Mouse lipocalin as an enhancer of spermatozoa motility

Overview of the expression patterns and roles of Lipocalin 2 in the reproductive system

The 25 kDa-sized protein Lipocalin 2 (LCN2) was originally isolated from human neutrophil granulocytes more than 30 years ago. LCN2 is an emerging player in innate immune defense, as it reduces bacterial growth due to its ability to sequester iron-containing bacterial siderophores. On the other hand, LCN2 also serves as a transporter for various hydrophobic substances due to its β-barrel shaped structure. Over the years, LCN2 has been detected in many other cell types including epithelial cells, astrocytes, and hepatocytes. Studies have clearly shown that aberrant expression of LCN2 is associated with a variety of disorders and malignancies, including several diseases of the reproductive system. Furthermore, LCN2 was proposed as a non-invasive prognostic and/or diagnostic biomarker in this context. Although several studies have shed light on the role of LCN2 in various disorders of the female and male reproductive systems, including tumorigenesis, a comprehensive understanding of the physiological function of LCN2 in the reproductive tract is still lacking. However, there is evidence that LCN2 is directly related to fertility, as global depletion of Lcn2 in mice has a negative effect on their pregnancy rate. Since LCN2 expression can be regulated by steroid hormones, it is not surprising that its expression fluctuates greatly during remodeling processes in the female reproductive tract, especially in the uterus. Well-founded details about the expression and regulation of LCN2 in a healthy reproductive state and also about possible changes during reproductive aging could contribute to a better understanding of LCN2 as a target in various diseases. Therefore, the present review summarizes current knowledge about LCN2 in the reproductive system, including studies in rodents and humans, and discusses changes in LCN2 expression during pathological events. The limited data suggest that LCN2 is expressed and regulated differently in healthy male and female reproductive organs.

Serum Lipocalin-2 Levels as a Biomarker in Pre- and Post-Pubertal Klinefelter Syndrome Patients: A Pilot Study

Klinefelter syndrome (KS) is a male genetic disease caused by the presence of an extra X chromosome, causing endocrine disorders mainly responsible for a high rate of infertility and metabolic disorders in adulthood. Scientific research is interested in identifying new biomarkers that can be predictive or prognostic of alterations strictly connected to KS. Lipocalin-2 (LCN-2, also known as NGAL) is a small protein initially identified within neutrophils as a protein related to innate immunity. Serum LCN-2 estimation seems to be a useful tool in predicting the metabolic complications caused by several pathological conditions. However, little is known about its potential role in infertility conditions. The present pilot study aims to investigate the presence of LCN-2 in the serum of a group of pre-pubertal and post-pubertal children affected by KS, compared to healthy controls. We demonstrated for the first time the presence of elevated levels of LCN-2 in the serum of KS patients, compared to controls. This increase was accompanied, in pre-pubertal KS patients, by the loss of correlation with LH and HDL, which instead was present in the healthy individuals. Moreover, in all KS individuals, a positive correlation between LCN-2 and inhibin B serum concentration was found. Despite the limited size of the sample analyzed, our preliminary data encourage further studies to confirm the findings and to extend the study to KS adult patients, to verify the predictive/prognostic value of LCN-2 as new biomarker for metabolic diseases and infertility associated with the pathology.

Identification, characterization and expression analysis of rLcn13, an epididymal lipocalin in rats

As the essential tissue for sperm maturation and storage, the epididymis secretes a number of tissue-specific proteins to exert its functions. Among these proteins, epididymal lipocalins have been intensively studied because of their epididymis-specific expression pattern and clustered genomic organization. In this study, rLcn13, a member of the rat epididymal lipocalin family, is identified and elaborately characterized. The cDNA sequence of rLcn13 consists of 719 nucleotides and encodes a 176 amino-acid protein with a predicted N-terminal signal peptide of 19 amino acids. rLcn13 shares a similar genomic structure and predicted 3D protein structure with other lipocalin family members. A recombinant rLCN13 mature peptide of 157 amino acids is expressed and purified, which is used to raise a polyclonal antibody against rLCN13 with high specificity and sensitivity. Northern blot, western blot, and immunohistochemistry assays reveal that rLcn13 is an epididymis-specific gene which is expressed predominantly in the initial segment and proximal caput epididymis and influenced by androgen. The rLCN13 protein is modified by N-glycosylation and secreted into the epididymal lumen, and then binds to the acrosome region of the sperm. Our data demonstrate that rLcn13 exhibits a specific temporospatial expression pattern and androgen dependence, indicating its potential roles in sperm maturation.

