their proper supply.

Differential regulation of monocarboxylate transporter 8 expression in thyroid cancer and hyperthyroidism

OBJECTIVE

Thyroid hormone (TH) transporters are expressed in thyrocytes and most play a role in TH release. We asked whether expression of the monocarboxylate transporter 8 (MCT8) and the L-type amino acid transporters LAT2 and LAT4 is changed with thyrocyte dedifferentiation and in hyperfunctioning thyroid tissues.

DESIGN AND METHODS

Protein expression and localization of transporters was determined by immunohistochemistry in human thyroid specimen including normal thyroid tissue (NT, n = 19), follicular adenoma (FA, n = 44), follicular thyroid carcinoma (FTC, n = 45), papillary thyroid carcinoma (PTC, n = 40), anaplastic thyroid carcinoma (ATC, n = 40) and Graves' disease (GD, n = 50) by calculating the 'hybrid' (H) score. Regulation of transporter expression was investigated in the rat follicular thyroid cell line PCCL3 under basal and thyroid stimulating hormone (TSH) conditions.

RESULTS

MCT8 and LAT4 were localized at the plasma membrane, while LAT2 transporter showed cytoplasmic localization. MCT8 expression was downregulated in benign and malignant thyroid tumours as compared to NT. In contrast, significant upregulation of MCT8, LAT2 and LAT4 was found in GD. Furthermore, a stronger expression of MCT8 was demonstrated in PCCL3 cells after TSH stimulation.

CONCLUSIONS

Downregulation of MCT8 in thyroid cancers qualifies MCT8 as a marker of thyroid differentiation. The more variable expression of LATs in distinct thyroid malignancies may be linked with other transporter properties relevant to altered metabolism in cancer cells, i.e. amino acid transport. Consistent upregulation of MCT8 in GD is in line with increased TH release in hyperthyroidism, an assumption supported by our in vitro results showing TSH-dependent upregulation of MCT8.

Metabolome Comparison of Bioactive and Inactive Rhododendron Extracts and Identification of an Antibacterial Cannabinoid(s) from Rhododendron collettianum

INTRODUCTION

The science of metabolomics offers the possibility to measure full secondary plant metabolomes with limited experimental effort to allow identification of metabolome differences using principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of liquid chromatography mass spectrometry (LC-MS) data.

OBJECTIVE

To demonstrate a bioinformatics driven hypothesis generator for identification of biologically active compounds in plant crude extracts, which is validated by activity guided fractionation.

METHODOLOGY

Crude extracts of Rhododendron leaves were tested for their antibacterial activity using agar diffusion and minimum inhibitory concentration assays. Extracts were profiled by LC-MS. PCA and PLS-DA were used for differentiation of bioactive and inactive extracts and their metabolites. Preparative-high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy were used for separation and structure elucidation of pure compound(s) respectively.

RESULTS

An antibacterial Rhododendron collettianum was compared to a series of inactive extracts. Three metabolites were found to distinguish R. collettianum from other species indicating the ability of PCA and PLS-DA to suggest potential bioactive substances. An activity-guided fractionation of R. collettianum extracts was carried out and cannabiorcichromenic acid (CCA) was identified as antibacterial compound thereby validating the PCA and PLS-DA generated hypothesis. Four mammalian cell lines were used to estimate possible cytotoxicity of CCA.

CONCLUSION

It was shown that bioinformatics tools facilitate early stage identification of a biologically active compound(s) using LC-MS data, which reduce complexity and number of separation steps in bioactive screening. Copyright © 2017 John Wiley & Sons, Ltd.

