Pla2g12b drives expansion of triglyceride-rich lipoproteins.

Vertebrates transport hydrophobic triglycerides through the circulatory system by packaging them within amphipathic particles called Triglyceride-Rich Lipoproteins. Yet, it remains largely unknown how triglycerides are loaded onto these particles. Mutations in Phospholipase A2 group 12B (PLA2G12B) are known to disrupt lipoprotein homeostasis, but its mechanistic role in this process remains unclear. Here we report that PLA2G12B channels lipids within the lumen of the endoplasmic reticulum into nascent lipoproteins. This activity promotes efficient lipid secretion while preventing excess accumulation of intracellular lipids. We characterize the functional domains, subcellular localization, and interacting partners of PLA2G12B, demonstrating that PLA2G12B is calcium-dependent and tightly associated with the membrane of the endoplasmic reticulum. We also detect profound resistance to atherosclerosis in PLA2G12B mutant mice, suggesting an evolutionary tradeoff between triglyceride transport and cardiovascular disease risk. Here we identify PLA2G12B as a key driver of triglyceride incorporation into vertebrate lipoproteins.

MicroRNA-541-3p alters lipoproteins to reduce atherosclerosis by degrading Znf101 and Casz1 transcription factors.

High apoB-containing low-density lipoproteins (LDL) and low apoA1-containing high-density lipoproteins (HDL) are associated with atherosclerosis. In search of a molecular regulator that could simultaneously and reciprocally control both LDL and HDL levels, we screened a microRNA (miR) library using human hepatoma Huh-7 cells. We identified miR-541-3p that both decreases apoB and increases apoA1 expression by inducing mRNA degradation of two different transcription factors, Znf101 and Casz1. Znf101 enhances apoB expression while Casz1 represses apoA1 expression. The hepatic knockdown of orthologous Zfp961 and Casz1 genes in mice altered plasma lipoproteins and reduced atherosclerosis without causing hepatic lipid accumulation, most likely by lowering hepatic triglyceride production, increasing HDL cholesterol efflux capacity, and reducing lipogenesis. Notably, human genetic variants in the MIR541, ZNF101, and CASZ1 loci are significantly associated with plasma lipids and lipoprotein levels. This study identifies miR-541-3p and Znf101/Casz1 as potential therapeutic agent and targets, respectively, to reduce plasma lipoproteins and atherosclerosis without causing liver steatosis.

Symbiotic dynamics in living liquid crystals.

An amalgam of nematic liquid crystals and active matter, referred to as living liquid crystals, is a promising self-healing material with futuristic applications for targeted delivery of information and microcargo. We provide a phenomenological model to study the symbiotic pattern dynamics in this contemporary system using the Toner-Tu model for active matter (AM), the Landau-de Gennes free energy for liquid crystals (LCs), and an experimentally motivated coupling term that favours coalignment of the active and nematic components. Our extensive theoretical studies unfold two novel steady states, chimeras and solitons, with sharp regions of distinct orientational order that sweep through the coupled system in synchrony. The induced dynamics in the passive nematic is unprecedented. We show that the symbiotic dynamics of the AM and LC components can be exploited to induce and manipulate order in an otherwise disordered system.

Nonlinear energy dissipation and transfers in coarsening systems.

During coarsening, small structures disappear, leaving behind only large ones. Here we study the spectral energy transfers in Model A, where the order parameter ϕ evolves via nonconserved dynamics. We show that the nonlinear interactions dissipate fluctuations and facilitate energy transfers among the Fourier modes so that only ϕ(k=0), where k is the wave number, survives at the end and approaches the asymptotic value +1 or -1. We contrast the coarsening evolution for the initial conditions with 〈ϕ(x,t=0)〉=0 and with uniformly positive or negative ϕ(x,t=0).

Modulations of functional traits of Spinacia oleracea plants exposed to cadmium stress by using H2S as an antidote: a regulatory mechanism.