Lipocalin-2: a novel link between the injured kidney and the bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) excess is associated with left ventricular hypertrophy (LVH) and early mortality in patients with chronic kidney disease (CKD) and in animal models. Elevated Lipocalin-2 (LCN2), produced by the injured kidneys, contributes to CKD progression and might aggravate cardiovascular outcomes. The current review aims to highlight the role of LCN2 in CKD, particularly its interactions with FGF23.

RECENT FINDINGS

Inflammation, disordered iron homeostasis and altered metabolic activity are common complications of CKD, and are associated with elevated levels of kidney-produced LCN2 and bone-secreted FGF23. A recent study shows that elevated LCN2 increases FGF23 production, and contributes to cardiac injury in patients and animals with CKD, whereas LCN2 reduction in mice with CKD reduces FGF23, improves cardiovascular outcomes and prolongs lifespan.

SUMMARY

In this manuscript, we discuss the potential pathophysiological functions of LCN2 as a major kidney-bone crosstalk molecule, linking the progressive decline in kidney function to excessive bone FGF23 production. We also review associations of LCN2 with kidney, cardiovascular and bone and mineral alterations. We conclude that the presented data support the design of novel therapeutic approaches to improve outcomes in CKD.

Biological Roles of Lipocalins in Chemical Communication, Reproduction, and Regulation of Microbiota

Major evolutionary transitions were always accompanied by genetic remodelling of phenotypic traits. For example, the vertebrate transition from water to land was accompanied by rapid evolution of olfactory receptors and by the expansion of genes encoding lipocalins, which - due to their transporting functions - represent an important interface between the external and internal organic world of an individual and also within an individual. Similarly, some lipocalin genes were lost along other genes when this transition went in the opposite direction leading, for example, to cetaceans. In terrestrial vertebrates, lipocalins are involved in the transport of lipophilic substances, chemical signalling, odour reception, antimicrobial defence and background odour clearance during ventilation. Many ancestral lipocalins have clear physiological functions across the vertebrate taxa while many other have - due to pleiotropic effects of their genes - multiple or complementary functions within the body homeostasis and development. The aim of this review is to deconstruct the physiological functions of lipocalins in light of current OMICs techniques. We concentrated on major findings in the house mouse in comparison to other model taxa (e.g., voles, humans, and birds) in which all or most coding genes within their genomes were repeatedly sequenced and their annotations are sufficiently informative.

Zika virus disrupts the barrier structure and Absorption/Secretion functions of the epididymis in mice

Several studies have demonstrated that Zika virus (ZIKV) damages testis and leads to infertility in mice; however, the infection in the epididymis, another important organ of male reproductive health, has gained less attention. Previously, we detected lesions in the epididymis in interferon type I and II receptor knockout male mice during ZIKV infection. Herein, the pathogenesis of ZIKV in the epididymis was further assessed in the infected mice after footpad inoculation. ZIKV efficiently replicated in the epididymis, and principal cells were susceptible to ZIKV. ZIKV infection disrupted the histomorphology of the epididymis, and the effects were characterized by a decrease in the thickness of the epithelial layer and an increase in the luminal diameter, especially at the proximal end. Significant inflammatory cell infiltration was observed in the epididymis accompanied by an increase in the levels of interleukin (IL)-6 and IL-28. The expression of tight junction proteins was downregulated and associated with disordered arrangement of the junctions. Importantly, the expression levels of aquaporin 1 and lipocalin 8, indicators of the absorption and secretion functions of the epididymis, were markedly reduced, and the proteins were redistributed. These events synergistically altered the microenvironment for sperm maturation, disturbed sperm transport downstream, and may impact male reproductive health. Overall, these results provide new insights into the pathogenesis of the male reproductive damage caused by ZIKV infection and the possible contribution of epididymal injury into this process. Therefore, male fertility of the population in areas of ZIKV epidemic requires additional attention.

