Analyses of temporal regulatory elements of the prosaposin gene in transgenic mice

Two short antimicrobial peptides derived from prosaposin-like proteins in the starry flounder (Platichthys stellatus)

Prosaposin (PSAP) is a precursor of saposin (SAP), which is present in lysosomal and secreted proteins. PSAP is a member of the SAP-like protein families, which comprise multifunctional proteins. In particular, their antimicrobial activity has been reported. We identified PSAP-like (PsPSAPL) sequences from starry flounder and analysed their expression and antimicrobial activity based on cDNA and amino acid sequences. PsPSAPL showed conservation of three saposin B type domains at high levels, and PsPSAPL mRNA was relatively abundantly distributed in the brain and gills of healthy starry founders. PsPSAPL mRNA showed significant expression changes in response to viral haemorrhagic septicaemia virus and Streptococcus parauberis. Synthetic peptides (PsPSAPL-1 and -2), prepared based on amino acid sequences, were used to confirm as well as analyse the antimicrobial activity against bacteria and parasites. Consequently, PsPSAPL-1 and -2 were found to significantly inhibit the growth of various bacteria and kill the Miamiensis avidus. In addition, bacterial biofilm formation was significantly inhibited. Safety was also confirmed by analysing cell haemolysis. These results indicate the immunological function of PsPSAP and the potential antimicrobial activity of the AMPs PsPSAPL-1 and -2.

Role of saposin C and D in auditory and vestibular function

OBJECTIVES/HYPOTHESIS

Saposins are small proteins derived from a precursor protein, prosaposin. Each of the four saposins (A-D) is necessary for the activity of lysosomal glycosphingolipid hydrolases. Individual saposin mutations lead to lysosomal storage diseases, some of which are associated with hearing loss. Here we evaluate the effects of the loss of saposins C and D on auditory and vestibular function in transgenic mice.

METHODS

Transgenic mice with either loss of saposin C function or a combined loss of saposin C + D function were studied. Light microscopy and immunofluorescence were used to evaluate histologic and morphologic changes in the auditory and vestibular organs. Acoustic brainstem response thresholds and distortion product otoacoustic emissions were used to study the auditory phenotype.

RESULTS

A null mutation of saposin C did not result in any identifiable histologic changes or loss of hearing through postnatal day 55. Combined losses of saposins C and D similarly did not result in any changes in organ of Corti histology or loss of hearing. However, inclusions within the vestibular end organs was noted, consistent with afferent and efferent neuronal sprouting, although to a much milder degree than seen in the previously studied prosaposin knockout mouse.

CONCLUSIONS

Loss of saposin C and D function, although causing mild phenotypic changes in the vestibular end organs, otherwise results in minimal functional impairment and no changes in the auditory system. It is more likely that the auditory and vestibular effects of the loss of prosaposin are mediated through the actions of saposin A and/or B.

LEVEL OF EVIDENCE

NA.

Transcript variants, expression, and polymorphisms of the pig prosaposin gene

Prosaposin (PASP) is a sphingolipid hydrolysis protein that plays roles in both the nervous and reproduction systems. In this study, we cloned the pig PASP gene and studied its genomic organization, polymorphism, and expression pattern. Two PASP transcripts, TV1 (HQ245644) and TV2 (HQ245646), were identified in pig. TV1 was the complete transcript that encoded 527 amino acids, whereas TV2 was 9 bp shorter due to an exon 8 deletion. The pig PASP gene spanned over 34 kb in length on chromosome 14 (SSC14), and consisted of 15 exons and 14 introns. The pig PASP gene (TV1 and TV2) expressed predominantly in the cerebellum, lymphnode, pituitary, abdominal fat, hypothalamus, and cerebrum in both females and males. PASP TV1 expressed mainly in teh cerebrum, cerebellum, hypothalamus, pituitary, heart, subcutaneous fat, and foreleg muscle, while TV2 was expressed in the liver, spleen, lung, kidney, and lymphnode. In foreleg muscle, the predominant transcript was TV2 in males and TV1 in females. Some potential transcriptional elements were predicted in 5' flanking region (~3000 bp) of the PASP gene, and they were TATA boxes, RORE, Sp1, SRY, oct-1, Cdx A, and cap. Additionally, we identified 68 single-nucleotide polymorphisms and 9 indels in the pig PASP gene, and three single-nucleotide polymorphisms (C77932320T or L15F; C77928094T or P191L; A77917401G or K522R) were nonsynonymous substitutions. These results provide useful information for future functional investigations of the pig PASP gene.

Temporal gene expression profiling reveals CEBPD as a candidate regulator of brain disease in prosaposin deficient mice

Background

Prosaposin encodes, in tandem, four small acidic activator proteins (saposins) with specificities for glycosphingolipid (GSL) hydrolases in lysosomes. Extensive GSL storage occurs in various central nervous system regions in mammalian prosaposin deficiencies.

Results

Our hypomorphic prosaposin deficient mouse, PS-NA, exhibited 45% WT levels of brain saposins and showed neuropathology that included neuronal GSL storage and Purkinje cell loss. Impairment of neuronal function was observed as early as 6 wks as demonstrated by the narrow bridges tests. Temporal transcriptome microarray analyses of brain tissues were conducted with mRNA from three prosaposin deficient mouse models: PS-NA, prosaposin null (PS-/-) and a V394L/V394L glucocerebrosidase mutation combined with PS-NA (4L/PS-NA). Gene expression alterations in cerebrum and cerebellum were detectable at birth preceding the neuronal deficits. Differentially expressed genes encompassed a broad spectrum of cellular functions. The number of down-regulated genes was constant, but up-regulated gene numbers increased with age. CCAAT/enhancer-binding protein delta (CEBPD) was the only up-regulated transcription factor in these two brain regions of all three models. Network analyses revealed that CEBPD has functional relationships with genes in transcription, pro-inflammation, cell death, binding, myelin and transport.