Interdependence of thyroglobulin processing and thyroid hormone export in the mouse thyroid gland

Thyroid hormone (TH) target cells need to adopt mechanisms to maintain sufficient levels of TH to ensure regular functions. This includes thyroid epithelial cells, which generate TH in addition to being TH-responsive. However, the cellular and molecular pathways underlying thyroid auto-regulation are insufficiently understood. In order to investigate whether thyroglobulin processing and TH export are sensed by thyrocytes, we inactivated thyroglobulin-processing cathepsins and TH-exporting monocarboxylate transporters (Mct) in the mouse. The states of thyroglobulin storage and its protease-mediated processing and degradation were related to the levels of TH transporter molecules by immunoblotting and immunofluorescence microscopy. Thyroid epithelial cells of cathepsin-deficient mice showed increased Mct8 protein levels at the basolateral plasma membrane domains when compared to wild type controls. While the protein amounts of the thyroglobulin-degrading cathepsin D remained largely unaffected by Mct8 or Mct10 single-deficiencies, a significant increase in the amounts of the thyroglobulin-processing cathepsins B and L was detectable in particular in Mct8/Mct10 double deficiency. In addition, it was observed that larger endo-lysosomes containing cathepsins B, D, and L were typical for Mct8- and/or Mct10-deficient mouse thyroid epithelial cells. These data support the notion of a crosstalk between TH transporters and thyroglobulin-processing proteases in thyroid epithelial cells. We conclude that a defect in exporting thyroxine from thyroid follicles feeds back positively on its cathepsin-mediated proteolytic liberation from the precursor thyroglobulin, thereby adding to the development of auto-thyrotoxic states in Mct8 and/or Mct10 deficiencies. The data suggest TH sensing molecules within thyrocytes that contribute to thyroid auto-regulation.

Bioactivity in Rhododendron: A Systemic Analysis of Antimicrobial and Cytotoxic Activities and Their Phylogenetic and Phytochemical Origins

The exceptional diversity of the genus Rhododendron has a strong potential for identification, characterization, and production of bioactive lead compounds for health purposes. A particularly relevant field of application is the search for new antibiotics. Here, we present a comparative analysis of nearly 90 Rhododendron species targeted toward the search for such candidate substances. Through a combination of phytochemical profiles with antimicrobial susceptibility and cytotoxicity, complemented by phylogenetic analyses, we identify seven potentially antimicrobial active but non-cytotoxic compounds in terms of mass-to-charge ratios and retention times. Exemplary bioactivity-guided fractionation for a promising Rhododendron species experimentally supports in fact one of these candidate lead compounds. By combining categorical correlation analysis with Boolean operations, we have been able to investigate the origin of bioactive effects in further detail. Intriguingly, we discovered clear indications of systems effects (synergistic interactions and functional redundancies of compounds) in the manifestation of antimicrobial activities in this plant genus.

Efficacy of protocols for induction of chronic hyperthyroidism in male and female mice

Protocols for induction of hyperthyroidism in mice are highly variable and mostly involve short-term thyroid hormone (TH) treatment. In addition, little is known about a possible influence of sex on experimental TH manipulation. Here we analyzed the efficacy of intraperitoneal vs. oral levothyroxine (T4) administration to induce chronic hyperthyroidism in male and female mice and asked which T4 dosing intervals are required to achieve stable organ thyrotoxicosis. T4 was administered intraperitoneally or orally over a period of 6/7 weeks. Assessment included monitoring of body weight, TH serum concentrations, and serial quantitative TH target gene expression analysis in liver and heart. Our results show that both intraperitoneal and oral T4 treatment are reliable methods for induction of chronic hyperthyroidism in mice. Thereby T4 injection intervals should not exceed 48 h and oral levothyroxine should be administered continuously during experiments and up to sacrifice to ensure a hyperthyroid organ state. Furthermore, we found a sex-dependent variation in levothyroxine-induced TH serum state, with significantly higher T4 concentrations in female mice, while expression of investigated classical TH responsive genes in liver and heart did not vary with animal's sex. In summary, our study shows that common approaches for rendering rodents thyrotoxic can also be used for induction of chronic hyperthyroidism in male and female mice. Thereby T4 dosing intervals are critical as are read-out parameters to verify a chronic thyrotoxic organ state.