Unlike other mosquito-transmitted flaviviruses, ZIKV can persistently replicate in the male reproductive system and is sexually transmitted. ZIKV infection was reported to damage testis. However, ZIKV-induced epididymal injury was not investigated in detail. Clinically, epididymitis is closely associated with male infertility. In this study, a mouse model was used to demonstrate that ZIKV causes histomorphological and functional changes in the epididymis, which may alter the microenvironment of sperm maturation and movement and finally lead to male infertility. Therefore, long-term investigation of male reproductive health may be needed in the areas of ZIKV epidemic.

Ovarian fluid proteome variation associates with sperm swimming speed in an externally fertilizing fish

Sperm velocity is a key trait that predicts the outcome of sperm competition. By promoting or impeding sperm velocity, females can control fertilization via postcopulatory cryptic female choice. In Chinook salmon, ovarian fluid (OF), which surrounds the ova, mediates sperm velocity according to male and female identity, biasing the outcome of sperm competition towards males with faster sperm. Past investigations have revealed proteome variation in OF, but the specific components of OF that differentially mediate sperm velocity have yet to be characterized. Here we use quantitative proteomics to investigate whether OF protein composition explains variation in sperm velocity and fertilization success. We found that OF proteomes from six females robustly clustered into two groups and that these groups are distinguished by the abundance of a restricted set of proteins significantly associated with sperm velocity. Exposure of sperm to OF from females in group I had faster sperm compared to sperm exposed to the OF of group II females. Overall, OF proteins that distinguished between these groups were enriched for vitellogenin and calcium ion interactions. Our findings suggest that these proteins may form the functional basis for cryptic female choice via the biochemical and physiological mediation of sperm velocity.

The maturation of murine spermatozoa membranes within the epididymis, a computational biology perspective

To become fertile, mammalian spermatozoa require completing a complex biochemical maturation that begins in the testis and ends within the female oviduct. Here, we paid attention to the events occurring at the membrane level during the epididymal transit. Indeed, in the epididymis, the molecular composition and the physical-chemical proprieties of sperm membranes markedly change, with functional cross talking among the spermatozoa, the epithelium, and the luminal content (particularly the epididymosomes). To study this process, we undertook a biological networks study, representing the involved molecules as nodes and their interactions as links. The analysis of network topology revealed that it has a scale free and small world architecture and it is robust against random failure. That assures a fast and efficient transmission of information and it leads to identifying the molecules exerting a higher level of control on the system, among which cholesterol plays a pivotal role. The reactome enrichment analysis allowed the reconstruction of the biochemical pathways involved in sperm epididymal maturation and STRING analysis permitted the identification of molecular events possibly involved in that process. In conclusion, this approach allows inferring interesting information, thus contributing to the knowledge on this process and suggesting staring points for further research.

Progesterone induces the expression of lipocalin-2 through Akt-c-Myc pathway during mouse decidualization

Lipocalin-2 (Lcn2) is a small glycoprotein involved in a number of biological processes such as inflammation and antibacterial response. In our study, Lcn2 is expressed in the subluminal stromal cells at implantation site on day 5 of pregnancy. The expression of Lcn2 in stromal cells is under the control of progesterone through Akt-c-Myc signaling pathway. Data from Lcn2 knockdown and recombinant protein treatments indicate that Lcn2 promotes mPGES-1 expression in stromal cells. The expression of Lcn2 and mPGES-1 is strongly stimulated by lipopolysaccharide (LPS), indicating that Lcn2 mediates LPS-induced inflammation. These findings shed light on the role of Lcn2 during decidualization.

Effect of incorporation of additives in tris-based egg yolk extender on buffalo (Bubalus bubalis) sperm tyrosine phosphorylation during cryopreservation