The present study is based on the application of H2S as an exogenous antidote in Spinacia oleracea (spinach) plants grown in Cd-contaminated (50 ppm) soil. The different doses of H2S in the form of NaHS (10, 50, 100, 200, and 500 µM) have been applied as a foliar spray to regulate the physiological attributes under Cd toxicity. Over to control, the plants grown in Cd alone showed a reduction in the fresh biomass by 48% with more production of oxidative biomarkers (H2O2, SOR, and MDA content) and antioxidative enzymes (SOD, POD, APX, and GR). Further, with the exogenous application of H2S, among all the doses the fresh biomass was found to be maximally increased at 100 µM dose by 76%, and the Cd content was reduced significantly by 25% in the shoot compared to plants grown in Cd treated soil alone. With the decrease in Cd content in the shoot, the production of H2O2, SOR, and MDA content was reduced by 52%, 40%, and 38% respectively, at 100 µM compared to the plants grown in Cd-treated soil. The activities of estimated antioxidative enzymes showed a reduction in their activities up to 100 µM. Whereas, Glutathione reductase (GR) and Phytochelatins (PCs) showed different trends with their higher values in plants treated with NaHS in the presence of Cd. At 100 µM the GR and PCs, respectively showed 48% and 37% increment over Cd-treated plants alone. At this dose, the relative expression of SOD, POD, APX, GR, and PCS5 (Phytochelatin synthetase enzyme) genes, and other functional activities (SEM and fluorescence kinetics) supported the best performance of plants at 100 µM. Therefore, among all the doses, 100 µM dose of H2S has significantly reduced the Cd toxicity by maintaining the growth and other functional traits of plants. The correlation analysis also supported the result by showing a relationship between H2S application and Cd uptake. So, with this strategy, the plants grown in metal-contaminated fields can be improved qualitatively as well as quantitatively. With further experimentation, the mode of application could be explored to increase its efficiency and to promote this strategy at a wider scale. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01389-3.

Auricular reconstruction via 3D bioprinting strategies: An update.

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Novel efficacious microRNA-30c analogs reduce apolipoprotein B secretion in human hepatoma and primary hepatocyte cells.

High plasma lipid levels have been demonstrated to increase cardiovascular disease risk. Despite advances in treatments to decrease plasma lipids, additional therapeutics are still needed because many people are intolerant or nonresponsive to these therapies. We previously showed that increasing cellular levels of microRNA-30c (miR-30c) using viral vectors or liposomes reduces plasma lipids and atherosclerosis. In this study, we aimed to synthesize potent miR-30c analogs that can be delivered to hepatoma cells without the aid of viral vectors and lipid emulsions. We hypothesized that modification of the passenger strand of miR-30c would increase the stability of miR-30c and augment its delivery to liver cells. Here, we report the successful synthesis of a series of miR-30c analogs by using different chemically modified nucleosides. In these analogs, we left the active sense strand untouched so that its biological activity remained unaltered, and we modified the passenger strand of miR-30c to enhance the stability and uptake of miR-30c by hepatoma cells through phosphorothiorate linkages and the addition of GalNAc. We show that these analogs significantly reduced apolipoprotein B secretion in Huh-7 human hepatoma cells and human primary hepatocytes without affecting apolipoprotein A1 secretion and cellular lipid levels. Our results provide a proof of concept that the passenger strand of miR-30c can be modified to increase its stability and delivery to cells while retaining the potency of the sense strand. We anticipate these miR-30c analogs will be useful in the development of more efficacious analogs for the treatment of hyperlipidemias and cardiovascular diseases.

In silico study on spice-derived antiviral phytochemicals against SARS-CoV-2 TMPRSS2 target.

Corona Virus Disease (COVID-19) caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a pandemic that has claimed so far over half a million human life across the globe. Researchers all over the world are exploring various molecules including phytochemicals to get a potential anti-COVID-19 drug. Certain phytochemicals present in some spices are claimed to possess antiviral, anti-bacterial, and anti-fungal properties. Hence, an in-silico study was done by selecting eighteen well reported antiviral phytochemicals from some spices commonly used in Indian kitchen viz. Curcuma longa (Turmeric), Nigella sativa (Black cumin), Piper nigrum (Black pepper), Trachyspermum ammi (Carom) and Zingiber officinale (Ginger) to find out whether they can prevent SARS-CoV-2 infection. Firstly, we predicted the structure of TMPRSS2 (transmembrane protease serine 2), a host protein that truncates spike protein of SARS-CoV-2 thereby facilitating its endocytosis, and then docked against its catalytic domain the selected phytochemicals and camostat (a well-known synthetic inhibitor of TMPRSS2). Thereafter, stability of seven best docked phytochemicals and camostat were scrutinized by Molecular Dynamic Simulation (MDS). MDS analysis indicated bisdemethoxycurcumin (BDMC), carvacrol and thymol as better inhibitors than the camostat due to their stable binding with TMPRSS2 in its oxyanion hole and inducing subtle modification in the spatial arrangement of the catalytic triad residues. Among these three phytochemicals, carvacrol appeared to be the best inhibitor, followed by BDMC, whereas thymol was least effective.

