Spatial differences of endogenous lectin expression within the cellular organization of the human heart: a glycohistochemical, immunohistochemical, and glycobiochemical study

Distinct glycosylation in membrane proteins within neonatal versus adult myocardial tissue

Mammalian hearts have regenerative potential restricted to early neonatal stage and lost within seven days after birth. Carbohydrates exclusive to cardiac neonatal tissue may be key regulators of regenerative potential. Although cell surface and extracellular matrix glycosylation are known modulators of tissue and cellular function and development, variation in cardiac glycosylation from neonatal tissue to maturation has not been fully examined. In this study, glycosylation of the adult rat cardiac ventricle showed no variability between the two strains analysed, nor were there any differences between the glycosylation of the right or left ventricle using lectin histochemistry and microarray profiling. However, in the Sprague-Dawley strain, neonatal cardiac glycosylation in the left ventricle differed from adult tissues using mass spectrometric analysis, showing a higher expression of high mannose structures and lower expression of complex N-linked glycans in the three-day-old neonatal tissue. Man₆GlcNAc₂ was identified as the main high mannose N-linked structure that was decreased in adult while higher expression of sialylated N-linked glycans and lower core fucosylation for complex structures were associated with ageing. The occurrence of mucin core type 2 O-linked glycans was reduced in adult and one sulfated core type 2 O-linked structure was identified in neonatal tissue. Interestingly, O-linked glycans from mature tissue contained both N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), while all sialylated N-linked glycans detected contained only Neu5Ac. As glycans are associated with intracellular communication, the specific neonatal structures found may indicate a role for glycosylation in the neonatal associated regenerative capacity of the mammalian heart. New strategies targeting tissue glycosylation could be a key contributor to achieve an effective regeneration of the mammalian heart in pathological scenarios such as myocardial infarction.

Glycosylation of purified buffalo heart galectin-1 plays crucial role in maintaining its structural and functional integrity

A buffalo heart galectin-1 purified by gel filtration chromatography revealed the presence of 3.55% carbohydrate content, thus it is the first mammalian heart galectin found to be glycosylated in nature and emphasizes the need to perform deglycosylation studies. Physicochemical comparative analysis between the properties of the native and deglycosylated proteins was carried out to understand the significance of glycosylation. The deglycosylated protein exhibited lesser thermal and pH stability compared to the native galectin. When exposed to thiol blocking reagents, denaturants, and detergents, remarkable differences were observed in the properties of the native and deglycosylated protein. Compared to the native glycosylated protein, the deglycosylated galectin showed enhanced fluorescence quenching when exposed to various agents. CD and FTIR analysis showed that deglycosylation of the purified galectin and its exposure to different chemicals resulted in significant deviations from regular secondary structure of the protein, thus emphasizing the significance of glycosylation for maintaining the active conformation of the protein. The remarkable differences observed in the properties of the native and deglycosylated galectin add an important dimension to the significance of protein glycosylation and its associated biological and clinical relevance.

Purification, characterization, sequencing and biological chemistry of galectin-1 purified from Capra hircus (goat) heart

A soluble β-galactoside binding 14.5 kDa lectin was purified from the heart of Capra hircus. Its metal independent nature, preferential affinity for β-D-lactose and 90-94% homology with carbohydrate recognition domain of previously reported galectin-1 confirmed its inclusion in galectin-1 subfamily. The secondary structures of the deduced amino acid sequences were generally conserved with previously reported Gal-1. Exposure of the purified protein to varying temperature and pH, oxidant, thiol blocking reagents, denaturants and detergents resulted in significant changes in UV (ultraviolet), fluorescence, CD (circular dichroism) and FTIR (fourier transform infra red) spectra, thus strongly emphasizing the vitality of regular secondary structure of galectins for maintaining their active conformation. Bioinformatics studies corroborated the results obtained in wet lab. Our findings based on physico-chemical properties, oxidative inactivation and structural analysis of the goat heart galectin-1 suggests significant implications in potential biological and clinical applications.

Purification, characterization, structural analysis and protein chemistry of a buffalo heart galectin-1

A soluble β-galactoside-binding lectin was purified by gel filtration chromatography from Bubalus bubalis heart. Its metal-independent nature, molecular weight of 14.5 kDa, preferential affinity for β-D-lactose, and 87-92% identity with carbohydrate recognition domain of previously reported galectin-1 confirmed its inclusion in galectin-1 subfamily. Stokes radii determination using gel filtration under reducing and non-reducing conditions revealed its homo-dimeric nature, further confirming its Gal-1 nomenclature. The purified lectin was found to be the most stable mammalian heart galectin purified till date, suggesting its preferential use in various recognition studies. Treatment of the purified lectin with oxidizing agent, thiol blocking reagents, denaturants, and detergents resulted in significant changes in UV-VIS, fluorescence, CD and FTIR spectra, which strongly emphasized the important aspect of regular secondary structure of galectins for the maintenance of their active conformation. Reduction of the activity of the purified lectin after oxidation by H2O2, with remarkable fluorescence quenching, may suggest potential role for galectin-1 in free radical-induced, oxidative stress-mediated cardiovascular disorders. The predictions of bioinformatics studies were found to be in accordance with the results obtained in wet lab.