Phosphorylation of tyrosine residues on sperm protein is a known indicator of capacitation and a major intracellular signalling event. There is evidence that sperm cryopreservation promotes tyrosine phosphorylation and is associated with reduced fertility of spermatozoa. Under this study, cryoprotective role of different additives namely taurine, trehalose, catalase and 4-bromophenacyl bromide on buffalo sperm quality was evaluated. Buffalo semen was cryopreserved in tris-based egg yolk extender supplemented with additives like taurine (50 mm) or trehalose (100 mm) or 4-bromophenacyl bromide (200 μm) or catalase (100 U/ml) and used for assessment of levels of tyrosine phosphorylation in frozen-thawed spermatozoa. The results obtained were compared with the level of protein tyrosine phosphorylation of semen cryopreserved in tris-based egg yolk extender without additives. Proteins were extracted from a total number of nine ejaculates from three individual buffalo bulls chosen at random and analysed for tyrosine phospho-proteins using SDS-PAGE followed by immunoblotting. Monoclonal anti-phosphotyrosine antibody (Clone pT-154) was used as primary antibody followed by treatment with HRP-conjugated secondary antibody. Signals were detected on X-ray film using chemiluminescence. Nine proteins (p20, p30, p32, p38, p49, p56, p59, p72 and p86) were found to be tyrosine phosphorylated in cryopreserved spermatozoa. Supplementation of additives significantly (p<0.05) reduced the level of protein tyrosine phosphorylation in spermatozoa. Moreover, this study showed improved (p<0.05) post-thaw motility, viability and membrane integrity of spermatozoa on addition of these additives. The results obtained clearly indicate reduced level of capacitation like changes on supplementation of additives in terms of protein tyrosine phosphorylation.

Isolation of lipocalin-type protein from rainbow trout seminal plasma and its localisation in the reproductive system

The lipocalin protein family is a large and diverse group of small extracellular proteins characterised by their ability to bind hydrophobic molecules. In the present study, we describe the isolation procedure for rainbow trout seminal plasma protein, characterised by a moderate migration rate during polyacrylamide gel electrophoresis, providing information regarding its basic features and immunohistochemical localisation. This protein was identified as a lipocalin-type protein (LTP). The molecular mass of LTP was found to be 18 848 Da and it was found to lack any carbohydrate components. Only a few Salmoniformes contain LTP in their seminal plasma. The abundance of LTP in the Sertoli and Leydig cells of the testes of the rainbow trout, as well as in secretory cells of the efferent duct, suggests that this protein is specific for rainbow trout milt, where it acts as a lipophilic carrier protein. Moreover, the specific localisation of LTP in the flagella of the spermatozoa suggests a role for LTP in sperm motility. Further experiments are necessary to identify the endogenous ligands for LTP in rainbow trout seminal plasma and to characterise the binding properties of this protein.

Atlas of dihydrotestosterone actions on the transcriptome of prostate in vivo

BACKGROUND

Using serial analysis of gene expression (SAGE), we studied the transcriptomic changes in vivo by dihydrotestosterone (DHT) treatment in mice to better understand androgen effects in the prostate.

METHODS

Approximately 872,000 SAGE tags were isolated from intact and castrated (GDX) mice with and without DHT injection.

RESULTS

GDX significantly altered 431 transcripts, including 110 transcripts restored by DHT, and 146 potentially new transcripts. Totally, 187 transcripts were significantly affected by DHT treatment, of which 124 were induced and 63 were repressed. Interestingly and consistent with the prostate's secretory role, DHT up-regulated the expression of many genes involved in various steps of protein metabolism such as synthesis, folding, and secretion. GDX modulated the expression of genes which induce cell apoptosis and inhibit cell proliferation through polyamine biosynthesis, retinoid X receptor actions as well as several signaling pathways and some related factors. These results clarify DHT effects on prostate transcriptome in the areas of protein metabolism, cell proliferation and apoptosis. In addition, we detected gene expression changes in metabolic pathways, cytoskeleton, immunity and endoplasmic reticulum stress. Furthermore, knockdown of S-adenosylmethionine decarboxylase 1 in LNCaP cells confirmed the importance of androgen-regulated genes (ARGs) in prostate cancer cell growth.

CONCLUSION

Our data support the idea that ARGs are essential for the normal development of the prostate and can also be responsible for the pathogenesis of the prostate cancer.

