Lafora disease: from genotype to phenotype

The progressive myoclonic epilepsy of Lafora or Lafora disease (LD) is a neurodegenerative disorder characterized by recurrent seizures and cognitive deficits. With typical onset in the late childhood or early adolescence, the patients show progressive worsening of the disease symptoms, leading to death in about 10 years. It is an autosomal recessive disorder caused by the loss-of-function mutations in the EPM2A gene, coding for a protein phosphatase (laforin) or the NHLRC1 gene coding for an E3 ubiquitin ligase (malin). LD is characterized by the presence of abnormally branched water insoluble glycogen inclusions known as Lafora bodies in the neurons and other tissues, suggesting a role for laforin and malin in glycogen metabolic pathways. Mouse models of LD, developed by targeted disruption of the Epm2a or Nhlrc1 gene, recapitulated most of the symptoms and pathological features as seen in humans, and have offered insight into the pathomechanisms. Besides the formation of Lafora bodies in the neurons in the presymptomatic stage, the animal models have also demonstrated perturbations in the proteolytic pathways, such as ubiquitin-proteasome system and autophagy, and inflammatory response. This review attempts to provide a comprehensive coverage on the genetic defects leading to the LD in humans, on the functional properties of the laforin and malin proteins, and on how defects in any one of these two proteins result in a clinically similar phenotype. We also discuss the disease pathologies as revealed by the studies on the animal models and, finally, on the progress with therapeutic attempts albeit in the animal models.     

Differential reduction of reactive oxygen species by human tissue-specific mesenchymal stem cells from different donors under oxidative stress

Clinical trials using human Mesenchymal Stem Cells (MSCs) have shown promising results in the treatment of various diseases. Different tissue sources, such as bone marrow, adipose tissue, dental pulp and umbilical cord, are being routinely used in regenerative medicine. MSCs are known to reduce increased oxidative stress levels in pathophysiological conditions. Differences in the ability of MSCs from different donors and tissues to ameliorate oxidative damage have not been reported yet. In this study, for the first time, we investigated the differences in the reactive oxygen species (ROS) reduction abilities of tissue-specific MSCs to mitigate cellular damage in oxidative stress. Hepatic Stellate cells (LX-2) and cardiomyocytes were treated with Antimycin A (AMA) to induce oxidative stress and tissue specific MSCs were co-cultured to study the reduction in ROS levels. We found that both donor’s age and source of tissue affected the ability of MSCs to reduce increased ROS levels in damaged cells. In addition, the abilities of same MSCs differed in LX-2 and cardiomyocytes in terms of magnitude of reduction of ROS, suggesting that the type of recipient cells should be kept in consideration when using MSCs in regenerative medicine for treatment purposes.     

Design, synthesis and pharmacological evaluation of novel tetrasubstituted thiophene analogues as anti-inflammatory agents

A new series of tetrasubstituted thiophene analogues (4a-4f, 5a-5f and 8a-8i) were designed incorporating the pharmacophoric features of COX-1 (as in fenamates), 5-LOX and the p38 MAP kinase inhibitors. The designed series was synthesized by nucleophilic addition of aryl/aroylisothiocyanate and enamine (2) yielding the addition product l-(alpha-Carbomethoxy-beta-aminothiocrotonoyl)-aryl/aroyl amines (3/7); which on reaction with substituted phenacyl bromides gave the targeted tetrasubstituted thiophene esters (4a-4f / 8a-8i). The tetrasubstituted thiophenes esters (4a-4f ) on hydrolysis with one equivalent of potassium hydroxide solution in methanol at room temperature gave corresponding acids (5a-5f ). All the targeted compounds were evaluated for their anti-inflammatory activity in carrageenin-induced rat hind paw oedema model at the doses of 10, 20 and 40 mg/kg body weight using standard drugs mefanamic acid and ibuprofen. The compounds (4c, 4e, 4f, 5f, 8a- 8i) which gave reasonable protection to the inflamed paw, eliciting good or moderate comparable anti-inflammatory activity were selected for investigating their analgesic activity using acetic acid induced writhing response test in albino mice at 10 mg/kg dose using standard drug ibuprofen and in order to arrive at possible mechanism of their anti-inflammatory activity, in vitro antioxidant nitric oxide radical scavenging assay at the concentrations of 5, 10, 15, 20, 25, 30 and 35 microg/mL were performed using standard drug ascorbic acid.     

