Strategies to Study Desmin in Cardiac Muscle and Culture Systems

Crusting-fabricated three-dimensional soy-based scaffolds for cultured meat production: A preliminary study

Crusting has been developed as a non-chemical and non-machine intensive scaffold fabrication method. This method is based on the self-assembling ability of soy biomolecules, allowing the fabrication of a three-dimensional network for cell growth. Preliminary characterization revealed differences in pore size, water absorption, and degradation between pure soy-based scaffold (Y2R) and with added glycerol (Y2G). The Fourier-transform infrared spectrum absorbance peaks of functional groups related to proteins, carbohydrates, and lipids hinted the integration of soy biomolecules potentially via the Maillard reaction, as supported by the visible browning of the scaffold surface. Microscopic images revealed aligned myotubes in both scaffolds, with Y2G myotubes having greater proximity after 72 h of proliferation. Both spontaneous and electro-stimulated contractions were recorded as early as 72 h in proliferation medium. Crusting-fabricated soy-based scaffolds can further be explored for its application in cultured meat production.

Validation of positional candidates Rps6ka6 and Pou3f4 for a locus associated with skeletal muscle mass variability

Genetic variability significantly contributes to individual differences in skeletal muscle mass; however, the specific genes involved in that process remain elusive. In this study, we examined the role of positional candidates, Rps6ka6 and Pou3f4, of a chromosome X locus, implicated in muscle mass variability in CFW laboratory mice. Histology of hindlimb muscles was studied in CFW male mice carrying the muscle "increasing" allele C (n = 15) or "decreasing" allele T (n = 15) at the peak marker of the locus, rs31308852, and in the Pou3f4y/- and their wild-type male littermates. To study the role of the Rps6ka6 gene, we deleted exon 7 (Rps6ka6-ΔE7) using clustered regularly interspaced palindromic repeats-Cas9 based method in H2Kb myogenic cells creating a severely truncated RSK4 protein. We then tested whether that mutation affected myoblast proliferation, migration, and/or differentiation. The extensor digitorum longus muscle was 7% larger (P < 0.0001) due to 10% more muscle fibers (P = 0.0176) in the carriers of the "increasing" compared with the "decreasing" CFW allele. The number of fibers was reduced by 15% (P = 0.0268) in the slow-twitch soleus but not in the fast-twitch extensor digitorum longus (P = 0.2947) of Pou3f4y/- mice. The proliferation and migration did not differ between the Rps6ka6-ΔE7 and wild-type H2Kb myoblasts. However, indices of differentiation (myosin expression, P < 0.0001; size of myosin-expressing cells, P < 0.0001; and fusion index, P = 0.0013) were significantly reduced in Rps6ka6-ΔE7 cells. This study suggests that the effect of the X chromosome locus on muscle fiber numbers in the fast-twitch extensor digitorum longus is mediated by the Rps6ka6 gene, whereas the Pou3f4 gene affects fiber number in slow-twitch soleus.

Unraveling Desmin's Head Domain Structure and Function

Understanding the structure and function of intermediate filaments (IFs) is necessary in order to explain why more than 70 related IF genes have evolved in vertebrates while maintaining such dramatically tissue-specific expression. Desmin is a member of the large multigene family of IF proteins and is specifically expressed in myocytes. In an effort to elucidate its muscle-specific behavior, we have used a yeast two-hybrid system in order to identify desmin's head binding partners. We described a mitochondrial and a lysosomal protein, NADH ubiquinone oxidoreductase core subunit S2 (NDUFS2), and saposin D, respectively, as direct desmin binding partners. In silico analysis indicated that both interactions at the atomic level occur in a very similar way, by the formation of a three-helix bundle with hydrophobic interactions in the interdomain space and hydrogen bonds at R16 and S32 of the desmin head domain. The interactions, confirmed also by GST pull-down assays, indicating the necessity of the desmin head domain and, furthermore, point out its role in function of mitochondria and lysosomes, organelles which are disrupted in myopathies due to desmin head domain mutations.