Conclusion

These results show that: 1) Regionally specific gene expression abnormalities precede the brain histological and neuronal function changes, 2) Temporal gene expression profiles provide insights into the molecular mechanism during the GSL storage disease course, and 3) CEBPD is a candidate regulator of brain disease in prosaposin deficiency to participate in modulating disease acceleration or progression.

Combined saposin C and D deficiencies in mice lead to a neuronopathic phenotype, glucosylceramide and α-hydroxy ceramide accumulation, and altered prosaposin trafficking

Saposins (A, B, C and D) are approximately 80 amino acid stimulators of glycosphingolipid (GSL) hydrolases that derive from a single precursor, prosaposin. In both humans and mice, prosaposin/saposin deficiencies lead to severe neurological deficits. The CD-/- mice with saposin C and D combined deficiencies were produced by introducing genomic point mutations into a critical cysteine in each of these saposins. These mice develop a severe neurological phenotype with ataxia, kyphotic posturing and hind limb paralysis. Relative to prosaposin null mice ( approximately 30 days), CD-/- mice had an extended life span ( approximately 56 days). Loss of Purkinje cells was evident after 6 weeks, and storage bodies were present in neurons of the spinal cord, brain and dorsal root ganglion. Electron microscopy showed well-myelinated fibers and axonal inclusions in the brain and sciatic nerve. Marked accumulations of glucosylceramides and alpha-hydroxy ceramides were present in brain and kidney. Minor storage of lactosylceramide (LacCer) was observed when compared with tissues from the prosaposin null mice, suggesting a compensation in LacCer degradation by saposin B for the saposin C deficiency. Skin fibroblasts and tissues from CD-/- mice showed an increase of intracellular prosaposin, impaired prosaposin secretion, deficiencies of saposins C and D and decreases in saposins A and B. In addition, the deficiency of saposin C in CD-/- mice resulted in cellular decreases of acid beta-glucosidase activity and protein. This CD null mouse model provides a tool to explore the in vivo functional interactions of saposins in GSL metabolism and lysosomal storage diseases, and prosaposin's physiological effects.

Retinoid-related Orphan Receptors (RORs): Roles in Cellular Differentiation and Development

Retinoid-related orphan receptors RORalpha, -beta, and -gamma are transcription factors belonging to the steroid hormone receptor superfamily. During embryonic development RORs are expressed in a spatial and temporal manner and are critical in the regulation of cellular differentiation and the development of several tissues. RORalpha plays a key role in the development of the cerebellum particularly in the regulation of the maturation and survival of Purkinje cells. In RORalpha-deficient mice, the reduced production of sonic hedgehog by these cells appears to be the major cause of the decreased proliferation of granule cell precursors and the observed cerebellar atrophy. RORalpha has been implicated in the regulation of a number of other physiological processes, including bone formation. RORbeta expression is largely restricted to several regions of the brain, the retina, and pineal gland. Mice deficient in RORbeta develop retinal degeneration that results in blindness. RORgamma is essential for lymph node organogenesis. In the intestine RORgamma is required for the formation of several other lymphoid tissues: Peyer's patches, cryptopatches, and isolated lymphoid follicles. RORgamma plays a key role in the generation of lymphoid tissue inducer (LTi) cells that are essential for the development of these lymphoid tissues. In addition, RORgamma is a critical regulator of thymopoiesis. It controls the differentiation of immature single-positive thymocytes into double-positive thymocytes and promotes the survival of double-positive thymocytes by inducing the expression of the anti-apoptotic gene Bcl-X(L). Interestingly, all three ROR receptors appear to play a role in the control of circadian rhythms. RORalpha positively regulates the expression of Bmal1, a transcription factor that is critical in the control of the circadian clock. This review intends to provide an overview of the current status of the functions RORs have in these biological processes.

Saposin C is required for normal resistance of acid beta-glucosidase to proteolytic degradation

Saposins (A, B, C, and D) are small sphingolipid activator proteins that are derived by proteolytic processing of a common precursor, prosaposin. In the lysosomal sphingolipid degradation pathway, acid beta-glucosidase (GCase) requires saposin C for optimal in vitro and in vivo hydrolysis of glucocerebroside. The deficiency of prosaposin/saposins (PS-/-) in humans and mice leads to a decrease of GCase activity in selected tissues. Concordant decreases (>50%) of GCase protein and in vitro activity were detected in extracts of cultured fibroblasts and hepatocytes from PS-/- mice and human prosaposin-deficient fibroblasts. GCase RNA in the PS-/- cells was at wild-type levels. Compared with that in wild-type cells (t(1/2) >24 h), the GCase protein in the PS-/- cells had a faster disappearance rate (t(1/2) approximately 1 h in mouse and approximately 8 h in human) as determined by metabolic labeling and immunoprecipitation with anti-GCase antibodies. Treatment of PS-/- cells with leupeptin, an inhibitor of cysteine proteases, led to significant increases (approximately 2-fold) in GCase protein and in vitro activity. Loading saposin C to human PS-/- fibroblasts resulted in an enhancement of GCase protein and in vitro activity. Saposin D loading had no effect. These data indicate that saposin C is required for GCase resistance to proteolytic degradation in the cell. Thus, diminished in vivo GCase activity would be greater than expected only from the lack of GCase activation by saposin C. These results indicate a new property for saposin C, an anti-proteolytic protective function toward GCase.