Glycomics and proteomics analyses of mouse uterine luminal fluid revealed a predominance of Lewis Y and X epitopes on specific protein carriers

Sperm motility and maturation are known to be affected by a host of factors encountered en route in both male and female genital tracts prior to fertilization. Using a concerted proteomics and glycomics approach with advanced mass spectrometry-based glycan sequencing capability, we show in this work that 24p3, an abundant mouse uterine luminal fluid (ULF) glycoprotein also called lipocalin 2 (Lcn2), is highly fucosylated in the context of carrying multiple Lewis X and Y epitopes on complex type N-glycans at its single glycosylation site. The predominance of Lewis X/Y along with Neu5Acalpha2-6 sialylation was found to be a salient feature of the ULF glycome, and several other protein carriers were additionally identified including the highly abundant lactotransferrin, which is N-glycosylated at two sites, both with a similar range of highly fucosylated N-glycans. A comparative glycomics analysis of the male genital tract fluids revealed that there is a gradient of glycomic complexity from the cauda to caput regions of the epididymis, varying from high mannose to sialylated complex type N-glycans but mostly devoid of fucosylation. The seminal vesicle fluid glycome, on the other hand, carries equally abundant multimeric Lewis X structures but is distinctively lacking in additional fucosylation of the terminal galactose to give the Lewis Y epitope typifying the glycome of female ULF. One-dimensional shotgun proteomics analysis identified over 40 proteins in the latter, many of which are reported for the first time, and a majority are notably involved in immune defense and antigen processing. Further sperm binding and motility assays suggest that the Lewis X/Y epitopes do contribute to the sperm motility-enhancing activity of 24p3, whereas lactotransferrin is largely inactive in this context despite being similarly glycosylated. These findings underline the importance of glycoproteomics in delineating both the specific glycan structures and their carriers in assigning glycobiological functions.

Mouse uterine 24p3 protein as a suppressor of sperm acrosome reaction

Under in vitro conditions, incubation with 0.3% bovine serum albumin (BSA) and 1.8 mM CaCl(2) induces mouse sperm capacitation and increases the consequential acrosome-reaction. The effect of mouse uterine 24p3 protein on such stimulated sperm has been investigated to understand the biological function of the 24p3 protein. Variations in the intracellular pH (pHi), calcium concentration, cAMP levels and tyrosine phosphorylation in cytosol were determined and on in vitro mouse fertilization was evaluated. The presence of 24p3 protein reduced the response of sperm to BSA and calcium by suppressing the elevation of intracellular pH, calcium uptake, cAMP accumulation and protein tyrosine phosphorylation of BSA/calcium-stimulated sperm and showed inhibitory effect on mouse in vitro fertilization. The results indicated the inhibition of the BSA-stimulated sperm acrosome reaction by 24p3 protein then suppressed sperm fertilization. We suggested that the 24p3 protein acts as an in vitro inhibitor of the acrosome reaction in BSA stimulated sperm and this might be an anti-fertilization factor in vitro.

Induction of iron homeostasis genes during estrogen-induced uterine growth and differentiation

We have previously used genome-wide transcript profiling to investigate the relationships between changes in gene expression and physiological alterations during the response of the immature mouse uterus to estrogens. Here we describe the identification of a functionally inter-related group of estrogen-responsive genes associated with iron homeostasis, including the iron-binding protein lactotransferrin, the ferroxidase ceruloplasmin, the iron delivery protein lipocalin 2 and the iron-exporter ferroportin. Quantitative real-time PCR revealed that the expression of these genes increases with time during the uterotrophic response, reaching maximal levels in the post-proliferative phase (between 48 and 72 h). In contrast, the heme biosynthesis genes aminolevulinic acid synthase 1 and 2 were maximally induced by estrogen at 2 and 4 h, respectively, prior to increased cell proliferation. Together, these data reveal that estrogen induces the temporally coordinated expression of iron homeostasis genes in the mouse uterus, and suggest an important role for iron metabolism during sex steroid hormone-induced uterine cell growth and differentiation.

Lipocalin 2-deficient mice exhibit increased sensitivity to Escherichia coli infection but not to ischemia-reperfusion injury

Diverse functions have been reported for lipocalin 2. To investigate these functions in vivo, we generated gene-targeted lipocalin 2-deficient mice (Lcn2-/- mice). In vitro studies have suggested that lipocalin 2 is important for cellular apoptosis induced by IL-3 withdrawal, and for the induction of kidney differentiation during embryogenesis. Analysis of Lcn2-/- mice showed normal cell death upon IL-3 withdrawal and normal kidney development. However, we found that Lcn2-/- mice exhibited an increased susceptibility to bacterial infections, in keeping with the proposed function of lipocalin 2 in iron sequestration. Neutrophils isolated from Lcn2-/- mice showed significantly less bacteriostatic activity compared with WT controls. The bacteriostatic property of the WT neutrophils was abolished by the addition of exogenous iron, indicating that the main function of lipocalin 2 in the antibacterial innate immune response is to limit this essential element. Another important function ascribed to lipocalin 2 has been its protective role against kidney ischemia-reperfusion injury. We analyzed Lcn2-/- mice using a mouse model for severe renal failure and could not detect any significant differences compared with their WT littermates.

