Biology subjects

Zampieri, S.

Publications and source records attributed to Zampieri, S..

5 recordsLinked to original sources

bioRxiv2025

HPDL is critical in human cortical development via regulation of mitochondrial functional properties

Human brain development is highly regulated by several spatiotemporal processes, which disruption can result in severe neurological disorders. Emerging evidence highlights the pivotal role of mitochondrial function as one of these fundamental pathways involved in neurodevelopment. Our study investigates the role of 4-hydroxyphenylpyruvate dioxygenase-like (HPDL) protein in cortical neurogenesis and mitochondrial activity, since mutations in the HPDL gene are associated with SPG83, a childhood-onset form of hereditary spastic paraplegia characterized by corticospinal tract degeneration and cortical abnormalities. Starting from mutant neuroblastoma cells, we demonstrated that HPDL is essential to mitochondrial respiratory chain supercomplex assembly and cellular redox balance. Moreover, transcriptomic analyses revealed dysregulated pathways related to neurogenesis, implicating HPDL role in early cortical development. To further elucidate the role of HPDL, we generated cortical neurons and organoids from SPG83 patient-derived induced pluripotent stem cells. Mutant cells exhibited premature neurogenesis at early differentiation stages, likely leading to depletion of cortical progenitors, as evidenced by decreased proliferation, slight increase of apoptosis, and unbalanced cortical type composition at later stages. Furthermore, cortical organoids derived from SPG83 patients showed impaired growth, reminding microcephaly observed in severe cases. In addition, mitochondrial morpho-functional characterization in mutant neurons confirmed disruption of OxPhos chain functionality and increased ROS generation rate. Treatment of cortical cells with two antioxidant compounds, could partially revert premature neurogenesis. In conclusion, our findings reveal a critical role for HPDL in coordinating cortical progenitor proliferation, neurogenesis, and mitochondrial function. These insights shed light on a mechanistical understanding of SPG83 pathology and underscore the therapeutic potential of targeting oxidative stress in this and related neurological disorders.

neuroscience↗

bioRxiv2025

Changes in motor unit conduction velocity after unilateral lower limb suspension and active recovery correlate with muscle ion channel gene expression

The effects of muscle disuse on the propagation of action potentials along muscle units, a key process for effective muscle activation and force production, remain poorly understood. This study aimed to investigate changes in action potential propagation and to identify biological factors influencing these changes following unilateral lower limb suspension (ULLS) and active recovery (AR). Eleven young male participants underwent 10 days of ULLS followed by 21 days of AR based on resistance exercise. Maximal force of the knee extensor muscles (MVC), High-Density surface EMG recordings and muscle biopsies of the vastus lateralis muscle were collected before ULLS, after ULLS and after AR. EMG recordings collected during submaximal isometric contractions were decomposed to estimate single motor unit conduction velocity (MU CV). Muscle biopsies were used to measure muscle fibre diameters via histochemical analysis and ion channel transcriptomic profiles via mRNA-sequencing. MVC decreased after ULLS by 29% and fully recovered after AR. MU CV decreased after ULLS and fully recovered, up to exceeding baseline values after AR. Muscle fibre diameters did not change across the interventions and showed no correlation with MU CV. Conversely, a feature importance analysis revealed that mRNA expression levels of specific ion channel genes, particularly those involved in K+ transport, correlate with MU CV at baseline and across the interventions. This study highlights the crucial role of K+ ion channels in influencing MU CV in humans, offering new insights into MU CV modulation and the mechanisms of muscle force changes after disuse and active recovery. Key pointsO_LIMuscle disuse, such as in unilateral lower limb suspension, leads to a decrease in motor unit conduction velocity (MU CV), a critical factor for muscle activation and force production. C_LIO_LIActive recovery through resistance exercise results in the full recovery of MU CV, even exceeding baseline levels. C_LIO_LIMuscle fibre diameters do not change significantly after limb suspension or active recovery and show no correlation with MU CV. C_LIO_LIConversely, ion channel mRNA expression, particularly of those related to K+ transport, correlates with MU CV and its changes following disuse and recovery. C_LIO_LIThese findings highlight K+ ion channels as a key factor in regulating MU CV in humans and provide new molecular determinants of the changes in muscle force after disuse and recovery. C_LI

physiology↗

bioRxiv2023

ERG1a K+ Channel Increases Intracellular Calcium Concentration through Modulation of Calsequestrin 1 in C2C12 Myotubes