Characterization of resistance mechanism in transgenic Nicotiana benthamiana containing Turnip crinkle virus coat protein

Two transgenic lines, of Nicotiana benthamiana expressing Turnip crinkle virus (TCV)-coat protein (CP) gene with contrasting phenotype, the highest (#3) and the lowest (#18) CP expressers, were selected and challenged with the homologous TCV. The former, the highest expresser, showed nearly five times more CP expression than the latter. Progenies of #3 and #18 lines showed 30 and 100% infection rates, respectively. The infected progenies of #3 line showed mild and delayed symptom with TCV. This is a coat protein-mediated resistance (CP-MR), and its resistance level is directly proportional to CP transgene expression. However, CP-MR of the transgenic plants was specific only for TCV but not for heterologous viruses. Newly growing leaves of those infected progenies of #3 line did not show any visible symptoms at 4-week post-inoculation (wpi) with TCV, suggesting a reversal from infection. This was confirmed by RT-PCR analysis with the disappearance of the target at 4 wpi. This is a case of RNA-mediated resistance, and a threshold level of transgene expression may be needed to achieve the silent state. To confirm the RNA silencing, we infiltrated Agrobacterium carrying TCV-CP into leaves of progenies of #3 and performed RT-PCR analysis. The results indicate that TCV-CP’s suppressor activity against RNA silencing itself can be silenced by the homologous expression of TCV-CP in the transgenic plants. The transgenic plants containing TCV-CP seem to be a model system to study viral protection mediated by a combination of protein and RNA silencing. Ayyappan Vasudevan and Tae-Kyun Oh have contributed equally in this study.     

Tomato transcriptional changes in response to Clavibacter michiganensis subsp. michiganensis reveal a role for ethylene in disease development

Clavibacter michiganensis subsp. michiganensis (Cmm) is a gram-positive actinomycete, causing bacterial wilt and canker disease in tomato (Solanum lycopersicum). Host responses to gram-positive bacteria and molecular mechanisms associated with the development of disease symptoms caused by Cmm in tomato are largely unexplored. To investigate plant responses activated during this compatible interaction, we used microarray analysis to monitor changes in host gene expression during disease development. This analysis was performed at 4 d postinoculation, when bacteria were actively multiplying and no wilt symptoms were yet visible; and at 8 d postinoculation, when bacterial growth approached saturation and typical wilt symptoms were observed. Of the 9,254 tomato genes represented on the array, 122 were differentially expressed in Cmm-infected plants, compared with mock-inoculated plants. Functional classification of Cmm-responsive genes revealed that Cmm activated typical basal defense responses in the host, including induction of defense-related genes, production and scavenging of free oxygen radicals, enhanced protein turnover, and hormone synthesis. Cmm infection also induced a subset of host genes involved in ethylene biosynthesis and response. After inoculation with Cmm, Never ripe (Nr) mutant plants, impaired in ethylene perception, and transgenic plants with reduced ethylene synthesis showed significant delay in the appearance of wilt symptoms, compared with wild-type plants. The retarded wilting in Nr plants was a specific effect of ethylene insensitivity, and was not due to altered expression of defense-related genes, reduced bacterial populations, or decreased ethylene synthesis. Taken together, our results indicate that host-derived ethylene plays an important role in regulation of the tomato susceptible response to Cmm.     

