PALML, a novel paralemmin-related gene mapping on human chromosome 1p21

PALMD haploinsufficiency aggravates extracellular matrix remodeling in vascular smooth muscle cells and promotes calcification

Reduced PALMD expression is strongly associated with the development of calcified aortic valve stenosis; however, the role of PALMD in vascular calcification remains unknown. Calcified arteries were collected from mice to detect PALMD expression. Heterozygous Palmd knockout (Palmd+/-) mice were established to explore the role of PALMD in subtotal nephrectomy-induced vascular calcification. RNA sequencing was applied to detect molecular changes in aortas from Palmd+/- mice. Primary Palmd+/- vascular smooth muscle cells (VSMCs) or PALMD-silenced VSMCs by short interfering RNA were used to analyze PALMD function in phenotypic changes and calcification. PALMD haploinsufficiency aggravated subtotal nephrectomy-induced vascular calcification. RNA sequencing analysis showed that loss of PALMD disturbed the synthesis and degradation of the extracellular matrix (ECM) in aortas, including collagens and matrix metalloproteinases (Col6a6, Mmp2, Mmp9, etc.). In vitro experiments revealed that PALMD-deficient VSMCs were more susceptible to high phosphate-induced calcification. Downregulation of SMAD6 expression and increased levels of p-SMAD2 were detected in Palmd+/- VSMCs, suggesting that transforming growth factor-β signaling may be involved in PALMD haploinsufficiency-induced vascular calcification. Our data revealed that PALMD haploinsufficiency causes ECM dysregulation in VSMCs and aggravates vascular calcification. Our findings suggest that reduced PALMD expression is also linked to vascular calcification, and PALMD may be a potential therapeutic target for this disease. NEW & NOTEWORTHY We found that PALMD haploinsufficiency causes extracellular matrix dysregulation, reduced PALMD expression links to vascular calcification, and PALMD mutations may lead to the risk of both calcific aortic valve stenosis and vascular calcification.

PALMD regulates aortic valve calcification via altered glycolysis and NF-κB-mediated inflammation

Recent genome-wide association and transcriptome-wide association studies have identified an association between the PALMD locus, encoding palmdelphin, a protein involved in myoblast differentiation, and calcific aortic valve disease (CAVD). Nevertheless, the function and underlying mechanisms of PALMD in CAVD remain unclear. We herein investigated whether and how PALMD affects the pathogenesis of CAVD using clinical samples from CAVD patients and a human valve interstitial cell (hVIC) in vitro calcification model. We showed that PALMD was upregulated in calcified regions of human aortic valves and calcified hVICs. Furthermore, silencing of PALMD reduced hVIC in vitro calcification, osteogenic differentiation, and apoptosis, whereas overexpression of PALMD had the opposite effect. RNA-Seq of PALMD-depleted hVICs revealed that silencing of PALMD reduced glycolysis and nuclear factor-κB (NF-κB)–mediated inflammation in hVICs and attenuated tumor necrosis factor α–induced monocyte adhesion to hVICs. Having established the role of PALMD in hVIC glycolysis, we examined whether glycolysis itself could regulate hVIC osteogenic differentiation and inflammation. Intriguingly, the inhibition of PFKFB3-mediated glycolysis significantly attenuated osteogenic differentiation and inflammation of hVICs. However, silencing of PFKFB3 inhibited PALMD-induced hVIC inflammation, but not osteogenic differentiation. Finally, we showed that the overexpression of PALMD enhanced hVIC osteogenic differentiation and inflammation, as opposed to glycolysis, through the activation of NF-κB. The present study demonstrates that the genome-wide association– and transcriptome-wide association–identified CAVD risk gene PALMD may promote CAVD development through regulation of glycolysis and NF-κB–mediated inflammation. We propose that targeting PALMD-mediated glycolysis may represent a novel therapeutic strategy for treating CAVD.

A transcriptome-wide association study identifies PALMD as a susceptibility gene for calcific aortic valve stenosis

Calcific aortic valve stenosis (CAVS) is a common and life-threatening heart disease and the current treatment options cannot stop or delay its progression. A GWAS on 1009 cases and 1017 ethnically matched controls was combined with a large-scale eQTL mapping study of human aortic valve tissues (n = 233) to identify susceptibility genes for CAVS. Replication was performed in the UK Biobank, including 1391 cases and 352,195 controls. A transcriptome-wide association study (TWAS) reveals PALMD (palmdelphin) as significantly associated with CAVS. The CAVS risk alleles and increasing disease severity are both associated with decreased mRNA expression levels of PALMD in valve tissues. The top variant identified shows a similar effect and strong association with CAVS (P = 1.53 × 10⁻¹⁰) in UK Biobank. The identification of PALMD as a susceptibility gene for CAVS provides insights into the genetic nature of this disease, opens avenues to investigate its etiology and to develop much-needed therapeutic options.