Synthesis of Novel MicroRNA-30c Analogs to Reduce Apolipoprotein B Secretion in Human Hepatoma Cells.

Atherosclerosis, a condition characterized by thickening of the arteries due to lipid deposition, is the major contributor to and hallmark of cardiovascular disease. Although great progress has been made in lowering the lipid plaques in patients, the conventional therapies fail to address the needs of those that are intolerant or non-responsive to the treatment. Therefore, additional novel therapeutic approaches are warranted. We have previously shown that increasing the cellular amounts of microRNA-30c (miR-30c) with the aid of viral vectors or liposomes can successfully reduce plasma cholesterol and atherosclerosis in mice. To avoid the use of viruses and liposomes, we have developed new methods to synthesize novel miR-30c analogs with increasing potency and efficacy, including 2'-O-methyl (2'OMe), 2'-fluoro (2'F), pseudouridine (á´ª), phosphorothioate (PS), and N-acetylgalactosamine (GalNAc). The discovery of these modifications has profoundly impacted the modern RNA therapeutics, as evidenced by their increased nuclease stability and reduction in immune responses. We show that modifications on the passenger strand of miR-30c not only stabilize the duplex but also aid in a more readily uptake by the cells without the aid of viral vectors or lipid emulsions. After uptake, the analogs with PS linkages and GalNAc-modified ribonucleotides significantly reduce the secretion of apolipoprotein B (ApoB) without affecting apolipoprotein A1 (ApoA1) in human hepatoma Huh-7 cells. We envision an enormous potential for these modified miR-30c analogs in therapeutic intervention for treating cardiovascular diseases. This protocol was validated in: J Biol Chem (2021), DOI: 10.1016/j.jbc.2022.101813.

Nitrogen/sulfur-co-doped carbon quantum dots: a biocompatible material for the selective detection of picric acid in aqueous solution and living cells.

Here, a fast and eco-friendly one-pot hydrothermal technique is utilized for the synthesis of nitrogen/sulfur-co-doped fluorescent carbon quantum dots (NS-CQDs) from a simple precursor of citric acid (CA) and thiosemicarbazide (TSC). The obtained NS-CQDs exhibited strong blue emission under UV light, with fluorescence quantum yield (QY) of ~37.8%. The Commission internationale de l'eclairage (CIE) coordinates originated at (0.15, 0.07), which confirmed the blue fluorescence of the synthesized NS-CQDs. Interestingly, the prepared NS-CQDs were successfully used as a selective nanoprobe for the monitoring of environmentally hazardous explosive picric acid (PA) in different nitro- and non-nitro-aromatic derivatives of PA. The mechanism of the NS-CQDs was also explored, and was posited to occur via the fluorescence resonance electron transfer (FRET) process and non-fluorescent complex formation. Importantly, this system possesses excellent biocompatibility and low cytotoxicity in HeLa cervical cancer cells; hence, it can potentially be used for PA detection in analytical, environmental, and pathological applications. Furthermore, the practical applicability of the proposed sensing system to pond water demonstrated the feasibility of our system along with good recovery. Graphical abstract.

Highly fluorescent carbon dots from wheat bran as a novel drug delivery system for bacterial inhibition.

In this study, we prepared carbon dots (CDs) from wheat bran via hydrothermal treatment at 180°C for 3 h. The prepared CDs showed blue-green fluorescence under UV light. The fluorescence emission study of the CDs revealed that they showed maximum fluorescence emission at 500 nm. The prepared CDs showed a high quantum yield of 33.23%. Solvent-dependent fluorescence emission analysis of the CDs was performed to study the variation in fluorescence emission characteristics with solvent polarity. The prepared CDs were conjugated with amoxicillin (AMX) to explore its potential for use as a drug delivery agent for AMX. The drug release profile of the CD-AMX conjugates was analyzed at different pH (5.0, 6.8 and 7.2) to study drug release kinetics. CD-AMX conjugates showed notable bacterial inhibition against Gram-positive (S. aureus) and Gram-negative (E. coli) strains with minimal cytotoxic effects, indicating its potential as a promising antibacterial drug delivery system.