Activation and manipulation of host responses by a Gram-positive bacterium

The interaction between tomato plants and Clavibacter michiganensis subsp. michiganensis (Cmm) represents a model pathosystem to study the interplay between the virulence determinants of a Gram-positive bacterium and the attempt of a crop plant to counteract pathogen invasion. To investigate plant responses activated during this compatible interaction, we recently analyzed gene expression profiles of tomato stems infected with Cmm. This analysis revealed activation of basal defense responses that are typically observed upon plant perception of pathogen-associated molecular patterns. In addition, Cmm infection upregulated the expression of host genes related to ethylene synthesis and response. Further analysis of tomato plants impaired in ethylene perception and production demonstrated an important role for ethylene in the development of disease symptoms. Here we discuss possible molecular strategies used by the plant to recognize Cmm infection and possible mechanisms employed by the pathogen to interfere with the activation of plant defense responses and promote disease.Key words: tomato, Clavibacter michiganensis subsp. michiganensis, ethylene, basal defense, pathogen-associated molecular patternsLittle is known on the strategies employed by Gram-positive phytopathogenic bacteria to sense the presence of the host plant, penetrate and colonize tissue, and counteract plant defense responses. Also largely unexplored are the molecular mechanisms associated with detection of Gram-positive bacteria by the host plant and with the activation of attempted defense responses.Among the most devastating Gram-positive disease agents are actinobacteria of the genus Clavibacter whose subspecies cause systemic infections of the xylem in different plant species.¹ The subspecies Clavibacter michiganensis subsp. michiganensis (Cmm) causes bacterial wilt and canker of tomato (Solanum lycopersicum), an economically important disease causing yield losses worldwide.¹ In recent years important insight into the molecular mechanism of Cmm pathogenicity has been achieved,¹ and genome sequence of a Cmm strain has been established.² Major Cmm pathogenicity determinants are plasmid borne and include the β-1,4-endocellulase CelA,³ and the putative serine protease Pat-1.⁴ Additional genes important for virulence are located in a pathogenicity island of about 129 kb on the Cmm chromosome which has a relatively low G + C content and is required for effective Cmm colonization of tomato plants.²Tomato is an economically important crop amenable to genetic analysis and transformations. Many resources are available for this plant species, including germplasm collections, natural and induced mutants, an extensive expressed sequence tag database and an ongoing genome sequencing project.⁵ In addition, because of its experimental tractability, tomato plants have been widely used to study plant disease resistance and susceptibility. As genetic and molecular tools for both Cmm and tomato are in place, the tomato-Cmm pathosystem represents an excellent model to study the interplay between virulence determinants of a Gram-positive phytopathogenic bacterium and defense responses of a crop plant.To get insight into host responses occurring during the tomato-Cmm compatible interaction and molecular mechanisms associated with the development of wilt and canker disease symptoms, we recently analyzed gene expression profiles of tomato stems infected with Cmm.⁶ This analysis revealed a clear activation of basal defense responses, which are typically observed upon plant perception of pathogen-associated molecular patterns (PAMPs).⁷ These include production and scavenging of free oxygen radicals, induction of defense-related genes, enhanced protein turnover, and hormone biosynthesis. Interestingly, several tomato genes encoding proteins with characteristics of cell-surface receptors were differentially expressed in response to Cmm infection.⁶ These proteins can be considered as candidate receptors for Cmm PAMPs and include two receptor-like kinases, a homolog of the receptor for the fungal PAMP ethylene-inducing xylanase from Trichoderma viride,⁸ and the Ve1 resistance protein, which confers resistance in tomato to the vascular disease Verticillium wilt.⁹It remains to be elucidated what are the Cmm PAMPs perceived by tomato plants. Cold-shock protein from Gram-positive bacteria and different microbial patterns of Gram-negative bacteria, including lipopolysaccharides, flagellin, and the translational elongation factor EF-TU, were shown to act as PAMPs in plants.¹⁰ Similarly, Cmm cold shock protein or cell wall components, such as peptidoglycan, lipoteichoic acid, and lipopeptides, which function as Gram positive-derived PAMPs in animal systems¹¹, may act as PAMPs during the tomato-Cmm interaction. Additional possible Cmm PAMPs are exopolysaccharides, which are produced in large amounts by the bacterium and may interact directly with surface-exposed plant proteins.¹ The numerous extracellular cell wall degrading enzymes secreted by Cmm may also function as PAMPs, as observed for the fungal ethylene-inducing xylanase.^2,12 Alternatively, by virtue of their hydrolytic activity, these enzymes may release plant cell wall fragments that are recognized by PAMP receptors. Indeed, different β-glucan fragments released from plant cell walls were shown to elicit plant basal defense responses.^13,14How Cmm copes with the activation of basal defense responses is largely unknown. Many potential virulence determinants that might interfere with the plant defense reaction are clustered in the Cmm pathogenicity island, which is essential for effective plant colonization.² Several extracellular serine proteases are encoded in this region and inactivation of part of them by gene replacement drastically reduced Cmm colonization of tomato plants.² Although their targets are still unknown, these proteins might interfere with plant signaling pathways as it was described for certain cysteine proteases that serves in Gram-negative bacteria as suppressors of plant defenses.¹⁵ An additional candidate for interference with plant signaling may be a tomatinase, also encoded in the Cmm pathogenicity island, because hydrolysis products of α-tomatine were shown to suppress plant defense responses in a fungal system.¹⁶In addition to detecting the activation of basal defense responses, host gene expression profiling during the tomato-Cmm interaction unraveled the involvement of ethylene in disease development.⁶ In fact, Cmm infection of tomato stems was found to induce expression of host genes related to ethylene biosynthesis and response (Fig. 1).⁶ Further analysis of ethylene-insensitive Never ripe mutants and transgenic plants with reduced ethylene synthesis indicated that ethylene is required for normal development of wilting symptoms (Fig. 2), but not for the activation of defense-related genes or bacterial colonization.⁶ We hypothesize that during infection ethylene synthesis and response are manipulated by Cmm virulence determinants to promote disease. Alternatively, ethylene is released as part of the host responses activated by bacterial recognition, or as a result of tissue maceration. In line with our first hypothesis, the type III effectors AvrPto and AvrPtoB from Pseudomonas syringae pv. tomato were shown to promote enhanced disease symptoms in tomato leaves, in part, by upregulating genes involved in ethylene production.¹⁷ Interestingly, expression in tomato plants of AvrPto or AvrPtoB, and infection with Cmm resulted in the upregulation of the SlACO1 gene encoding the key enzyme of ethylene biosynthesis ACC oxidase.^6,17Open in a separate windowFigure 1Kinetics of ACC oxidase (ACO) gene expression in tomato plants inoculated with Cmm. Six-week-old tomato plants were infected with a Cmm suspension (10⁸ cfu/ml) or mock-inoculated. Total RNA was extracted from stem samples harvested at the indicated day post-inoculation (dpi) and subjected to Northern blot analysis using as probe a 550 bp fragment of the SlACO1 gene, which shares high homology with other ACO family members (upper). Ethidium bromide staining shows the amount of RNA loaded in each lane (lower).Open in a separate windowFigure 2Effect of impaired ethylene sensitivity on development of wilt symptoms in tomato plants infected with Cmm. Six-week-old plants were infected with a Cmm suspension (10⁸ cfu/ml) and examined for development of wilt symptoms during a 20-day period. The percentage of plants showing wilt symptoms was calculated in a group of at least 30 plants for the ethylene-insensitive mutant Never ripe and wild-type Pearson plants. Data are representative of two independent experiments.In conclusion, future research challenges for understanding how host responses are regulated by the plant and manipulated by a Gram-positive bacterium will be the isolation of Cmm PAMPs and their plant receptors, the identification of Cmm virulence determinants and the elucidation of their mode of action.     

