Biology subjects

Grandi, F. C.

Publications and source records attributed to Grandi, F. C..

4 recordsLinked to original sources

bioRxiv2025

Genomic stress drives activation of interferon signaling and innate immune pathways during SMA Type II myoblasts differentiation

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by loss of the SMN1 gene. The SMN protein is ubiquitously expressed and has several roles in the cell, including the regulation of RNA metabolism and genome stability. Although SMA is primarily considered a motor neuron disease, because of its ubiquitous expression, loss of SMN leads to systemic pathological consequences, including in skeletal muscle. To better understand the cell-intrinsic effects of SMN loss on myoblast differentiation, we characterized three human SMA Type II myoblast cell lines and controls in vitro. We observed impaired myogenic differentiation, including reduced fusion index and nuclei alignment. RNA sequencing analysis on the SMA myoblasts revealed activation of DNA damage pathways and innate immune activation, confirmed by the presence of 53BP1 foci and increased phosphorylation of the H2AX histones, as well as accumulation of R-loop structures and an increase of single-stranded DNA in the cytoplasm. Resolution of R-loops and DNA damage is known to cause the presence of immunogenic DNA: RNA species in the cytoplasm, activating sterile inflammation pathways. Treating control myoblasts with double-stranded DNA or a cGAS agonist phenocopied the differentiation defects in SMA myotubes. Conversely, treating SMA myoblasts with a STING inhibitor improved fusion. In summary, our results demonstrate that SMN loss exerts a cell-intrinsic impairment in muscle precursor cells, suggesting that the observed muscle dysfunction in Type II patients is not only a consequence of impaired innervation but also of the sterile inflammation caused by the genomic instability after SMN loss.

cell biology↗

bioRxiv2025

Spatial and Multiomic profiling of muscle regeneration dynamics in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a pediatric degenerative myopathy caused by the absence of functional dystrophin. As a result, DMD muscles exhibit compromised myofiber integrity and increased susceptibility to mechanical damage. In early disease stages, muscles undergo repeated cycles of degeneration and regeneration; over time, however, this regenerative capacity declines, leading to the gradual replacement of muscle tissue with fat and fibrosis. While several signaling pathways have been identified as deregulated in dystrophic muscle, the cellular and molecular mechanisms underlying this regenerative exhaustion remain to be fully elucidated. To address this, we constructed a comprehensive cellular atlas of human dystrophic muscle using high-resolution spatial transcriptomics (Visium HD), capturing the cellular crosstalk within regenerative regions. Cell-to-cell communication analysis revealed activation of Notch signaling mediated by NOTCH3 in activated satellite cells. Immunostaining confirmed elevated NOTCH3 expression in both DMD patient samples and in the mdx mouse model at late disease stages. Silencing of NOTCH3 in primary myoblasts improved myogenic differentiation, pinpointing NOTCH3-mediated signaling as a contributor to regeneration impairment. To further dissect the dynamics of regeneration and infer the gene regulatory networks governing myogenic differentiation, we integrated paired snRNA-seq and snATAC-seq data from young, adult, and aged mdx mice. This analysis identified GLIS3 upregulation as an additional barrier to effective myogenesis. GLIS3 displayed an overall increase in dystrophic muscles, while silencing experiments enhanced differentiation in myoblasts. Together, our work reveals intrinsic defects in the dystrophic stem cell compartment that emerge during disease progression and hinder the execution of the myogenic program. These findings suggest NOTCH3 and GLIS3 as potential therapeutic targets to enhance regeneration and maintain muscle integrity in DMD. This study provides a high-resolution map of the dystrophic regenerative landscape and offers a valuable resource for future translational research.

cell biology↗

bioRxiv2025

The Mutated p.H222P A-type Lamins Drive Loxl2-Mediated Extracellular Matrix Remodeling in Both Patient-Derived Cardiomyocytes and Mouse Models of Dilated Cardiomyopathy

LMNA cardiomyopathy, caused by mutations in the LMNA gene, is a severe form of dilated cardiomyopathy characterized by arrhythmias, contractile dysfunction, and increased myocardial fibrosis, which impairs left ventricular function and predisposes to heart failure. While the disease has been well characterized, a lack of insight into the pathogenesis impeded the development of therapies. We here used patient-derived LMNA p.H222P cardiomyocytes (hiPSC-CMs) and their isogenic controls and a LmnaH222P/H222P mouse model to dissect abnormal cardiac mechanisms leading to the development of the disease. We showed that LMNA p.H222P hiPSC-CMs exhibit elevated diastolic calcium levels and hypocontractility. They displayed nuclear shape abnormalities, a hallmark of LMNA cardiomyopathy, associated with altered chromosome spatial organization and gene expression profiles. Using transcriptomic analysis, we further revealed that genes related to cardiac extracellular matrix (ECM) remodeling, deposition, and components are dysregulated in both LMNA p.H222P hiPSC-CMs and mutated mice, suggesting a conserved pathogenic mechanism across species. Conversely, molecular inhibition of Loxl2, a key component of the ECM establishment, preserved the cardiac function in vivo. Taken together, our findings suggest that targeting Loxl2 could be a promising therapeutic strategy to maintain cardiac function in LMNA cardiomyopathy.

pathology↗

bioRxiv2024

SMA Type II Skeletal Muscle Treated with Nusinersen shows SMN Restoration but Mitochondrial Deficiency.

Spinal muscular atrophy (SMA) is a rare autosomal recessive developmental disorder caused by the genetic loss or mutation of the gene SMN1 (Survival of Spinal Motor Neuron 1). SMA is classically characterized by neuromuscular symptoms, including muscular atrophy, weakness of the proximal muscles, especially those of the lower extremities, and hypotonia. Although originally thought of as a purely motor neuron disease, current research has shown that most, if not all, tissues are affected, including the muscle. Until recently, muscle problems in SMA were predominantly considered a consequence of denervation due to the motor neuron death. However, recent work using muscle-specific mouse models of SMN loss, as well as skeletal stem cell specific models have shown that there are tissue specific problems in muscle due to SMN deficiency. Several years ago, SMA treatment underwent a radical transformation, with the approval of three different SMN-dependent disease modifying therapies. This includes two SMN2 splicing therapies - Risdiplam and Nusinersen, which can be administered by Type II patients that have symptom onset later in age. One main challenge for Type II SMA patients treated with Risdiplam and Nusinersen is ongoing muscle fatigue, limited mobility, and other skeletal problems, including hip dysplasia and scoliosis. To date, few molecular studies have been conducted on SMA-patient derived tissues after treatment, limiting our understanding how different organ systems react to the therapies, and what additional combination therapies may be beneficial. With this goal in mind, we collected paravertebral muscle from the surgical discard in a cohort of 8 SMA Type II patients undergoing spinal surgery for scoliosis, as well as 7 non-SMA controls with scoliosis and used RNA-sequencing to characterize their molecular profiles. We observed that despite a restoration of the SMN mRNA and protein levels in these patients - at levels at or above the controls - a subset of patients continued to have alterations in mitochondrial metabolism and other markers of cellular stress.

genetics↗