Spermatogonial cell-mediated activation of an IkappaBzeta-independent nuclear factor-kappaB pathway in Sertoli cells induces transcription of the lipocalin-2 gene

In spermatogenesis, Sertoli cells serve as supporting cells for the proliferation and differentiation of germ cells. However, it appears that Sertoli cell function is regulated by adjacent spermatogonial cells in the testis because expression of lipocalin-2 mRNA, which encodes an iron-siderophore-binding protein, is barely detectable in Sertoli cells of germ cell-deficient W/Wv mice, and more abundantly expressed in jsd/jsd mice. By employing a coculture system comprising immortalized Sertoli cells (designated as Sertoli-B) and c-Kit(+) spermatogonial cells from 7-d-old mouse testis, we found that lipocalin-2 gene transcription in Sertoli cells is induced by a factor secreted from spermatogonial cells. Transfection of Sertoli-B cells with a series of reporter constructs encompassing an upstream region of the mouse lipocalin-2 gene revealed that a nuclear factor (NF)-kappaB binding consensus sequence in the proximal region of lipocalin-2 gene is responsible for transcriptional activation. A major NF-kappaB component, p65, bound to this region and translocated from the cytoplasm to the nucleus upon stimulation with spermatogonial cell-conditioned medium. Moreover, short interference RNA directed to p65 or a dominant-negative form of IkappaBalpha suppressed the spermatogonial cell factor-mediated transcription of lipocalin-2. However, NF-kappaB-activating inflammatory molecules, such as IL-1beta and lipopolysaccharide, did not induce lipocalin-2 mRNA in Sertoli-B cells and the expression of lipocalin-2 was unaffected in the testis of IkappaBzeta-deficient mice. These results demonstrate that spermatogonial cells regulate lipocalin-2 gene expression in Sertoli cells in a manner distinct from that employed by immune cells.

Delivery of ferric ion to mouse spermatozoa is mediated by lipocalin internalization

The aim of this study was to illustrate the further process of 24p3 protein after association with epididymal spermatozoa. We have previously identified a caput-initiated 24p3 protein, which interacts with the spermatozoa surface in vitro. In the present study, we investigate another role of the 24p3 protein with spermatozoa. Mouse epididymal spermatozoa exhibit the ability to bind spontaneously with exogenous 24p3 protein, a part of which is further internalized into the spermatozoa in epididymal caput. We have now focused on this issue using freshly prepared spermatozoa from caudal region of epididymis. First, the cytosolic fractionation of spermatozoa has revealed that biotinylated 24p3 protein signal could be detected by supplying biotinylated protein under 37 degrees C incubation after 30 min at this experiment. Further, flow cytometric analysis of FITC-protein containing spermatozoa has revealed two distinct types of fluorescent spermatozoa, and microscopical experimentation with fluorescent FITC-24p3 protein has shown that the 24p3 protein did accumulate in the cytosolic portion of spermatozoa. All of these events, which showed protein uptake into the cell, demonstrated time- and temperature-dependence of endocytotic characteristics, these constituting the critical points in the process of endocytosis for spermatozoa as for other cells. Using a fluorometric method, the binding affinities of ferrous ion and ferric ion to 24p3 protein were shown to be (1.5+/-0.2)x10(6) and (3.0+/-0.4)x10(7)M(-1), respectively. We have also determined the internalization of this protein in the transition of iron into spermatozoa. We report here that spermatozoa, from the caudal epididymis, demonstrate the ability to bind with 24p3 protein and further internalize it and deliver the ferric ion to the spermatozoa via protein internalization. We suggest that the 24p3 protein plays a physiological role in spermatozoa in the context of protein-ligand complex internalization.