Patterning of diverse mammalian cell types in serum free medium with photoablation

Integration of living cells with novel microdevices requires the development of innovative technologies for manipulating cells. Chemical surface patterning has been proven as an effective method to control the attachment and growth of diverse cell populations. Patterning polyelectrolyte multilayers through the combination of layer‐by‐layer self‐assembly technique and photolithography offer a simple, versatile, and silicon compatible approach that overcomes chemical surface patterning limitations, such as short‐term stability and low‐protein adsorption resistance. In this study, direct photolithographic patterning of two types of multilayers, PAA (poly acrylic acid)/PAAm (poly acryl amide) and PAA/PAH (poly allyl amine hydrochloride), were developed to pattern mammalian neuronal, skeletal, and cardiac muscle cells. For all studied cell types, PAA/PAAm multilayers behaved as a cytophobic surface, completely preventing cell attachment. In contrast, PAA/PAH multilayers have shown a cell‐selective behavior, promoting the attachment and growth of neuronal cells (embryonic rat hippocampal and NG108‐15 cells) to a greater extent, while providing little attachment for neonatal rat cardiac and skeletal muscle cells (C2C12 cell line). PAA/PAAm multilayer cellular patterns have also shown a remarkable protein adsorption resistance. Protein adsorption protocols commonly used for surface treatment in cell culture did not compromise the cell attachment inhibiting feature of the PAA/PAAm multilayer patterns. The combination of polyelectrolyte multilayer patterns with different adsorbed proteins could expand the applicability of this technology to cell types that require specific proteins either on the surface or in the medium for attachment or differentiation, and could not be patterned using the traditional methods. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Homologues of the Bacillus subtilis SpoVB Protein Are Involved in Cell Wall Metabolism