Construction of a plasmid coding for green fluorescent protein tagged cathepsin L and data on expression in colorectal carcinoma cells

The endo-lysosomal cysteine cathepsin L has recently been shown to have moonlighting activities in that its unexpected nuclear localization in colorectal carcinoma cells is involved in cell cycle progression (Tamhane et al., 2015) [1]. Here, we show data on the construction and sequence of a plasmid coding for human cathepsin L tagged with an enhanced green fluorescent protein (phCL-EGFP) in which the fluorescent protein is covalently attached to the C-terminus of the protease. The plasmid was used for transfection of HCT116 colorectal carcinoma cells, while data from non-transfected and pEGFP-N1-transfected cells is also shown. Immunoblotting data of lysates from non-transfected controls and HCT116 cells transfected with pEGFP-N1 and phCL-EGFP, showed stable expression of cathepsin L-enhanced green fluorescent protein chimeras, while endogenous cathepsin L protein amounts exceed those of hCL-EGFP chimeras. An effect of phCL-EGFP expression on proliferation and metabolic states of HCT116 cells at 24 h post-transfection was observed.

Assessment of cytotoxicity exerted by leaf extracts from plants of the genus Rhododendron towards epidermal keratinocytes and intestine epithelial cells

Background

Rhododendron leaf extracts were previously found to exert antimicrobial activities against a range of Gram-positive bacteria. In this study, we investigated which of the extracts with these antimicrobial properties would be best suited for further exploitation. Specifically, the project aims to identify biologically active compounds that affect bacterial but not mammalian cells when applied in medical treatments such as lotions for ectopic application onto skin, or as orally administered drugs.

Methods

Different concentrations of DMSO-dissolved remnants of crude methanol Rhododendron leaf extracts were incubated for 24 h with cultured epidermal keratinocytes (human HaCaT cell line) and epithelial cells of the intestinal mucosa (rat IEC6 cell line) and tested for their cytotoxic potential. In particular, the cytotoxic potencies of the compounds contained in antimicrobial Rhododendron leaf extracts were assessed by quantifying their effects on (i) plasma membrane integrity, (ii) cell viability and proliferation rates, (iii) cellular metabolism, (iv) cytoskeletal architecture, and (v) determining initiation of cell death pathways by morphological and biochemical means.

Results

Extracts of almost all Rhododendron species, when applied at 500 μg/mL, were potent in negatively affecting both keratinocytes and intestine epithelial cells, except material from R. hippophaeoides var. hippophaeoides. Extracts of R. minus and R. racemosum were non-toxic towards both mammalian cell types when used at 50 μg/mL, which was equivalent to their minimal inhibitory concentration against bacteria. At this concentration, leaf extracts from three other highly potent antimicrobial Rhododendron species proved non-cytotoxic against one or the other mammalian cell type: Extracts of R. ferrugineum were non-toxic towards IEC6 cells, and extracts of R. rubiginosum as well as R. concinnum did not affect HaCaT cells. In general, keratinocytes proved more resistant than intestine epithelial cells against the treatment with compounds contained in Rhododendron leaf extracts.

Conclusions

We conclude that leaf extracts from highly potent antimicrobial R. minus and R. racemosum are safe to use at 50 μg/mL in 24-h incubations with HaCaT keratinocytes and IEC6 intestine epithelial cells in monolayer cultures. Extracts from R. rubiginosum as well as R. concinnum or R. ferrugineum are applicable to either keratinocytes or intestinal epithelial cells, respectively. Beyond the scope of the current study, further experiments are required to identify the specific compounds contained in those Rhododendron leaf extracts that exert antimicrobial activity while being non-cytotoxic when applied onto human skin or gastrointestinal tract mucosa. Thus, this study supports the notion that detailed phytochemical profiling and compound identification is needed for characterization of the leaf extracts from specific Rhododendron species in order to exploit their components as supplementary agents in antimicrobial phyto-medical treatments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0860-8) contains supplementary material, which is available to authorized users.