Progressive remodeling and calcification of the aortic valve leads to calcific aortic valve stenosis (CAVS) and, ultimately, heart failure. In a combined GWAS and TWAS approach, Thériault et al. identify PALMD as a candidate causal gene for CAVS, which is further supported by Mendelian randomization.

Palmdelphin promotes myoblast differentiation and muscle regeneration

Differentiation of myoblasts is essential in the development and regeneration of skeletal muscles to form multinucleated, contractile muscle fibers. However, the process of myoblast differentiation in mammals is complicated and requires to be further investigated. In this study, we found Palmdelphin (Palmd), a cytosolic protein, promotes myoblast differentiation. Palmd is predominantly expressed in the cytosol of myoblasts and is gradually up-regulated after differentiation. Knockdown of Palmd by small interfering RNA (siRNA) in C2C12 markedly inhibits myogenic differentiation, suggesting a specific role of Palmd in the morphological changes of myoblast differentiation program. Overexpression of Palmd in C2C12 enhances myogenic differentiation. Remarkably, inhibition of Palmd results in impaired myotube formation during muscle regeneration after injury. These findings reveal a new cytosolic protein that promotes mammalian myoblast differentiation and provide new insights into the molecular regulation of muscle formation.

Palmdelphin, a novel target of p53 with Ser46 phosphorylation, controls cell death in response to DNA damage

The tumor suppressor gene p53 regulates apoptosis in response to DNA damage. Promoter selectivity of p53 depends on mainly its phosphorylation. Particularly, the phosphorylation at serine-46 of p53 is indispensable in promoting pro-apoptotic genes that are, however, poorly determined. In the current study, we identified palmdelphin as a pro-apoptotic gene induced by p53 in a phosphorylated serine-46-specific manner. Upregulation of palmdelphin was observed in wild-type p53-transfected cells, but not in serine-46-mutated cells. Expression of palmdelphin was induced by p53 in response to DNA damage. In turn, palmdelphin induced apoptosis. Intriguingly, downregulation of palmdelphin resulted in necroptosis-like cell death via ATP depletion. Upon DNA damage, palmdelphin dominantly accumulated in the nucleus to induce apoptosis. These findings define palmdelphin as a target of serine-46-phosphorylated p53 that controls cell death in response to DNA damage.

Evolution of the vertebrate paralemmin gene family: ancient origin of gene duplicates suggests distinct functions

Paralemmin-1 is a protein implicated in plasma membrane dynamics, the development of filopodia, neurites and dendritic spines, as well as the invasiveness and metastatic potential of cancer cells. However, little is known about its mode of action, or about the biological functions of the other paralemmin isoforms: paralemmin-2, paralemmin-3 and palmdelphin. We describe here evolutionary analyses of the paralemmin gene family in a broad range of vertebrate species. Our results suggest that the four paralemmin isoform genes (PALM1, PALM2, PALM3 and PALMD) arose by quadruplication of an ancestral gene in the two early vertebrate genome duplications. Paralemmin-1 and palmdelphin were further duplicated in the teleost fish specific genome duplication. We identified a unique sequence motif common to all paralemmins, consisting of 11 highly conserved residues of which four are invariant. A single full-length paralemmin homolog with this motif was identified in the genome of the sea lamprey Petromyzon marinus and an isolated putative paralemmin motif could be detected in the genome of the lancelet Branchiostoma floridae. This allows us to conclude that the paralemmin gene family arose early and has been maintained throughout vertebrate evolution, suggesting functional diversification and specific biological roles of the paralemmin isoforms. The paralemmin genes have also maintained specific features of gene organisation and sequence. This includes the occurrence of closely linked downstream genes, initially identified as a readthrough fusion protein with mammalian paralemmin-2 (Palm2-AKAP2). We have found evidence for such an arrangement for paralemmin-1 and -2 in several vertebrate genomes, as well as for palmdelphin and paralemmin-3 in teleost fish genomes, and suggest the name paralemmin downstream genes (PDG) for this new gene family. Thus, our findings point to ancient roles for paralemmins and distinct biological functions of the gene duplicates.

Vesicoureteral reflux

Vesicoureteral reflux (VUR), the retrograde flow of urine from the bladder toward the kidney, is common in young children. About 30% of children with urinary tract infections will be diagnosed with VUR after a voiding cystourethrogram. For most, VUR will resolve spontaneously; 20% to 30% will have further infections, but few will experience long-term renal sequelae. Developmentally, VUR arises from disruption of complex signaling pathways and cellular differentiation. These mechanisms are probably genetically programmed but may be influenced by environmental exposures. Phenotypic expression of VUR is variable, ranging from asymptomatic forms to severe renal parenchymal disease and end-stage disease. VUR is often familial but is genetically heterogeneous with variability in mode of inheritance and in which gene, or the number of genes, that are involved. Numerous genetic studies that explore associations with VUR are available. The relative utility of these for understanding the genetics of VUR is often limited because of small sample size, poor methodology, and a diverse spectrum of patients. Much, if not all, of the renal parenchymal damage associated with end-stage disease is likely to be congenital, which limits the opportunity for intervention to familial cases where risk prediction may be available. Management of children with VUR remains controversial because there is no strong supportive evidence that prophylactic antibiotics or surgical intervention improve outcomes. Furthermore, well-designed genetic epidemiological studies focusing on the severe end of the VUR phenotype may help define the causal pathway and identify modifiable or disease predictive factors.