Methionine availability influences essential H3K36me3 dynamics during cell differentiation

Histone modifications are integral to epigenetics through their influence on gene expression and cellular status. While it's established that metabolism, including methionine metabolism, can impact histone methylation, the direct influence of methionine availability on crucial histone marks that determine the epigenomic process remains poorly understood. In this study, we demonstrate that methionine, through its metabolic product, S-adenosylmethionine (SAM), dynamically regulates H3K36me3, a cancer-associated histone modification known to influence cellular status, and myogenic differentiation of mouse myoblast cells. We further demonstrate that the methionine-dependent effects on differentiation are mediated in part through the histone methyltransferase SETD2. Methionine restriction leads to preferential decreases in H3K36me3 abundance and genome accessibility of genes involved in myogenic differentiation. Importantly, the effects of methionine restriction on differentiation and chromatin accessibility can be phenocopied by the deletion of Setd2. Collectively, this study demonstrates that methionine metabolism through its ability to be sensed by chromatin modifying enzymes can have a direct role in influencing cell fate determination.

Advanced Drug Delivery Modulation via Hybrid Nanofibers Enhances Stem Cell Differentiation

Seamlessly integrating soluble factors onto biomedical scaffolds with a precisely manufactured topography for efficient cell control remains elusive since many scaffold fabrication techniques degrade payloads. Surface adsorption of payloads onto synthesized nanoscaffolds retains bioactivity by removing exposure to harsh processing conditions at the expense of inefficient drug loading and uncontrolled release. Herein, we present a nanomaterial composite scaffold paradigm to improve physicochemical surface adsorption pharmacokinetics. As a proof of concept, we integrated graphene oxide (GO) and manganese dioxide (MnO2) nanosheets onto nanofibers to increase loading capacity and tune drug release. Non-degradable GO enhances payload retention, while biodegradable MnO2 enables cell-responsive drug release. To demonstrate the utility of this hybrid nanomaterial scaffold paradigm for tissue engineering, we adsorbed payloads ranging from small molecules to proteins onto the scaffold to induce myogenesis and osteogenesis for multiple stem cell lines. Scaffolds with adsorbed payloads enabled more efficient differentiation than media supplementation using equivalent quantities of differentiation factors. We attribute this increased efficacy to a reverse uptake mechanism whereby payloads are localized around seeded cells, increasing delivery efficiency for guiding differentiation. Additionally, we demonstrate spatial control over cells since differentiation factors are delivered locally through the scaffold. When co-culturing scaffolds with and without adsorbed payloads, only cells seeded on payload-adsorbed scaffolds underwent differentiation. With this modular technology being capable of enhancing multiple differentiation fates for specific cell lines, this technology provides a promising alternative for current tissue engineering scaffolds.

Myospryn deficiency leads to impaired cardiac structure and function and schizophrenia-associated symptoms

The desmin-associated protein myospryn, encoded by the cardiomyopathy-associated gene 5 (CMYA5), is a TRIM-like protein associated to the BLOC-1 (Biogenesis of Lysosomes Related Organelles Complex 1) protein dysbindin. Human myospryn mutations are linked to both cardiomyopathy and schizophrenia; however, there is no evidence of a direct causative link of myospryn to these diseases. Therefore, we sought to unveil the role of myospryn in heart and brain. We have genetically inactivated the myospryn gene by homologous recombination and demonstrated that myospryn null hearts have dilated phenotype and compromised cardiac function. Ultrastructural analyses revealed that the sarcomere organization is not obviously affected; however, intercalated disk (ID) integrity is impaired, along with mislocalization of ID and sarcoplasmic reticulum (SR) protein components. Importantly, cardiac and skeletal muscles of myospryn null mice have severe mitochondrial defects with abnormal internal vacuoles and extensive cristolysis. In addition, swollen SR and T-tubules often accompany the mitochondrial defects, strongly implying a potential link of myospryn together with desmin to SR- mitochondrial physical and functional cross-talk. Furthermore, given the reported link of human myospryn mutations to schizophrenia, we performed behavioral studies, which demonstrated that myospryn-deficient male mice display disrupted startle reactivity and prepulse inhibition, asocial behavior, decreased exploratory behavior, and anhedonia. Brain neurochemical and ultrastructural analyses revealed prefrontal-striatal monoaminergic neurotransmitter defects and ultrastructural degenerative aberrations in cerebellar cytoarchitecture, respectively, in myospryn-deficient mice. In conclusion, myospryn is essential for both cardiac and brain structure and function and its deficiency leads to cardiomyopathy and schizophrenia-associated symptoms.