Nuclear cathepsin L activity is required for cell cycle progression of colorectal carcinoma cells

Prominent tasks of cysteine cathepsins involve endo-lysosomal proteolysis and turnover of extracellular matrix constituents or plasma membrane proteins for maintenance of intestinal homeostasis. Here we report on enhanced levels and altered subcellular localization of distinct cysteine cathepsins in adenocarcinoma tissue in comparison to adjacent normal colon. Immunofluorescence and immunoblotting investigations revealed the presence of cathepsin L in the nuclear compartment in addition to its expected endo-lysosomal localization in colorectal carcinoma cells. Cathepsin L was represented as the full-length protein in the nuclei of HCT116 cells from which stefin B, a potent cathepsin L inhibitor, was absent. Fluorescence activated cell sorting analyses with synchronized cell cultures revealed deceleration of cell cycle progression of HCT116 cells upon inhibition of cathepsin L activity, while expression of cathepsin L-enhanced green fluorescent protein chimeras accelerated S-phase entry. We conclude that the activity of cathepsin L is high in the nucleus of colorectal carcinoma cells because of lacking stefin B inhibitory activity. Furthermore, we hypothesize that nuclear cathepsin L accelerates cell cycle progression of HCT116 cells thereby supporting the notion that cysteine cathepsins may play significant roles in carcinogenesis due to deregulated trafficking.

Differences in Mouse Hepatic Thyroid Hormone Transporter Expression with Age and Hyperthyroidism

BACKGROUND

Clinical features of thyroid dysfunction vary with age, and an oligosymptomatic presentation of hyperthyroidism is frequently observed in the elderly. This suggests age modulation of thyroid hormone (TH) action, which may occur, for example, by alterations in TH production, metabolism and/or TH action in target organs.

OBJECTIVES

In this paper, we address possible changes in TH transporter expression in liver tissues as a mechanism of age-dependent variation in TH action.

METHODS

Chronic hyperthyroidism was induced in 4- and 20-month-old C57BL6/NTac male mice (n = 8-10) by intraperitoneal injections of 1 µg/g body weight L-thyroxine (T4) every 48 h over 7 weeks. Control animals were injected with PBS. Total RNA was isolated from liver samples for analysis of the TH transporter and TH-responsive gene expression. TH concentrations were determined in mice sera.

RESULTS

Baseline serum free T4 (fT4) concentrations were significantly higher in euthyroid young compared to old mice. T4 treatment increased total T4, fT4 and free triiodothyronine to comparable concentrations in young and old mice. In the euthyroid state, TH transporter expression was significantly higher in old than in young mice, except for Mct8 and Oatp1a1 expression levels. Hyperthyroidism resulted in upregulation of Mct10, Lat1 and Lat2 in liver tissue, while Oatp1a1, Oatp1b2 and Oatp1a4 expression was downregulated. This effect was preserved in old animals.

CONCLUSION

Here, we show age-dependent differences in TH transporter mRNA expression in the euthyroid and hyperthyroid state of mice focusing on the liver as a classical TH target organ.

Trace Amine-Associated Receptor 1 Localization at the Apical Plasma Membrane Domain of Fisher Rat Thyroid Epithelial Cells Is Confined to Cilia

BACKGROUND

The trace amine-associated receptor 1 (Taar1) is one member of the Taar family of G-protein-coupled receptors (GPCR) accepting various biogenic amines as ligands. It has been proposed that Taar1 mediates rapid, membrane-initiated effects of thyronamines, the endogenous decarboxylated and deiodinated relatives of the classical thyroid hormones T4 and T3.