Mustard seeds derived fluorescent carbon quantum dots and their peroxidase-like activity for colorimetric detection of H2O2 and ascorbic acid in a real sample.

Herein, we were synthesized fluorescent carbon quantum dots via facile one-step hydrothermal treatment of mustard seeds (M-CQDs). It showed excellent optical property with fluorescent quantum yield 4.6%. The as-prepared M-CQDs exhibited peroxidase-like mimetic activity and catalyzed the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue color reaction mixture with the prominent peak at 652 nm. Furthermore, the peroxidase-like catalytic performance of M-CQDs followed the steady-state kinetics behavior and exhibited similar catalytic activity as that of natural enzyme Horseradish peroxidase (HRP). In addition to this, the double reciprocal plot showed a parallel line which suggested the occurrence of Ping-Pong type of mechanism. The H2O2 dependent oxidation of TMB was helpful for the colorimetric detection of H2O2 in the linear range of 0.02-0.20 mM with the limit of detection (LOD) of 0.015 mM. Interestingly, the oxidized TMB (ox-TMB) was further reduced to native TMB by the reducing agent ascorbic acid. Hence M-CQDs showed its potential towards the selective and sensitive detection of ascorbic acid in the linear range of 10-70 µM having a correlation coefficient of 0.998 with LOD of 3.26 µM. The practical feasibility of the proposed detection method of AA was also investigated in common fresh fruits.

Green Synthesis of Fluorescent Carbon Quantum Dots from Azadirachta indica Leaves and Their Peroxidase-Mimetic Activity for the Detection of H2O2 and Ascorbic Acid in Common Fresh Fruits.

In the present study, an ecofriendly and zero-cost approach has been demonstrated for the preparation of carbon quantum dots by one-pot hydrothermal treatment of leaf extracts of neem (Azadirachta indica). The as-synthesized neem carbon quantum dots (N-CQDs) exhibited high fluorescent quantum yields (QYs) up to 27.2%. Moreover, N-CQDs also act with a peroxidase-like-mimetic activity toward the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in association with hydrogen peroxide (H2O2). Further, the kinetics of peroxidase-like catalytic activity follows the Michaelis-Menten and ping-pong pathway. In addition, the H2O2 sensitive TMB oxidation motivated the colorimetric detection of H2O2 which showed linearity from 0.1 to 0.5 mmol/L with a detection limit (LOD) of 0.035 mmol/L. Furthermore, the blue colors of oxidized TMB (ox-TMB) were selectively reduced in native TMB with ascorbic acid (AA) without any interference of other reducing agents. The linear range of AA detection was lying between 5 and 40 µM with a LOD up to 1.773 µM. The practicability assay of the proposed sensing system toward the detection of AA was also investigated in real sample analysis such as common fruits which showed good sensitivity to the presence of AA. Therefore, this convenient, ecofriendly, and cost-effective peroxidase-based sensing system opens a new platform for analysis of AA in real samples and in complex biological systems.

Peroxidase mimetic activity of fluorescent NS-carbon quantum dots and their application in colorimetric detection of H2O2 and glutathione in human blood serum.

Interest is growing in the development of artificial enzymes to overcome the drawbacks of natural enzymes. Herein, we have synthesized nitrogen-sulphur dual-doped carbon quantum dots (NS-CQDs) via a one-step hydrothermal method; the NS-CQDs possess excellent optical properties and a high fluorescent quantum yield (46%). Significantly, the NS-CQDs exhibited peroxidase mimetic enzyme activity without support from metals or polymeric materials and efficiently catalyzed the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue solution with an absorption maximum at 652 nm. Mechanistic studies suggest that the small size and high electron density of NS-CQDs play vital roles and accelerate the reduction of H2O2 to generate ˙OH radical, which facilitates the oxidation of TMB. The catalytic activity is based on Michaelis-Menten kinetic behavior, and steady state kinetic analysis suggests that the NS-CQDs exhibit a higher affinity for H2O2 than TMB, similar to the natural enzyme horseradish peroxidase (HRP). Moreover, the catalytic pathway follows a ping-pong mechanism. Therefore, these findings offer a worthy platform for colorimetric detection of H2O2 in a linear range of 0.02 mM to 0.1 mM with a limit of detection of 0.004 mM. Interestingly, the blue colour of oxidized TMB showed excellent selectivity over non-thiolate biological molecules, especially amino acids, and glutathione can be detected up to 0.07 µM via colorimetric and fluorimetric assays. Additionally, this system showed excellent recovery (96.0-108.3%) of GSH from human blood serum. Thus, the proposed sensing system is simple, convenient, and straightforward and can be potentially applied for real time monitoring of H2O2 and glutathione in biological samples.

