====== Surfactant protein G ======

The results indicate [[Surfactant protein]] G (SP-G) as a new [[surfactant protein]] which represents an until now unknown surfactant protein class.

Rausch et al. found mRNA for SP-G to be present in kidneys, heart, testis, umbilical cord and trophoblast, 
((Rausch F, Schicht M, Paulsen F, Ngueya I, Bräuer L, Brandt W. "SP-G", a
putative new surfactant protein--tissue localization and 3D structure. PLoS One. 
2012;7(10):e47789. doi: 10.1371/journal.pone.0047789. Epub 2012 Oct 18. PubMed
PMID: 23094088; PubMed Central PMCID: PMC3475697.
)).

[[Surfactant protein]] G was identified by means of [[bioinformatics]] and named surfactant protein G (SP-G) or surfactant-associated protein 2 (SFTA 2) 
((Zhang Z, Henzel WJ (2004) Signal peptide prediction based on analysis of experimentally verified cleavage sites. Protein Sci 13: 2819–2824)).

The protein (SP-G) is encoded on the human chromosome 6, its primary theoretical translation product consist of 78 amino acid residues resulting in a molecular weight of approximately 8 kDa. This putative surfactant protein shows no sequential or structural similarities to surfactant proteins or other known proteins in general and therefore seems to represent a new group of proteins. Furthermore, there is no hard evidence or information neither on the organ or tissue distribution nor on the function of the protein. It is carrying an N-terminal signal peptide of 19 amino acid residues which is essential for protein secretion
((Nakai K (2000) Protein sorting signals and prediction of subcellular localization. Adv Protein Chem 54: 277–344.)).
----
Its presence and possible functions in the central nervous system are unknown. Therefore, a study of  Krause et al., from the Department for Neurosurgery, University Hospital [[Leipzig]], [[Germany]], aimed to elucidate the presence of SP-G in the [[brain]] and its concentration in normal and pathologic samples of [[cerebrospinal fluid]] in order to gain first insight into its regulation and possible functions. A total of 121 samples of human cerebrospinal fluid (30 controls, 60 [[hydrocephalus]] patients, 7 [[central nervous system infection]]s, and 24 [[brain hemorrhage]] patients) and 21 [[rat]] brains were included in the study. 

CSF samples were quantified using a commercially available [[ELISA]] system. Results were analyzed statistically using [[SPSS]] 22, performing Spearman Rho correlation and [[ANOVA]] with Dunnett's post hoc analysis. Rat brains were investigated via [[immunofluorescence]] to determine SP-G presence and colocalization with common markers like [[aquaporin]]-4, [[glial fibrillary acidic protein]], [[platelet and endothelial cell adhesion molecule 1]], and [[neuronal nuclear]] [[antigen]]. SP-G occurs associated with brain [[vessel]]s, comparable to other conventional SPs, and is present in a set of cortical [[neuron]]s. SP-G is furthermore actively produced by ependymal and [[choroid plexus]] [[epithelium]] and secreted into the [[cerebrospinal fluid]]. Its concentrations are low in control subjects and patients suffering from [[aqueductal stenosis]], higher in [[normal pressure hydrocephalus]] (p < 0.01), and highest in [[infection]]s of the central nervous system and brain hemorrhage (p < 0.001). Interestingly, SP-G did correlate with total CSF protein in patients with CNS infections and hemorrhage, but not with cell count. Based on the changes in CSF levels of SP-G in hydrocephalus, brain hemorrhage, and CNS infections as well as its abundance at CSF flow-related anatomical structures closely associated with immunological barrier systems, importance for CSF rheology, brain waste clearance, and host defense is assumable. 

Thus, SP-G is a potential new [[cerebrospinal fluid biomarker]], possibly not only reflecting aspects of CNS innate immune responses, but also rheo-dynamically relevant changes of CSF composition, associated with CSF malabsorbtion. However, further studies are warranted to validate this findings and increase insight into the physiological importance of SP-G in the CNS
((Krause M, Peukert N, Härtig W, Emmer A, Mahr CV, Richter C, Dieckow J, Puchta 
J, Pirlich M, Hoffmann KT, Nestler U, Schob S. Localization, Occurrence, and CSF 
Changes of SP-G, a New Surface Active Protein with Assumable Immunoregulatory
Functions in the CNS. Mol Neurobiol. 2018 Jul 21. doi: 10.1007/s12035-018-1247-x.
[Epub ahead of print] PubMed PMID: 30032421.
)).
===== References =====