OBJECTIVES

Although the physiological actions of thyronamines in general and 3-iodothyronamine (T1AM) in particular are incompletely understood, studies published to date suggest that synthetic T1AM-activated Taar1 signaling antagonizes thyromimetic effects exerted by T3. However, the location of Taar1 is currently unknown.

METHODS

To fill this gap in our knowledge we employed immunofluorescence microscopy and a polyclonal antibody to detect Taar1 protein expression in thyroid tissue from Fisher rats, wild-type and taar1-deficient mice, and in the polarized FRT cells.

RESULTS

With this approach we found that Taar1 is expressed in the membranes of subcellular compartments of the secretory pathway and on the apical plasma membrane of FRT cells. Three-dimensional analyses further revealed Taar1 immunoreactivity in cilial extensions of postconfluent FRT cell cultures that had formed follicle-like structures.

CONCLUSIONS

The results suggest Taar1 transport along the secretory pathway and its accumulation in the primary cilium of thyrocytes. These findings are of significance considering the increasing interest in the role of cilia in harboring functional GPCR. We hypothesize that thyronamines can reach and activate Taar1 in thyroid follicular epithelia by acting from within the thyroid follicle lumen, their potential site of synthesis, as part of a nonclassical mechanism of thyroid autoregulation.

Understanding the Healthy Thyroid State in 2015

Thyroid hormones (TH) are of crucial importance for the physiological function of almost all organs. In cases of abnormal TH signaling, pathophysiological consequences may arise. The routine assessment of a healthy or diseased thyroid function state is currently based on the determination of serum concentrations of thyroid-stimulating hormone (TSH), and the TH T3 and T4. However, the definition of a 'normal' TSH range and similarly 'normal' T3 and T4 concentrations remains the subject of debate in different countries worldwide and has important implications on patient treatment in clinics. Not surprisingly, a significant number of patients whose thyroid function tests are biochemically determined to be within the normal range complain of impaired well-being. The reasons for this are so far not fully understood, but it has been recognized that thyroid function status needs to be 'individualized' and extended beyond simple TSH measurement. Thus, more precise and reliable parameters are required in order to optimally define the healthy thyroid status of an individual, and as a perspective to employ these in clinical routine. With the recent identification of new key players in TH action, a more accurate assessment of a patient's thyroid status may in the future become possible. Recently described distinct TH derivatives and metabolites, TH transporters, nongenomic TH effects (either through membrane-bound or cytosolic signaling), and classical nuclear TH action allow for insights into molecular and cellular preconditions of a healthy thyroid state. This will be a prerequisite to improve management of thyroid dysfunction, and additionally to prevent and target TH-related nonthyroid disease.

Proteolysis mediated by cysteine cathepsins and legumain-recent advances and cell biological challenges

Proteases play essential roles in protein degradation, protein processing, and extracellular matrix remodeling in all cell types and tissues. They are also involved in protein turnover for maintenance of homeostasis and protein activation or inactivation for cell signaling. Proteases range in function and specificity, with some performing distinct substrate cleavages, while others accomplish proteolysis of a wide range of substrates. As such, different cell types use specialized molecular mechanisms to regulate the localization of proteases and their function within the compartments to which they are destined. Here, we focus on the cysteine family of cathepsin proteases and legumain, which act predominately within the endo-lysosomal pathway. In particular, recent knowledge on cysteine cathepsins and their primary regulator legumain is scrutinized in terms of their trafficking to endo-lysosomal compartments and other less recognized cellular locations. We further explore the mechanisms that regulate these processes and point to pathological cases which arise from detours taken by these proteases. Moreover, the emerging biological roles of specific forms and variants of cysteine cathepsins and legumain are discussed. These may be decisive, pathogenic, or even deadly when localizing to unusual cellular compartments in their enzymatically active form, because they may exert unexpected effects by alternative substrate cleavage. Hence, we propose future perspectives for addressing the actions of cysteine cathepsins and legumain as well as their specific forms and variants. The increasing knowledge in non-canonical aspects of cysteine cathepsin- and legumain-mediated proteolysis may prove valuable for developing new strategies to utilize these versatile proteases in therapeutic approaches.