Members of the COG2244 protein family are integral membrane proteins involved in synthesis of a variety of extracellular polymers. In several cases, these proteins have been suggested to move lipid-linked oligomers across the membrane or, in the case of Escherichia coli MviN, to flip the lipid II peptidoglycan precursor. Bacillus subtilis SpoVB was the first member of this family implicated in peptidoglycan synthesis and is required for spore cortex polymerization. Three other COG2244 members with high similarity to SpoVB are encoded within the B. subtilis genome. Mutant strains lacking any or all of these genes (yabM, ykvU, and ytgP) in addition to spoVB are viable and produce apparently normal peptidoglycan, indicating that their function is not essential in B. subtilis. Phenotypic changes associated with loss of two of these genes suggest that they function in peptidoglycan synthesis. Mutants lacking YtgP produce long cells and chains of cells, suggesting a role in cell division. Mutants lacking YabM exhibit sensitivity to moenomycin, an antibiotic that blocks peptidoglycan polymerization by class A penicillin-binding proteins. This result suggests that YabM may function in a previously observed alternate pathway for peptidoglycan strand synthesis.The Bacillus subtilis spoVB gene was first identified as a locus in which a mutation could produce a block at a late stage of spore development (14, 30). Analysis of this locus revealed that it encoded an apparent integral membrane protein (33), and a detailed analysis of a spoVB null mutant demonstrated a block at a very early step in synthesis of the spore cortex peptidoglycan (PG) (40). The mutant synthesized essentially no cortex and accumulated cytoplasmic PG precursors, the same phenotype found in other mutant strains blocked in functions known to be directly involved in PG polymerization (40). These results suggested that SpoVB plays a direct role in assembly or function of the spore PG synthesis apparatus.PG synthesis is a highly conserved and complex process that must span the cell membrane (reviewed in reference 38). Soluble nucleotide-linked PG precursors are synthesized in the cytoplasm. N-Acetylmuramic acid with a pentapeptide side chain is then transferred to an undecaprenol lipid carrier to produce lipid I, with subsequent addition of N-acetylglucosamine to produce lipid II, undecaprenyl-pyrophosphoryl-N-acetylmuramic acid (pentapeptide)-N-acetylglucosamine. Lipid II is then flipped across the membrane via an unknown mechanism. Two families of proteins have been postulated to perform this function: the SEDS family of integral membrane proteins, including FtsW, RodA, and SpoVE (13), and, more recently, the COG2244 family (23), which includes SpoVB and the MviN (MurJ) protein of Escherichia coli (35). In both cases, loss of a protein within one of these families has been shown to result in a block in PG synthesis and the accumulation of lipid-linked and/or soluble PG precursors (16, 20, 35, 40).In the standard model of PG synthesis, flippase activity brings the disaccharide-pentapeptide moieties to the penicillin-binding proteins (PBPs), which polymerize the PG macromolecule on the outer surface of the membrane (39). The class A, high-molecular-weight PBPs possess an N-terminal glycosyl transferase domain that polymerizes the disaccharides into polysaccharide chains (38). These chains are cross-linked via the transpeptidase activity within the penicillin-binding, C-terminal domains of both the class A and the class B PBPs. The N-terminal domains of the class A PBPs and the closely related monofunctional glycosyl transferases found in some species are the only defined PG glycan strand polymerases, and in several species the presence of at least one of these enzymes is essential. However, in B. subtilis (26) and Enterococcus faecalis (3), strains lacking all of these known glycosyl transferases are viable and produce PG walls, indicating the presence of another glycosyl transferase capable of this activity. This alternate glycosyl transferase is distinct in that it is relatively resistant to moenomycin (3, 26), an inhibitor of the class A PBP glycosyl transferase activity (6).Given the strong and early block in cortex PG polymerization observed to occur in a spoVB mutant (40), we wished to further analyze the potential role of this class of protein. SpoVB is a member of a relatively large family of proteins, COG2244 (23), some of which are involved in polymerization of other polysaccharides in bacteria, archaea, and eukaryotes. Bioinformatic analysis has generally predicted that these proteins span the membrane 12 to 14 times, and in some cases experimental evidence has supported this structure (7, 24). A role generally ascribed to these proteins is the flipping of lipid-linked oligosaccharides, produced on the inner face of a membrane, to the outside, where the oligosaccharides are then further polymerized or transferred to other substrates. Some prominent members of this family include Wzx, which functions in O-antigen synthesis in gram-negative bacteria (41); TuaB, which functions in teichuronic acid synthesis in B. subtilis (36); and Rft1, which functions in protein glycosylation in eukaryotes (12). MviN is essential in some gram-negative species, including Burkholderia pseudomallei, E. coli, and Sinorhizobium meliloti (22, 34), and has been shown to play a role in E. coli PG synthesis (16, 35). A Rhizobium tropici mutation that truncates mviN approximately 50% into the coding sequence was not lethal (29). However, it is not known whether this was the sole mviN homolog in the genome or whether the truncated gene product might be functional.We have analyzed the phenotypic properties of B. subtilis strains lacking other proteins within the COG2244 family that are most closely related to SpoVB. Results suggest that these proteins also play roles in PG synthesis and that, in one case, this role is in a synthetic system that is relatively moenomycin resistant. We postulate that these proteins function in an alternate pathway for PG synthesis that may involve the flipping of lipid-linked PG oligosaccharides rather than lipid II disaccharides.