Temporal and spatial regulation of expression of two galectins during kidney development of the chicken

Organogenesis and the establishment of the mature phenotype require an interplay between diverse recognition systems. Concerning protein-carbohydrate interactions, galectins are known to be involved in several extra- and intracellular functions. Due to the occurrence of two avian galectins in liver (chicken galectin-16 CG-16) and intestine (chicken galectin-14; CG-14) with different developmental regulation. the questions addressed are to what extent and where these galectins are present during chicken kidney development. Using Western blot analysis, the presence of both activities in tissue extracts was ascertained. A solid-phase assay showed peak levels at day 12 followed by a decline. A histochemical analysis was carried out in combination with routine staining. Epithelial cells of the mesonephric proximal tubules were immunoreactive in the cytoplasm for CG-14 from day 5 of incubation onwards. Additionally, epithelial cells of the metanephric collecting ducts were stained. For CG-16 a rather similar pattern of staining was seen, additional positivity in early glomerular podocytes being notable. At the electron microscopical level, a diffuse staining for CG-14 was seen in the cytoplasm, whereas immunoreactivity for CG-16 was observed mainly in mitochondria. These results demonstrate quantitative differences in the developmental regulation of the two avian galectins with obvious similarities in the cell-type pattern but with a disparate intracellular localisation profile.

Detection of endogenous receptors for carbohydrate ligands in primary and metastatic human renal cell carcinoma

Frozen sections of primary and metastatic human renal cell carcinoma (RCC) were analyzed for the expression of endogenous binding sites for carbohydrates. Fluorescent neoglycoproteins, carrying chemically linked carbohydrate residues on bovine serum albumin as a carrier protein, were applied to 44 primary tumor specimens. In the majority of specimens, accessible binding sites with specificity for maltose and N-acetylgalactosamine were detected. In specimens of normal kidney no specific binding of carbohydrate ligands was observed under these experimental conditions. Specimens of both the primary tumor and a metastasis were available in 10 cases. When the expression of specific binding sites of primary tumors and metastases was compared, the respective patterns were similar with no clear gain or loss of certain lectins in the metastases. We conclude that binding sites with specificity for maltose and N-acetylgalactosamine are present on human RCC and their corresponding metastases.

A critical evaluation of neoglycoprotein binding sites in vivo and in sections of mouse tissues

Endogenous lectins are reported to play a vital role in cell to cell communication. Their distribution in tissues has been widely studied by the use of labelled neoglycoproteins. In the present study, labelled neoglycoproteins were used on fixed and unfixed tissue sections and the results were compared with those observed after i.v. application of neoglycoproteins in mice. The study indicates that neoglycoprotein binding to tissue sections is not inhibited by application of the simple monosaccharides that were used to synthesize them. Furthermore the binding of neoglycoproteins following i.v. application into mice is rather limited. It is concluded that neoglycoproteins, which are synthesized using simple monosaccharides, do not provide a sensible tool to detect endogenous lectins in animal tissue sections. This is in sharp contrast to the results of most other studies reported in the literature.

Localization of endogenous beta-galactoside-specific lectins by neoglycoproteins, lectin-binding tissue glycoproteins and antibodies and of accessible lectin-specific ligands by mammalian lectin in human breast carcinomas

Protein-carbohydrate interactions constitute a system of molecular interaction with relevance to pathologic conditions. Carrier-immobilized carbohydrate structures enable the histochemical investigation of the protein part of this recognitive system. However, thorough systematic studies are inevitably required for standardized application of this relatively novel class of markers. Consequently, serial sections of 21 cases of malignant breast lesion were comparatively analyzed with three different types of probe, specific for beta-galactoside-binding lectins. In addition to the chemically lactosylated neoglycoprotein, human lectin-binding glycoproteins, purified by affinity chromatography on resins with an immobilized beta-galactoside-specific lectin, and a lectin-specific antibody were employed to answer the question whether differences occur in their capacity for lectin localization. The patterns of staining were qualitatively similar, the lectin-binding glycoproteins yielding the most intense reaction. Having assured the reliable applicability of the neoglycoprotein, structural alterations of the subterminal carbohydrate residue on the labelled carrier addressed the issue, whether selectivity of binding can be inferred histochemically, allowing rational synthetic tailoring. An N-acetylglucosamine residue in beta-1,3-linkage proved to be a less favorable extension than this type of sugar in beta-1,4-linkage or an N-acetylgalactosamine moiety in beta-1,3-linkage. Binding was clearly reduced in cells of normal breast tissue with this probe. In order to gain evidence on the expression of potential carbohydrate ligands for the glyco- and immunohistochemically localized binding activity, a labelled mammalian beta-galactoside-specific lectin was similarly used as histochemical tool. It effectively bound to accessible sites in the sections. The binding pattern was different to that of plant lectins with specificity to beta-galactosides. This result underscores that caution is necessary in the functional interpretation of results of studies with plant, not mammalian lectins.(ABSTRACT TRUNCATED AT 250 WORDS)