Phylogenetic spectrum and analysis of antibacterial activities of leaf extracts from plants of the genus Rhododendron

BACKGROUND

Plants are traditionally used for medicinal treatment of numerous human disorders including infectious diseases caused by microorganisms. Due to the increasing resistance of many pathogens to commonly used antimicrobial agents, there is an urgent need for novel antimicrobial compounds. Plants of the genus Rhododendron belong to the woody representatives of the family Ericaceae, which are typically used in a range of ethno-medical applications. There are more than one thousand Rhododendron species worldwide. The Rhododendron-Park Bremen grows plants representing approximately 600 of the known Rhododendron species, and thus enables research involving almost two thirds of all known Rhododendron species.

METHODS

Twenty-six bacterial species representing different taxonomic clades have been used to study the antimicrobial potential of Rhododendron leaf extracts. Agar diffusion assay were conducted using 80% methanol crude extracts derived from 120 Rhododendron species. Data were analyzed using principal component analysis and the plant-borne antibacterial activities grouped according the first and second principal components.

RESULTS

The leaf extracts of 17 Rhododendron species exhibited significant growth-inhibiting activities against Gram-positive bacteria. In contrast, only very few of the leaf extracts affected the growth of Gram-negative bacteria. All leaf extracts with antimicrobial bioactivity were extracted from representatives of the subgenus Rhododendron, with 15 from the sub-section Rhododendron and two belonging to the section Pogonanthum. The use of bacterial multidrug efflux pump mutants revealed remarkable differences in the susceptibility towards Rhododendron leaf extract treatment.

CONCLUSIONS

For the first time, our comprehensive study demonstrated that compounds with antimicrobial activities accumulate in the leaves of certain Rhododendron species, which mainly belong to a particular subgenus. The results suggested that common genetic traits are responsible for the production of bioactive secondary metabolite(s) which act primarily on Gram-positive organisms, and which may affect Gram-negative bacteria in dependence of the activity of multidrug efflux pumps in their cell envelope.

Modulation of monocarboxylate transporter 8 oligomerization by specific pathogenic mutations

The monocarboxylate transporter 8 (MCT8) is a member of the major facilitator superfamily (MFS). These membrane-spanning proteins facilitate translocation of a variety of substrates, MCT8 specifically transports iodothyronines. Mutations in MCT8 are the underlying cause of severe X-linked psychomotor retardation. At the molecular level, such mutations led to deficiencies in substrate translocation due to reduced cell-surface expression, impaired substrate binding, or decreased substrate translocation capabilities. However, the causal relationships between genotypes, molecular features of mutated MCT8, and patient characteristics have not yet been comprehensively deciphered. We investigated the relationship between pathogenic mutants of MCT8 and their capacity to form dimers (presumably oligomeric structures) as a potential regulatory parameter of the transport function of MCT8. Fourteen pathogenic variants of MCT8 were investigated in vitro with respect to their capacity to form oligomers. Particular mutations close to the substrate translocation channel (S194F, A224T, L434W, and R445C) were found to inhibit dimerization of MCT8. This finding is in contrast to those for other transporters or transmembrane proteins, in which substitutions predominantly at the outer-surface inhibit oligomerization. Moreover, specific mutations of MCT8 located in transmembrane helix 2 (del230F, V235M, and ins236V) increased the capacity of MCT8 variants to dimerize. We analyzed the localization of MCT8 dimers in a cellular context, demonstrating differences in MCT8 dimer formation and distribution. In summary, our results add a new link between the functions (substrate transport) and protein organization (dimerization) of MCT8, and might be of relevance for other members of the MFS. Finally, the findings are discussed in relationship to functional data combined with structural-mechanistical insights into MCT8.