Muscular G9a Regulates Muscle-Liver-Fat Axis by Musclin Under Overnutrition in Female Mice

Cross talk among different tissues and organs is a hotspot in metabolic research. Recent studies have revealed the regulatory roles of a number of myokines in metabolism. Here, we report that female mice lacking muscle-specific histone methylase G9a (Ehmt2 ^Ckmm knockout [KO] or Ehmt2 ^HSA KO) are resistant to high-fat diet (HFD)-induced obesity and hepatic steatosis. Furthermore, we identified a significantly upregulated circulating level of musclin, a myokine, in HFD-fed Ehmt2 ^Ckmm KO or Ehmt2 ^HSA KO female mice. Similarly, upregulated musclin was observed in mice injected with two structurally different inhibitors for G9a methylase activity: BIX01294 and A366. Moreover, injection of recombinant full-length musclin or its functional core domain inhibited the HFD-induced obesity and hepatic steatosis in wild-type female and male mice. Mechanistically, G9a methylase activity-dependently regulated muscular musclin level by binding to its promoter, also by regulating phosphorylated-FOXO1/FOXO1 levels in vivo and in vitro. Collectively, these data suggest a critical role for G9a in the muscle-liver-fat metabolic axis, at least for female mice. Musclin may serve as a potential therapeutic candidate for obesity and associated diseases.

Implications of the mitochondrial interactome of mammalian thioredoxin 2 for normal cellular function and disease

Multiple thioredoxin isoforms exist in all living cells. To explore the possible functions of mammalian mitochondrial thioredoxin 2 (Trx2), an interactome of mouse Trx2 was initially created using (i) a monothiol mouse Trx2 species for capturing protein partners from different organs and (ii) yeast two hybrid screens on human liver and rat brain cDNA libraries. The resulting interactome consisted of 195 proteins (Trx2 included) plus the mitochondrial 16S RNA. 48 of these proteins were classified as mitochondrial (MitoCarta2.0 human inventory). In a second step, the mouse interactome was combined with the current four-membered mitochondrial sub-network of human Trx2 (BioGRID) to give a 53-membered human Trx2 mitochondrial interactome (52 interactor proteins plus the mitochondrial 16S RNA). Although thioredoxins are thiol-employing disulfide oxidoreductases, approximately half of the detected interactions were not due to covalent disulfide bonds. This finding reinstates the extended role of thioredoxins as moderators of protein function by specific non-covalent, protein-protein interactions. Analysis of the mitochondrial interactome suggested that human Trx2 was involved potentially in mitochondrial integrity, formation of iron sulfur clusters, detoxification of aldehydes, mitoribosome assembly and protein synthesis, protein folding, ADP ribosylation, amino acid and lipid metabolism, glycolysis, the TCA cycle and the electron transport chain. The oxidoreductase functions of Trx2 were verified by its detected interactions with mitochondrial peroxiredoxins and methionine sulfoxide reductase. Parkinson's disease, triosephosphate isomerase deficiency, combined oxidative phosphorylation deficiency, and lactate dehydrogenase b deficiency are some of the diseases where the proposed mitochondrial network of Trx2 may be implicated.

Amelioration of desmin network defects by αB-crystallin overexpression confers cardioprotection in a mouse model of dilated cardiomyopathy caused by LMNA gene mutation

The link between the cytoplasmic desmin intermediate filaments and those of nuclear lamins serves as a major integrator point for the intracellular communication between the nucleus and the cytoplasm in cardiac muscle. We investigated the involvement of desmin in the cardiomyopathy caused by the lamin A/C gene mutation using the Lmna^H222P/H222P mouse model of the disease. We demonstrate that in these mouse hearts desmin loses its normal Z disk and intercalated disc localization and presents aggregate formation along with mislocalization of basic intercalated disc protein components, as well as severe structural abnormalities of the intercalated discs and mitochondria. To address the extent by which the observed desmin network defects contribute to the progression of Lmna^H222P/H222P cardiomyopathy, we investigated the consequences of desmin-targeted approaches for the disease treatment. We showed that cardiac-specific overexpression of the small heat shock protein αΒ-Crystallin confers cardioprotection in Lmna^H222P/H222P mice by ameliorating desmin network defects and by attenuating the desmin-dependent mislocalization of basic intercalated disc protein components. In addition, αΒ-Crystallin overexpression rescues the intercalated disc, mitochondrial and nuclear defects of Lmna^H222P/H222P hearts, as well as the abnormal activation of ERK1/2. Consistent with that, by generating the Lmna^H222P/H222PDes+/- mice, we showed that the genetically decreased endogenous desmin levels have cardioprotective effects in Lmna^H222P/H222P hearts since less desmin is available to form dysfunctional aggregates. In conclusion, our results demonstrate that desmin network disruption, disorganization of intercalated discs and mitochondrial defects are a major mechanism contributing to the progression of this LMNA cardiomyopathy and can be ameliorated by αΒ-Crystallin overexpression.