The ERG1A K+ channel modulates the protein degradation that contributes to skeletal muscle atrophy by increasing intracellular calcium concentration ([Ca2+]i) and enhancing calpain activity, but the mechanism by which the channel regulates the [Ca2+]i is not known. Here, we have investigated the effect of human ERG1A (HERG) on [Ca2+]i in C2C12 myotubes, using Fura-2 calcium assays, immunoblot, RT-qPCR, and electrophysiology. We hypothesized that HERG would modulate L-type calcium channel activity, specifically the Cav1.1 channel known to carry signal from the sarcoplasmic membrane of skeletal muscle to the sarcomeres of the myofibrils. However, we find that HERG has no effect on the amplitude of L-type channel current nor does it affect the mRNA levels nor protein abundance of the Cav1.1 channel. Instead we find that, although the rise in [Ca2+]i (induced by depolarization) is greater in myotubes over-expressing HERG relative to controls, the difference between the KCl-stimulated Ca2+ increase in control and HERG over-expressing cells cannot be accounted for by L-type channel mediated Ca2+ influx, which suggests that HERG could modulate excitation coupled calcium entry (ECCE). Indeed, the HERG-enhanced increase in [Ca2+]i induced by depolarization is blocked by 2-APB, an inhibitor of ECCE (and SOCE). Further, we show data suggesting that HERG also modulates the activity of ryanodine receptors, a component of ECCE, as well as store operated calcium entry (SOCE). Therefore, we investigated the effect of HERG on calsequestrin1, a calcium buffering/binding protein known to modulate ryanodine receptor 1 and store operated Ca2+ entry activities. Indeed, we find that calsequestrin1 mRNA levels are decreased 0.83-fold (p<0.05) and the total protein abundance is lowered 77% (p<0.05) in myotubes over-expressing HERG relative to controls. In summary, the data show that ERG1A overexpression modulates [Ca2+]i in skeletal muscle cells by lowering the abundance of the calcium buffering/binding protein calsequestrin1.

physiology↗

bioRxiv2023

Analyzing asymmetry in brain hierarchies with a linear state-space model of resting-state fMRI data

The study of functional brain connectivity in resting-state functional magnetic resonance imaging (rsfMRI) data has traditionally focused on zero-lag statistics. However, recent research has emphasized the need to account for dynamic aspects due to the complex patterns of time-varying co-activations among brain regions. In this regard, the importance of non-zero-lag statistics in studying complex brain interactions has been emphasized, both in terms of modeling and data analysis. Here, we show how a time-lag description is incorporated within the framework of dynamic causal modeling (DCM) resulting in an asymmetric state interaction matrix known as effective connectivity (EC). Asymmetry in EC is conventionally associated with the directionality of interactions between brain regions and is frequently employed to distinguish between incoming and outgoing node connections. We will revisit this interpretation by employing a decomposition of the EC matrix. This decomposition enables us to isolate the steady-state differential crosscovariance matrix, which is responsible for modeling the information flow and introducing time irreversibility. In other words, by modeling the off-diagonal part of the differential covariance, the system landscape may exhibit a curl steady-state flow component that breaks detailed balance and diverges the dynamics from equilibrium. Our empirical results reveal that only the outgoing strengths of the EC matrix relate with the flow described by the differential cross-covariance, while the so-called incoming strengths are primarily driven by the zero-lag covariance, specifically the precision matrix, thus reflecting conditional independence rather than directionality.

neuroscience↗

bioRxiv2022

NAD+ repletion with niacin counteracts cancer cachexia

Cachexia is a debilitating wasting syndrome and highly prevalent comorbidity in cancer patients. It manifests especially with energy and mitochondrial metabolism aberrations that promote tissue wasting. We recently identified nicotinamide adenine dinucleotide (NAD+) loss to associate with muscle mitochondrial dysfunction in cancer hosts. In this study we confirmed that depletion of NAD+ and downregulation of Nrk2, an NAD+ biosynthetic enzyme, are common features of different mouse models and cachectic cancer patients. Testing NAD+ repletion therapy in cachectic mice revealed that NAD+ precursor, vitamin B3 niacin, efficiently corrected tissue NAD+ levels, improved mitochondrial metabolism and ameliorated cancer- and chemotherapy-induced cachexia. To examine NAD+ metabolism in a clinical setting, we showed that the low expression of NRK2 in cancer patients correlated with metabolic abnormalities underscoring the significance of NAD+ in the pathophysiology of human cancer cachexia. Overall, our results propose a novel therapy target, NAD+ metabolism, for cachectic cancer patients.

molecular biology↗