Skipped BSCL2 Transcript in Celia's Encephalopathy (PELD): New Insights on Fatty Acids Involvement, Senescence and Adipogenesis

OBJECTIVE

PELD (Progressive Encephalopathy with or without Lipodystrophy or Celia's Encephalopathy) is a fatal and rare neurodegenerative syndrome associated with the BSCL2 mutation c.985C>T, that results in an aberrant transcript without the exon 7 (Celia seipin). The aim of this study was to evaluate both the process of cellular senescence and the effect of unsaturated fatty acids on preadipocytes from a homozygous c.985C>T patient. Also, the role of aberrant seipin isoform on adipogenesis was studied in adipose-derived human mesenchymal stem cells.

MATERIAL AND METHODS

Cellular senescence was evaluated using β-galactosidase staining of preadipocytes obtained from a homozygous c.985C>T patient. Moreover, these cells were cultured during 24 hours with Intralipid, a soybean oil-based commercial lipid emulsion. The expression of the different BSCL2 transcripts was measured by qPCR. Adipose-derived human mesenchymal stem cells were differentiated to a fat lineage using StemPRO adipogenesis kit, and the expression of BSCL2 transcripts and several adipogenesis-related genes was measured by qPCR.

RESULTS

the treatment of preadipocytes with unsaturated fatty acids significantly reduced the expression of the BSCL2 transcript without exon 7 by 34 to 63%. On the other hand, at least in preadipocytes, this mutation does not disturb cellular senescence rate. Finally, during adipocyte differentiation of adipose-derived human mesenchymal stem cells, the expression of adipogenic genes (PPARG, LPIN1, and LPL) increased significantly over 14 days, and noteworthy is that the BSCL2 transcript without exon 7 was differentially expressed by 332 to 723% when compared to day 0, suggesting an underlying role in adipogenesis.

CONCLUSIONS

our results suggest that Celia seipin is probably playing an underestimated role in adipocyte maturation, but not in senescence, and its expression can be modified by exogenous factors as fatty acids.

Signaling specificity provided by the Arabidopsis thaliana heterotrimeric G-protein γ subunits AGG1 and AGG2 is partially but not exclusively provided through transcriptional regulation

The heterotrimeric G-protein complex in Arabidopsis thaliana consists of one α, one ß and three γ subunits. While two of the γ subunits, AGG1 and AGG2 have been shown to provide functional selectivity to the Gßγ dimer in Arabidopsis, it is unclear if such selectivity is embedded in their molecular structures or conferred by the different expression patterns observed in both subunits. In order to study the molecular basis for such selectivity we tested genetic complementation of AGG1- and AGG2 driven by the respectively swapped gene promoters. When expressed in the same tissues as AGG1, AGG2 rescues some agg1 mutant phenotypes such as the hypersensitivity to Fusarium oxysporum and D-mannitol as well as the altered levels of lateral roots, but does not rescue the early flowering phenotype. Similarly, AGG1 when expressed in the same tissues as AGG2 rescues the osmotic stress and lateral-root phenotypes observed in agg2 mutants but failed to rescue the heat-stress induction of flowering. The fact that AGG1 and AGG2 are functionally interchangeable in some pathways implies that, at least for those pathways, signaling specificity resides in the distinctive spatiotemporal expression patterns exhibited by each γ subunit. On the other hand, the lack of complementation for some phenotypes indicates that there are pathways in which signaling specificity is provided by differences in the primary AGG1 and AGG2 amino acid sequences.

Overexpression of a short human seipin/BSCL2 isoform in mouse adipose tissue results in mild lipodystrophy

Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is a recessive disorder characterized by an almost complete loss of adipose tissue, insulin resistance, and fatty liver. BSCL2 is caused by loss-of-function mutations in the BSCL2/seipin gene, which encodes seipin. The essential role for seipin in adipogenesis has recently been established both in vitro and in vivo. However, seipin is highly upregulated at later stages of adipocyte development, and its role in mature adipocytes remains to be elucidated. We therefore generated transgenic mice overexpressing a short isoform of human BSCL2 gene (encoding 398 amino acids) using the adipocyte-specific aP2 promoter. The transgenic mice produced ∼150% more seipin than littermate controls in white adipose tissue. Surprisingly, the increased expression of seipin markedly reduced the mass of white adipose tissue and the size of adipocytes and lipid droplets. This may be due in part to elevated lipolysis rates in the transgenic mice. Moreover, there was a nearly 50% increase in the triacylglycerol content of transgenic liver. These results suggest that seipin promotes the differentiation of preadipocytes but may inhibit lipid storage in mature adipocytes.

Sexual dimorphism of G-protein subunit Gng13 expression in the cortical region of the developing mouse ovary

In our search for genes required for the development and function of mouse gonads, we identified Gng13 (guanine nucleotide binding protein 13, gamma), a gene with an embryonic expression pattern highly restricted to the ovary. Based on reverse transcriptase-polymerase chain reaction (RT-PCR) and whole-mount in situ hybridization, Gng13 is expressed in both XX and XY gonads at embryonic day (E) 11.5, but becomes up-regulated in the XX gonad by E12.5. Expression is retained after treatment with busulfan, a chemical known to eliminate germ cells, pointing to the soma as a site of Gng13 transcription. In situ hybridization of embryonic ovarian tissue sections further localized the expression to the cortex of the developing XX gonad. Gng13 expression in the adult is also highly restricted. Northern blot analyses and Genomic Institute of the Novartis Research Foundation expression profiling of adult tissues detected very high expression in the cerebrum and cerebellum, in addition to, a weaker signal in the ovary. Gng13 belongs to a well-known family of signal transduction molecules with functions in many aspects of development and organ physiology. Here, we report that, in the developing mouse embryo, expression of Gng13 mRNA is highly restricted to the cortex of the XX gonad during sexual differentiation, suggesting a role for this gene during ovarian development.