Intermediate filaments in cardiomyopathy

Intermediate filament (IF) proteins are critical regulators in health and disease. The discovery of hundreds of mutations in IF genes and posttranslational modifications has been linked to a plethora of human diseases, including, among others, cardiomyopathies, muscular dystrophies, progeria, blistering diseases of the epidermis, and neurodegenerative diseases. The major IF proteins that have been linked to cardiomyopathies and heart failure are the muscle-specific cytoskeletal IF protein desmin and the nuclear IF protein lamin, as a subgroup of the known desminopathies and laminopathies, respectively. The studies so far, both with healthy and diseased heart, have demonstrated the importance of these IF protein networks in intracellular and intercellular integration of structure and function, mechanotransduction and gene activation, cardiomyocyte differentiation and survival, mitochondrial homeostasis, and regulation of metabolism. The high coordination of all these processes is obviously of great importance for the maintenance of proper, life-lasting, and continuous contraction of this highly organized cardiac striated muscle and consequently a healthy heart. In this review, we will cover most known information on the role of IFs in the above processes and how their deficiency or disruption leads to cardiomyopathy and heart failure.

Opposite effects of catalase and MnSOD ectopic expression on stress induced defects and mortality in the desmin deficient cardiomyopathy model

Oxidative stress has been linked strongly to cell death and cardiac remodeling processes, all hallmarks of heart failure. Mice deficient for desmin (des-/-), the major muscle specific intermediate filament protein, develop dilated cardiomyopathy and heart failure characterized by mitochondrial defects and cardiomyocyte death. The cellular and biochemical alterations in the hearts of these mice strongly suggest that oxidative stress is one of the mechanisms contributing to the pathogenesis of the phenotype. Recently, we showed that indeed the desmin deficient cardiomyocytes are under increased oxidative stress. In order to verify these findings in vivo, we generated transgenic animals overexpressing SOD2 (MnSOD) and/or catalase in the heart and crossed them with des-/- mice, thus allowing us to evaluate the contribution of oxidative injury in inherited cardiomyopathies, as well as the therapeutic potential of antioxidant strategies. Moderate MnSOD and/or catalase overexpression in des-/- hearts leads to a marked decrease in intracellular reactive oxygen species (ROS), ameliorates mitochondrial and other ultrastructural defects, minimizes myocardial degeneration and leads to a significant improvement of cardiac function. Importantly, catalase overexpression increased the 50% survival rate of des-/- mice in an obligatory exercise to 100%. In contrast, MnSOD overexpression enhanced the lethality of des-/- mice, underscoring the importance of a fine balanced cellular redox status. Overall, the present study supports the contribution of oxidative stress in the development of des-/- cardiomyopathy and points to a well-considered antioxidant treatment as therapeutic for cardiomyopathies.

Desmin and αB-crystallin interplay in the maintenance of mitochondrial homeostasis and cardiomyocyte survival

The association of desmin with the α-crystallin Β-chain (αΒ-crystallin; encoded by CRYAB), and the fact that mutations in either one of them leads to heart failure in humans and mice, suggests a potential compensatory interplay between the two in cardioprotection. To address this hypothesis, we investigated the consequences of αΒ-crystallin overexpression in the desmin-deficient (Des^-/-) mouse model, which possesses a combination of the pathologies found in most cardiomyopathies, with mitochondrial defects as a hallmark. We demonstrated that cardiac-specific αΒ-crystallin overexpression ameliorates all these defects and improves cardiac function to almost wild-type levels. Protection by αΒ-crystallin overexpression is linked to maintenance of proper mitochondrial protein levels, inhibition of abnormal mitochondrial permeability transition pore activation and maintenance of mitochondrial membrane potential (Δψ_m). Furthermore, we found that both desmin and αΒ-crystallin are localized at sarcoplasmic reticulum (SR)-mitochondria-associated membranes (MAMs), where they interact with VDAC, Mic60 - the core component of mitochondrial contact site and cristae organizing system (MICOS) complex - and ATP synthase, suggesting that these associations could be crucial in mitoprotection at different levels.