The m6A methyltransferase Ime4 and mitochondrial functions in yeast.

In eukaryotes, the precise transcriptional and post-transcriptional regulations of gene expression are crucial for the developmental processes. More than 100 types of post-transcriptional RNA modifications have been identified in eukaryotes. The deposition of N6-methyladenosine (m6A) into mRNA is among the most common post-transcriptional RNA modifications known in eukaryotes. It has been reported that m6A RNA modification can regulate gene expression. The role of yeast m6A methyltransferase (Ime4) in meiosis and sporulation in diploid cells is very well proven, but its physiological role in haploid cells has remained unknown until recently. Previously, we have shown that Ime4 epitranscriptionally regulates triacylglycerol (TAG) metabolism and vacuolar morphology in haploid cells. Mitochondrial dysfunction leads to TAG accumulation as lipid droplets (LDs) in the cells; besides, LDs are physically connected to the mitochondria. As of now there are no reports on the role of Ime4 in mitochondrial biology. Here we report the important role played by Ime4 in the mitochondrial morphology and functions in Saccharomyces cerevisiae. The confocal microscopic analysis showed that IME4 gene deletion causes mitochondrial fragmentation; besides, the ime4Δ cells showed a significant decrease in cytochrome c oxidase and citrate synthase activities compared to the wild-type cells. IME4 gene deletion causes mitochondrial dysfunction, and it will be interesting to find out the target genes of Ime4 related to the mitochondrial biology. The determination of the role of Ime4 and its targets in mitochondrial biology could probably help in formulating potential cures for the mitochondria-linked rare genetic disorders.

The role of yeast m6A methyltransferase in peroxisomal fatty acid oxidation.

The precise and controlled regulation of gene expression at transcriptional and post-transcriptional levels is crucial for the eukaryotic cell survival and functions. In eukaryotes, more than 100 types of post-transcriptional RNA modifications have been identified. The N6-methyladenosine (m6A) modification in mRNA is among the most common post-transcriptional RNA modifications known in eukaryotic organisms, and the m6A RNA modification can regulate gene expression. The role of yeast m6A methyltransferase (Ime4) in meiosis, sporulation, triacylglycerol metabolism, vacuolar morphology, and mitochondrial functions has been reported. Stress triggers triacylglycerol accumulation as lipid droplets. Lipid droplets are physically connected to the different organelles such as endoplasmic reticulum, mitochondria, and peroxisomes. However, the physiological relevance of these physical interactions remains poorly understood. In yeast, peroxisome is the sole site of fatty acid ß-oxidation. The metabolic status of the cell readily governs the number and physiological function of peroxisomes. Under low-glucose or stationary-phase conditions, peroxisome biogenesis and proliferation increase in the cells. Therefore, we hypothesized a possible role of Ime4 in the peroxisomal functions. There is no report on the role of Ime4 in peroxisomal biology. Here, we report that IME4 gene deletion causes peroxisomal dysfunction under stationary-phase conditions in Saccharomyces cerevisiae; besides, the ime4Δ cells showed a significant decrease in the expression of the key genes involved in peroxisomal ß-oxidation compared to the wild-type cells. Therefore, identification and determination of the target genes of Ime4 that are directly involved in the peroxisomal biogenesis, morphology, and functions will pave the way to better understand the role of m6A methylation in peroxisomal biology.

The m6A methyltransferase Ime4 epitranscriptionally regulates triacylglycerol metabolism and vacuolar morphology in haploid yeast cells.