Vesicoureteric reflux and renal malformations: a developmental problem

Vesicoureteric reflux (VUR) is a congenital urinary tract defect caused by the failure of the ureter to insert correctly into the bladder. It occurs in up to 1% of the general population and is associated with recurrent urinary tract infections and renal failure. Despite treatment of affected children for the past 40 years, the incidence of end-stage renal disease secondary to VUR has not decreased. Twin and family studies reveal that VUR has a genetic basis. Some of the gene candidates that have been identified regulate the position of ureteric budding, a critical step in both kidney and urinary tract development. Analysis of data from humans and mice suggests that some of the renal damage associated with VUR is congenital and is due to a kidney malformation. Therefore, in these cases, the association of VUR and renal failure may be caused by a genetic defect affecting the formation of the kidney and the urinary tract.

Palm is expressed in both developing and adult mouse lens and retina

Background

Paralemmin (Palm) is a prenyl-palmitoyl anchored membrane protein that can drive membrane and process formation in neurons. Earlier studies have shown brain preferred Palm expression, although this protein is a major water insoluble protein in chicken lens fiber cells and the Palm gene may be regulated by Pax6.

Methods

The expression profile of Palm protein in the embryonic, newborn and adult mouse eye as well as dissociated retinal neurons was determined by confocal immunofluorescence. The relative mRNA levels of Palm, Palmdelphin (PalmD) and paralemmin2 (Palm2) in the lens and retina were determined by real time rt-PCR.

Results

In the lens, Palm is already expressed at 9.5 dpc in the lens placode, and this expression is maintained in the lens vesicle throughout the formation of the adult lens. Palm is largely absent from the optic vesicle but is detectable at 10.5 dpc in the optic cup. In the developing retina, Palm expression transiently upregulates during the formation of optic nerve as well as in the formation of both the inner and outer plexiform layers. In short term dissociated chick retinal cultures, Palm protein is easily detectable, but the levels appear to reduce sharply as the cultures age. Palm mRNA was found at much higher levels relative to Palm2 or PalmD in both the retina and lens.

Conclusion

Palm is the major paralemmin family member expressed in the retina and lens and its expression in the retina transiently upregulates during active neurite outgrowth. The expression pattern of Palm in the eye is consistent with it being a Pax6 responsive gene. Since Palm is known to be able to drive membrane formation in brain neurons, it is possible that this molecule is crucial for the increase in membrane formation during lens fiber cell differentiation.

No pathogenic mutations in the uroplakin III gene of 25 patients with primary vesicoureteral reflux

PURPOSE

The uroplakin III (UPIII) knockout mouse provides a good model for human primary vesicoureteral reflux (VUR). Since to our knowledge no causative genes in human VUR have been identified to date, we wondered whether the UPIII gene might be involved in human primary VUR. Therefore, the UPIII gene was sequenced to see if any mutations could be detected in patients with primary VUR.

MATERIALS AND METHODS

DNA was obtained from 25 patients who were surgically treated for primary VUR. Each patient had a family history positive for VUR.

RESULTS

No pathogenic mutations were identified in patient DNA. One missense mutation (Ala154Pro) not reported in the human genome data base was observed. However, because its frequency in the patient and control populations was similar, it was interpreted as a polymorphism.

CONCLUSIONS

Although mutations in regulatory elements affecting gene function cannot be excluded, the UPIII gene does not seem to have a major role in primary VUR in humans.

Screening of gene encoding of hepatic proteins interacting with Hcbp6 via yeast two hybridization

AIM

To seek for hepatic proteins that interacted with protein encoded by Hcbp6 for exploring the biological function of Hcbp6.

METHODS

Hcbp6 gene was introduced into pGBKT7, and then transformed into yeast AH109, which was mated with yeast Y187 (αtype) containing liver cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing x-α-gal. Plasmids were extracted from positive colonies, and sequence analysis was performed by bioinformatics.

RESULTS

Four kind of proteins including paralemmin, Ran binding protein 2, transmembrane transporting protein and albumin were identified to interact with Hcbp6 specifically.

CONCLUSION

Hcbp6 proteins may belong to or be associated with formation of secretary proteins, more study needs to be done for clarifying its biological function.