Biology subjects

Rosa, J. L.

Publications and source records attributed to Rosa, J. L..

3 recordsLinked to original sources

bioRxiv2026

HERC1-mediated orphan subunit quality control maintains proteasome homeostasis and is disrupted in HERC1-associated neurodevelopmental disease

Biallelic hypomorphic variants in the E3 ubiquitin ligase HERC1 cause a neurological disorder clinically characterized by macrocephaly, dysmorphic facies, and psychomotor delay. Identifying the substrates of HERC1 is essential for understanding its biological functions and the mechanisms underlying disease-associated variants. To address this, we performed a quantitative proteomic analysis using biotinylated ubiquitin to identify HERC1 targets and examine their regulation in cells expressing HERC1 with or without ubiquitin ligase activity. This approach revealed a broad set of HERC1-dependent ubiquitylation substrates, including proteins from major multiprotein complexes such as the proteasome, the translation initiation machinery, and pathways involved in cell metabolism. Focusing on the proteasome, the most prominently represented complex, we identified several regulatory particle subunits, including PSMC6, PSME1, and PSME2. Specifically, within the 19S regulatory particle, we demonstrated that ubiquitylation of the PSMC6 subunit involves the formation of K48-linked polyubiquitin chains and depends on HERC1 activity. Other 19S subunits, such as PSMC2, PSMC4, and PSMC5, undergo a similar modification. Mechanistically, we show that HERC1 selectively recognizes unassembled subunits, promotes their ubiquitylation, and targets them for proteasomal degradation. Notably, in HERC1-deficient cells, disruption of this mechanism impaired proteasomal activity. At the disease level, quantitative proteomic analysis of the pathogenic HERC1 variant c.1448G>A (p.Gly483Glu) likewise identified altered ubiquitylation of proteasome subunits and components of the translation initiation machinery. Biochemical analyses further revealed impaired ubiquitylation of PSMC6 by the mutant HERC1 protein, associated with a loss of interaction between HERC1 and PSMC6. Together, these findings establish a link between HERC1-associated neurological disorders and defective ubiquitylation pathways. They elucidate the molecular mechanisms by which HERC1 regulates proteostasis and demonstrate how disruption of these processes contributes to disease pathogenesis, thereby highlighting potential avenues for therapeutic intervention.

molecular biology↗

bioRxiv2026

HERC1 Loss of Function Causes a Developmental Disorder with Impaired Hippocampal Function

Pathogenic variants in HERC1 are associated with a syndromic neurodevelopmental disorder characterized by macrocephaly, developmental delay, intellectual disability, and psychomotor dysfunction. Although genetic and molecular studies suggest a loss-of-function mechanism, definitive in vivo evidence that HERC1 deficiency is sufficient to cause neurodevelopmental abnormalities is lacking. Using a HERC1 knockout mouse model, we investigated the behavioural, neuronal, and synaptic consequences of complete HERC1 loss. HERC1 deficiency caused motor coordination and cognitive deficits in both sexes, while male mutants additionally displayed hyperactivity and increased anxiety-like behaviour. Histological analyses revealed selective hippocampal abnormalities, including disruption of dentate gyrus organization, whereas Purkinje cells survival and cerebellar compartmentalization remained preserved. HERC1-deficient mice exhibited a marked increase in hippocampal GABAergic interneurons, impaired maturation of dendritic spines in CA1 pyramidal neurons, and altered adult neurogenesis, indicating widespread defects in hippocampal circuit organization. Consistent with these structural abnormalities, glutamatergic synaptic components were significantly altered throughout the hippocampus. These molecular changes showed a sex-dependent pattern, with predominantly presynaptic defects in males and postsynaptic alterations in females. Despite these differences, whole-cell recordings revealed a common functional phenotype in both sexes. At both mossy fibre-CA3 and Schaffer collateral-CA1 synapses, HERC1-deficient neurons exhibited a progressive inability to sustain excitatory neurotransmission during repetitive stimulation, resulting in impaired steady-state glutamatergic transmission. Together, these findings demonstrate that loss of HERC1 function is sufficient to produce a neurodevelopmental phenotype and identify HERC1 as a critical regulator of hippocampal circuit assembly and function. Our results provide mechanistic insight into the pathogenesis of HERC1-associated disorders and establish the Herc1 knockout mouse as a preclinically relevant model for investigating disease mechanisms and therapeutic approaches.

neuroscience↗

bioRxiv2023

PI3Kalpha inhibition blocks osteochondroprogenitor specification and the hyper-inflammatory response to prevent heterotopic ossification

Heterotopic ossification (HO) occurs following mechanical trauma and burns, or congenitally in patients suffering from fibrodysplasia ossificans progressiva (FOP). Recently, we demonstrated that inhibitors of phosphatidyl-inositol 3-kinase alpha (PI3K) may be a useful therapy for patients undergoing HO. In this study, using the already marketed BYL719/Alpelisib/Piqray drug, we have further confirmed these results, detailed the underlying mechanisms of action, and optimized the timing of the administration of BYL719. We found that BYL719 effectively prevents HO even when administered up to three to seven days after injury. We demonstrate in cell cultures and in a mouse model of HO that the major actions of BYL719 are on-target effects through the inhibition of PI3K, without directly affecting ACVR1 or FOP-inducing ACVR1R206H kinase activities. In vivo, we found that a lack of PI3K in progenitors at injury sites is sufficient to prevent HO. Moreover, time course assays in HO lesions demonstrate that BYL719 not only blocks osteochondroprogenitor specification, but also reduces the inflammatory response. BYL719 inhibits the migration, proliferation and expression of pro-inflammatory cytokines in monocytes and mast cells, suggesting that BYL719 hampers the hyper-inflammatory status of HO lesions. Altogether, these results highlight the potential of PI3K inhibition as a safe and effective therapeutic strategy for HO.

molecular biology↗