N6-Methyladenosine (m6A) is among the most common modifications in eukaryotic mRNA. The role of yeast m6A methyltransferase, Ime4, in meiosis and sporulation in diploid strains is very well studied, but its role in haploid strains has remained unknown. Here, with the help of an immunoblotting strategy and Ime4-GFP protein localization studies, we establish the physiological role of Ime4 in haploid cells. Our data showed that Ime4 epitranscriptionally regulates triacylglycerol metabolism and vacuolar morphology through the long-chain fatty acyl-CoA synthetase Faa1, independently of the RNA methylation complex (MIS complex). The MIS complex consists of the Ime4, Mum2, and Slz1 proteins. Our affinity enrichment strategy (methylated RNA immunoprecipitation assays) using m6A polyclonal antibodies coupled with mRNA isolation, quantitative real-time PCR, and standard PCR analyses confirmed the presence of m6A-modified FAA1 transcripts in haploid yeast cells. The term "epitranscriptional regulation" encompasses the RNA modification-mediated regulation of genes. Moreover, we demonstrate that the Aft2 transcription factor up-regulates FAA1 expression. Because the m6A methylation machinery is fundamentally conserved throughout eukaryotes, our findings will help advance the rapidly emerging field of RNA epitranscriptomics. The metabolic link identified here between m6A methylation and triacylglycerol metabolism via the Ime4 protein provides new insights into lipid metabolism and the pathophysiology of lipid-related metabolic disorders, such as obesity. Because the yeast vacuole is an analogue of the mammalian lysosome, our findings pave the way to better understand the role of m6A methylation in lysosome-related functions and diseases.

Cardiolipin deficiency causes triacylglycerol accumulation in Saccharomyces cerevisiae.

In yeast, the synthesis of cardiolipin (CL) and phosphatidylethanolamine (PE) occurs mainly in mitochondria. CL and PE have overlapping functions, and they are required for mitochondrial function. PE is physiologically linked with triacylglycerol (TAG) metabolism in Saccharomyces cerevisiae, involving an acyl-CoA-independent pathway through the phospholipid:diacylglycerol acyltransferase activity of the Lro1 protein. There is no report on the physiological link between CL and TAG metabolism. Here we report a metabolic link between CL and TAG accumulation in the S. cerevisiae. Our data indicated that CL deficiency causes TAG accumulation, involving an acyl-CoA-dependent pathway through the diacylglycerol acyltransferase activity of the Dga1 protein with no changes in the TAG molecular species. The DGA1 gene deletion from the CL-deficient strains reduced the TAG levels. Data from in vitro and in vivo analyses showed that CL did not affect the enzymatic activity of Dga1. Our data also showed that CL deficiency leads to the up-regulation of acetyl-CoA synthetase genes (ACS1 and ACS2) of the cytosolic pyruvate dehydrogenase bypass pathway. This study establishes a physiological link between CL and TAG metabolism in S. cerevisiae.

Misregulation of a DDHD Domain-containing Lipase Causes Mitochondrial Dysfunction in Yeast.

The DDHD domain-containing proteins, which belong to the intracellular phospholipase A1 (iPLA1) family, have been predicted to be involved in phospholipid metabolism, lipid trafficking, membrane turnover, and signaling. Defective cardiolipin (CL), phosphatidylethanolamine, and phosphatidylglycerol remodeling cause Barth syndrome and mitochondrial dysfunction. Here, we report that Yor022c is a Ddl1 (DDHD domain-containing lipase 1) that hydrolyzes CL, phosphatidylethanolamine, and phosphatidylglycerol. Ddl1 has been implicated in the remodeling of mitochondrial phospholipids and CL degradation. Our data also suggested that the accumulation of monolysocardiolipin is deleterious to the cells. We show that Aft1 and Aft2 transcription factors antagonistically regulate the DDL1 gene. This study reveals that the misregulation of DDL1 by Aft1/2 transcription factors alters CL metabolism and causes mitochondrial dysfunction in the cells. In humans, mutations in the DDHD1 and DDHD2 genes cause specific types of hereditary spastic paraplegia (SPG28 and SPG54, respectively), and the yeast DDL1-defective strain produces similar phenotypes of hereditary spastic paraplegia (mitochondrial dysfunction and defects in lipid metabolism). Therefore, the DDL1-defective strain could be a good model system for understanding hereditary spastic paraplegia.