Biology subjects

Porro, A.

Publications and source records attributed to Porro, A..

7 recordsLinked to original sources

bioRxiv2026

Comprehensive classification of HCN1 variants linked to neurodevelopmental disorders with and without epilepsy

Hyperpolarization-activated cyclic nucleotide-gated 1 channels (HCN1) mediate the Ih cationic current and play a central role in regulating neuronal excitability and synaptic integration. HCN1 is predominantly expressed in the neocortex and hippocampus. Pathogenic variants in HCN1 have been increasingly identified in individuals presenting with a broad spectrum of epileptic disorders, ranging from severe developmental and epileptic encephalopathy (DEE) to milder epilepsies. Here, we used patch-clamp electrophysiology in combination with confocal imaging in HEK293 cells to functionally characterize 43 HCN1 variants found in patients presenting with neurodevelopmental disorders, with or without epilepsy. Based on their biophysical properties, we defined four functional classes: (I) low or no current, (II) hyperpolarizing (i.e. left) shift in voltage dependence, (III) depolarizing (i.e. right) shift in voltage dependence, and (IV) generation of an instantaneous current. Integration of this functional classification with detailed clinical data from a cohort of 49 patients revealed a striking genotype-phenotype correlation. Loss-of-function variants were strongly enriched among individuals without epilepsy or with milder generalized phenotypes, whereas gain-of-function and mixed variants were predominantly associated with epilepsy, including all cases of DEE. Notably, non-epileptic cases clustered within a subgroup of loss-of-function variants affecting the selectivity filter. We further show that allosteric modulators, including the peptides NB6 and TRIP8bnano and the small molecule J&J12e, normalize the functional properties of mutant HCN1 channels in three classes. These findings establish a clinically relevant framework for interpreting HCN1 gain- and loss-of-function variants suggesting that the direction of channel dysfunction is a major determinant of epilepsy risk and severity.

pathology↗

bioRxiv2025

USP7 deubiquitinase stabilizes FAN1 to support DNA crosslink repair and suppress CAG repeat expansion

Human FAN1 is a structure-specific endonuclease critical for the repair of DNA interstrand crosslinks (ICLs) and the excision of extrahelical CAG repeats-whose pathological expansion underlies Huntingtons disease (HD), a progressive and currently incurable neurodegenerative disorder. However, mechanisms of post-translational regulation of FAN1 are still largely unknown. Here, we identify the ubiquitin-specific protease 7 (USP7) as new interactor of FAN1. USP7 stabilizes FAN1 protein levels in a deubiquitination-dependent manner, preventing FAN1 from proteasomal degradation. Consequently, we demonstrate that USP7 depletion leads to reduced chromatin association of FAN1 and increased cellular hypersensitivity following ICL damage. Moreover, we find that loss of USP7 accelerates CAG repeat expansion in an HD cellular model. Collectively, our findings establish USP7 as a critical regulator of FAN1 activity in the maintenance of genome stability, highlighting potential therapeutic opportunities for cancer and HD.

molecular biology↗

bioRxiv2025

Animal-free recombinant nanobody rescues HCN4 channel deficit in sinus node dysfunction

Hyperpolarization-activated cyclic nucleotide-gated channels (HCN1-4) control cardiac and neuronal firing and their dysfunction leads to cardiac arrythmias (HCN4), epilepsy (HCN1) and chronic pain (HCN2). Prompted by the urgent need for HCN subtype-specific treatments, we screened a recombinant nanobody library in search of HCN4-specific binders. Here we show that nanobody 5 (NB5) binds to the extracellular side of HCN4 with high specificity and nanomolar affinity and activates the channel by a non-canonical electromechanical coupling path. In ex vivo and in vitro experiments, NB5 acts as an agonist of the pacemaker current If, increasing the firing rate of rabbit cardiac pacemaker myocytes and of human derived cardiomyocytes. Notably, NB5 rescued the effects of a LOF HCN4 mutation causing sinus node dysfunction in a patient. Our work illustrates that animal-free recombinant nanobodies have strong potential as next generation modulators for clinical application in symptomatic bradycardia.

biophysics↗

bioRxiv2024

A synthetic potassium channel reduces oxidative stress 1 via cellular adaptronics