Assembly and trafficking of heterotrimeric G proteins

To be activated by cell surface G protein-coupled receptors, heterotrimeric G proteins must localize at the cytoplasmic surface of plasma membranes. Moreover, some G protein subunits are able to traffic reversibly from the plasma membrane to intracellular locations upon activation. This current topic will highlight new insights into how nascent G protein subunits are assembled and how they arrive at plasma membranes. In addition, recent reports have increased our knowledge of activation-induced trafficking of G proteins. Understanding G protein assembly and trafficking will lead to a greater understanding of novel ways that cells regulate G protein signaling.

Dopamine Receptor-interacting Protein 78 Acts as a Molecular Chaperone for Gγ Subunits before Assembly with Gβ

Heterotrimeric G proteins play a central role in intracellular communication mediated by extracellular signals, and both Galpha and Gbetagamma subunits regulate effectors downstream of activated receptors. The particular constituents of the G protein heterotrimer affect both specificity and efficiency of signal transduction. However, little is known about mechanistic aspects of G protein assembly in the cell that would certainly contribute to formation of heterotrimers of specific composition. It was recently shown that phosducin-like protein (PhLP) modulated both Gbetagamma expression and subsequent signaling by chaperoning nascent Gbeta and facilitating heterodimer formation with Ggamma subunits (Lukov, G. L., Hu, T., McLaughlin, J. N., Hamm, H. E., and Willardson, B. M. (2005) EMBO J. 24, 1965-1975; Humrich, J., Bermel, C., Bunemann, M., Harmark, L., Frost, R., Quitterer, U., and Lohse, M. J. (2005) J. Biol. Chem. 280, 20042-20050). Here we demonstrate using a variety of techniques that DRiP78, an endoplasmic reticulum resident protein known to regulate the trafficking of several seven transmembrane receptors, interacts specifically with the Ggamma subunit but not Gbeta or Galpha subunits. Furthermore, we demonstrate that DRiP78 and the Gbeta subunit can compete for the Ggamma subunit. DRiP78 also protects Ggamma from degradation until a stable partner such as Gbeta is provided. Furthermore, DRiP78 interaction may represent a mechanism for assembly of specific Gbetagamma heterodimers, as selectivity was observed among Ggamma isoforms for interaction with DRiP78 depending on the presence of particular Gbeta subunits. Interestingly, we could detect an interaction between DRiP78 and PhLP, suggesting a role of DRiP78 in the assembly of Gbetagamma by linking Ggamma to PhLP.Gbeta complexes. Our results, therefore, suggest a role of DRiP78 as a chaperone in the assembly of Gbetagamma subunits of the G protein.

A2A adenosine-receptor-mediated facilitation of noradrenaline release in rat tail artery involves protein kinase C activation and betagamma subunits formed after alpha2-adrenoceptor activation

This work aimed to investigate the molecular mechanisms involved in the interaction of alpha2-adrenoceptors and adenosine A2A-receptor-mediated facilitation of noradrenaline release in rat tail artery, namely the type of G-protein involved in this effect and the step or steps where the signalling cascades triggered by alpha2-adrenoceptors and A2A-receptors interact. The selective adenosine A2A-receptor agonist 2-p-(2-carboxy ethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680; 100 nM) enhanced tritium overflow evoked by trains of 100 pulses at 5 Hz. This effect was abolished by the selective adenosine A2A-receptor antagonist 5-amino-7-(2-phenyl ethyl)-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo [1,5-c]pyrimidine (SCH 58261; 20 nM) and by yohimbine (1 microM). CGS 21680-mediated effects were also abolished by drugs that disrupted G(i/o)-protein coupling with receptors, PTX (2 microg/ml) or NEM (40 microM), by the anti-G(salpha) peptide (2 microg/ml) anti-G(betagamma) peptide (10 microg/ml) indicating coupling of A2A-receptors to G(salpha) and suggesting a crucial role for G(betagamma) subunits in the A(2A)-receptor-mediated enhancement of tritium overflow. Furthermore, phorbol 12-myristate 13-acetate (PMA; 1 microM) or forskolin (1 microM), direct activators of protein kinase C and of adenylyl cyclase, respectively, also enhanced tritium overflow. In addition, PMA-mediated effects were not observed in the presence of either yohimbine or PTX. Results indicate that facilitatory adenosine A2A-receptors couple to G(salpha) subunits which is essential, but not sufficient, for the release facilitation to occur, requiring the involvement of G(i/o)-protein coupling (it disappears after disruption of G(i/o)-protein coupling, PTX or NEM) and/or G(betagamma) subunits (anti-G(betagamma)). We propose a mechanism for the interaction in study suggesting group 2 AC isoforms as a plausible candidate for the interaction site, as these isoforms can integrate inputs from G(salpha) subunits (released after adenosine A2A-receptor activation; prime-activation), G(betagamma) subunits (released after activation of G(i/o)-protein coupled receptors) which can directly synergistically stimulate the prime-activated AC or indirectly via G(betagamma) activation of the PLC-PKC pathway.