Analysis of human TAAR8 and murine Taar8b mediated signaling pathways and expression profile

The thyroid hormone derivative 3-iodothyronamine (3-T₁AM) exerts metabolic effects in vivo that contradict known effects of thyroid hormones. 3-T₁AM acts as a trace amine-associated receptor 1 (TAAR1) agonist and activates G_s signaling in vitro. Interestingly, 3-T₁AM-meditated in vivo effects persist in Taar1 knockout-mice indicating that further targets of 3-T₁AM might exist. Here, we investigated another member of the TAAR family, the only scarcely studied mouse and human trace-amine-associated receptor 8 (Taar8b, TAAR8). By RT-qPCR and locked-nucleic-acid (LNA) in situ hybridization, Taar8b expression in different mouse tissues was analyzed. Functionally, we characterized TAAR8 and Taar8b with regard to cell surface expression and signaling via different G-protein-mediated pathways. Cell surface expression was verified by ELISA, and cAMP accumulation was quantified by AlphaScreen for detection of G_s and/or G_i/o signaling. Activation of G-proteins G_q/11 and G_12/13 was analyzed by reporter gene assays. Expression analyses revealed at most marginal Taar8b expression and no gender differences for almost all analyzed tissues. In heart, LNA-in situ hybridization demonstrated the absence of Taar8b expression. We could not identify 3-T₁AM as a ligand for TAAR8 and Taar8b, but both receptors were characterized by a basal G_i/o signaling activity, a so far unknown signaling pathway for TAARs.

The activity and localization patterns of cathepsins B and X in cells of the mouse gastrointestinal tract differ along its length

Cysteine cathepsins are expressed in most tissues, including the gastrointestinal tract. We demonstrated an involvement of mouse intestinal cathepsin B in extracellular matrix remodeling for regeneration from trauma. The present study aimed at elucidating roles of cysteine cathepsins in the non-traumatized gastrointestinal tract of mice. Thus we investigated expression and localization patterns of cathepsin B and its closest relative, cathepsin X, along the length of the gastrointestinal tract, and determined the effects of their absence. Cathepsin B showed the highest protein levels in the anterior segments of the gastrointestinal tract, whereas the highest activity was observed in the jejunum, as revealed by cathepsin B-specific activity-based probe labeling. Cathepsin X was most abundant in the jejunum and protein levels were elevated in duodenum and colon of Ctsb-/- mice. The segmental pattern of cathepsin expression was reflected by a compartmentalized distribution of junction proteins and basal lamina constituents, changes in tissue architecture and altered activities of the brush border enzyme aminopeptidase N. In conclusion, we observed different compensatory effects and activity levels of cysteine peptidases along the length of the small and large intestines in a segment-specific manner suggesting specific in situ functions of these enzymes in particular parts of the gastrointestinal tract.

[Thyroid hormone action beyond classical concepts. The priority programme "Thyroid Trans Act" (SPP 1629) of the German Research Foundation]

Thyroid hormones are of crucial importance for the function of nearly all organ systems. In case of dysfunction of thyroid hormone production and function many organ systems may be affected. The estimation of normal thyroid function is based on determination of TSH and the thyroid hormones T3 and T4. However, international conventions about the normal TSH range are still lacking which bears consequences for patient`s treatment. Hence not unexpected, many patients complain although their thyroid hormone status is in the normal range by clinical estimation. Here, more precise parameters are needed for a better definition of the healthy thyroid status of an individual. Recently, new key players in the system of thyroid hormone action were detected, like specific transporters for uptake of thyroid hormones and thyroid hormone derivatives. DFG, the German Research Foundation supports the priority program Thyroid Trans Act to find answers to the main question: what defines the healthy thyroid status of an individual. The overall aim of this interdisciplinary research consortium is to specify physiological and pathophysiological functions of thyroid hormone transporters and thyroid hormone derivative as new players in thyroid regulation in order to better evaluate, treat, and prevent thyroid-related disease.