Aerobic metabolism is crucial for human life but reactive oxygen species (ROS) byproducts cause cellular toxicity. Although antioxidant defenses usually maintain ROS levels within a safe range, ROS production can exceed the buffering capacity of cells, causing oxidative stress and disease. Inspired by the principle of adaptronics, we created a synthetic potassium channel that senses cellular ROS levels and mitigates oxidative stress by modulating membrane potential. Engineered from TASK1 channel, ROSTASK1 is sensitive to supraphysiological ROS levels, imposing restorative membrane potential changes on cells or organelles under oxidative stress. We also engineered a blue-light sensitive ROSTASK1 to achieve optogenetic control. In proof-of-concept experiments, mitochondrially-delivered ROSTASK1 rescued ROS overproduction in myoblasts from a Leigh syndrome patient and ROSTASK1 abolished chronic pain-like behavior in mouse models of inflammation and nerve injury. Thus, by functioning as both a sensor and modulator of ROS levels, ROSTASK1 provides a self-healing system during oxidative stress.

biophysics↗

bioRxiv2024

The PIN1-p38-CtIP signaling axis protects stalled replication forks from deleterious degradation

Human CtIP plays a critical role in homologous recombination (HR) by promoting the resection of DNA double-strand breaks. Moreover, CtIP maintains genome stability through protecting stalled replication forks from nucleolytic degradation. However, the upstream signaling mechanisms governing the molecular switch between these two CtIP-dependent processes remain largely elusive. Here, we show that phosphorylation of CtIP by the p38 stress kinase and subsequent PIN1-mediated CtIP cis-to-trans isomerization is required for fork stabilization but dispensable for HR. We found that stalled forks are degraded in cells expressing non-phosphorylatable CtIP or lacking PIN1-p38 activity, while expression of a CtIP trans-locked mutant overcomes the requirement for PIN1-p38 in fork protection. We further reveal that Brca1-deficient mammary tumor cells that have acquired PARPi resistance regain chemosensitivity after PIN1 or p38 inhibition. Collectively, our findings identify the PIN1-p38-CtIP signaling pathway as a critical regulator of replication fork integrity.

molecular biology↗

bioRxiv2021

Seizures, behavioral deficits and adverse drug responses in two new genetic mouse models of HCN1 epileptic encephalopathy

De novo mutations in voltage- and ligand-gated channels have been associated with an increasing number of cases of developmental and epileptic encephalopathies, which often fail to respond to classic antiseizure medications. Here, we examine two knock-in mouse models replicating de novo mutations in the HCN1 voltage-gated channel gene, p.G391D and p.M153I (Hcn1G380D/+ and Hcn1M142I/+ in mouse), associated with severe drug-resistant neonatal- and childhood-onset epilepsy, respectively. Heterozygous mice from both lines displayed spontaneous generalized tonic-clonic seizures. Hcn1G380D/+ animals had an overall more severe phenotype, with pronounced alterations in the levels and distribution of HCN1 protein, including disrupted targeting to the axon terminals of basket cell interneurons. In line with clinical reports from HCN1 patients, administration of the antiepileptic Na+ channel antagonists lamotrigine and phenytoin resulted in the paradoxical induction of seizures in both lines, consistent with an effect to further impair inhibitory neuron function. We also show that these variants can render HCN1 channels unresponsive to classic antagonists, indicating the need to screen mutated channels to identify novel compounds with diverse mechanism of action. Our results underscore the need to tailor effective therapies for specific channel gene variants, and how strongly validated animal models may provide an invaluable tool towards reaching this objective.

neuroscience↗

bioRxiv2018

Structure-guided design of a cell penetrating peptide preventing cAMP modulation of HCN channels

The auxiliary subunit TRIP8b prevents cAMP activation of HCN channels by antagonizing its binding to their cyclic-nucleotide binding domain (CNBD). By determining an NMR-derived structure of the complex formed by the HCN2 channel CNBD and a minimal TRIP8b fragment, TRIPnano, we show here a bipartite interaction between the peptide and CNBD which prevents cAMP binding in two ways: through direct competition for binding at the distal C-helix of the CNBD; and through an allosteric reduction in cAMP affinity induced by TRIP8b binding to the CNBD N-bundle loop. TRIPnano abolishes cAMP binding in all three isoforms, HCN1, HCN2 and HCN4 and can be used to prevent cAMP stimulation in native f-channels. Application of TRIP8bnano, or its delivery via a cell-penetrating sequence, in sinoatrial node myocytes, selectively inhibits beta-adrenergic stimulation of the native If current and mimics the physiological concentrations of acetylcholine leading to a 30% reduction in the spontaneus rate of action potential firing.

physiology↗