Biology subjects

Tapia, O.

Publications and source records attributed to Tapia, O..

4 recordsLinked to original sources

bioRxiv2024

SMN deficiency induces an early non-atrophic myopathy with alterations in the contractile and excitatory coupling machinery of skeletal myofibers in the SMN{triangleup}7 mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by a deficiency of the ubiquitously expressed survival motor neuron (SMN) protein. The main pathological hallmark of SMA is the degeneration of lower motor neurons (MNs) with subsequent denervation and atrophy of skeletal muscle. However, increasing evidence indicates that low SMN levels not only are detrimental to the central nervous system but also directly affect other peripheral tissues and organs, including skeletal muscle. To better understand the potential primary impact of SMN deficiency in muscle, we explored the cellular, ultrastructural, and molecular basis of SMA myopathy in the SMN{Delta}7 mouse model of severe SMA at an early postnatal period (P0-7) prior to muscle denervation and MN loss (preneurodegenerative [PND] stage). This period contrasts with the neurodegenerative (ND) stage (P8-14), in which MN loss and muscle atrophy occur. At the PND stage, we found that SMN{Delta}7 mice displayed early signs of motor dysfunction with overt myofiber alterations in the absence of atrophy. Focal and segmental lesions in the myofibrillar contractile apparatus were noticed in myofibers. These lesions were observed in association with specific myonuclear domains and included abnormal accumulations of actin-thin myofilaments, sarcomere disruption, and the formation of minisarcomeres. The sarcoplasmic reticulum and triads also exhibited ultrastructural alterations, suggesting decoupling during the excitation-contraction process. Finally, changes in intermyofibrillar mitochondrial organization and dynamics, indicative of mitochondrial biogenesis overactivation, were also found. Overall, our results demonstrated that SMN deficiency induces early and MN loss-independent alterations in myofibers that essentially contribute to SMA myopathy. This strongly supports the view of an intrinsic alteration of skeletal muscle in SMA, suggesting that this peripheral tissue is a key therapeutic target for the disease. Graphical summarySchematic representation of the main cellular and ultrastructural changes occurring in tibialis anterior (TA) myofibers of the SMN{Delta}7 mouse model of severe SMA during the pre-neurodegenerative stage (PND, P0-P7). See that the PND stage is characterized by the absence of MN loss and muscular atrophy but, SMN deficient myofibers display multiple alterations. Observe the early impact of low SMN levels on sarcoplasmic reticulum and triads, myofibril contractile cytoskeleton, and intermyofibrillar mitochondria. Notice that all alterations are associated with a specific myonuclear domain. Changes in mRNA levels of different genes involved in myogenesis and mitochondrial biogenesis are also shown compared to age-matched WT animals. Figure created with BioRender.com. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=188 SRC="FIGDIR/small/612470v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@17ae050org.highwire.dtl.DTLVardef@1cd31borg.highwire.dtl.DTLVardef@67c2e9org.highwire.dtl.DTLVardef@2d5141_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Lem2 is essential for cardiac development by maintaining nuclear integrity

Nuclear envelope integrity is essential for compartmentalisation of nucleus and cytoplasm. Importantly, mutations in nuclear envelope-encoding genes are the second-highest cause of familial dilated cardiomyopathy. One such nuclear envelope protein that causes cardiomyopathy in humans and affects mouse heart development is Lem2. However, its role in mechanically active tissue such as heart remains poorly understood. We generated mice in which Lem2 was specifically ablated in cardiomyocytes and carried out detailed physiological, tissue and cellular analyses. Importantly, our data showed that Lem2 was essential for cardiac development, and hearts from Lem2 cKO mice were morphologically and transcriptionally underdeveloped. Lem2 cKO hearts displayed high levels of DNA damage, nuclear rupture, and apoptosis. Crucially, we found that these defects were driven by muscle contraction as they were ameliorated by inhibiting myosin contraction and conversely were exacerbated upon myosin activation. Our data suggest that Lem2 is critical for integrity at the nascent nuclear envelope in fetal hearts, and protects the nucleus from the mechanical forces of muscle contraction. Taken together, these data provide novel insight into mechanisms underlying striated muscle diseases caused by altered nuclear envelope integrity.

cell biology↗

bioRxiv2020

TDP-43 and HSP70 phase separate into anisotropic, intranuclear liquid spherical annuli

The RNA binding protein TDP-43 naturally phase separates within cell nuclei and forms cytoplasmic aggregates in age-related neurodegenerative diseases. Here we show that acetylation-mediated inhibition of TDP-43 binding to RNA produces co-de-mixing of acetylated and unmodified TDP-43 into symmetrical, intranuclear spherical annuli whose shells and cores have liquid properties. Shells are anisotropic, like liquid crystals. Consistent with our modelling predictions that annulus formation is driven by components with strong self-interactions but weak interaction with TDP-43, the major components of annuli cores are identified to be HSP70 family proteins, whose chaperone activity is required to maintain liquidity of the core. Proteasome inhibition, mimicking reduction in proteasome activity during aging, induces TDP-43-containing annuli in neurons in rodents. Thus, we identify that TDP-43 phase separation is regulated by acetylation, proteolysis, and ATPase-dependent chaperone activity of HSP70. One Sentence SummaryAcetylation of TDP-43 drives its phase separation into spherical annuli that form a liquid-inside-a-liquid-inside-a-liquid.

cell biology↗

bioRxiv2018

Identification of new transmembrane proteins concentrated at the nuclear envelope using organellar proteomics of mesenchymal cells

The nuclear envelope (NE) is an endoplasmic reticulum (ER) subdomain that contains characteristic components dedicated to nuclear functions. These include nuclear pore complexes (NPCs) - the channels for nucleocytoplasmic transport, and the nuclear lamina (NL) - a scaffold for NE and chromatin organization at the nuclear periphery. Since numerous human diseases associated with NE/NL proteins occur in mesenchyme-derived cells, a more comprehensive characterization of proteins concentrated at the NE in these cell types is warranted. Accordingly, we used proteomics to analyze NE and other subcellular fractions isolated from mesenchymal stem cells and from differentiated adipocytes and myocytes. We evaluated the proteomics datasets to calculate relative protein enrichment in the NE fraction, using a spectral abundance-based scoring system that accurately described most benchmark proteins. We then examined five high-scoring transmembrane proteins expressed in all three cell types that were not previously known to be enriched at the NE. Using quantitative immunofluorescence microscopy to track ectopically expressed proteins, we validated that all five of these components are substantially concentrated at the NE of multiple cell types. One (Itprip) is exposed to the outer nuclear membrane, a second (Smpd4) is enriched at the NPC, and the three others (Mfsd10, Tmx4, and Arl6ip6) are suggested to reside in the inner nuclear membrane. Considering their sequences and other features, these proteins provide new focal points for studying the functions and membrane dynamics of the NE. Our datasets should be useful for identifying additional NE-concentrated proteins, and for evaluating candidates that are identified in screening.

cell biology↗