The European landscape for gene therapies in orphan diseases: 6-year experience with the EMA Committee for Orphan Medicinal Products.

In 2000, the European Union (EU) introduced the orphan pharmaceutical legislation to incentivize the development of medicinal products for rare diseases. The Committee for Orphan Medicinal Products (COMP), the European Medicines Agency committee responsible for evaluation of applications for orphan designation (OD), received an increasing flow of applications in the field of gene therapies over the last years. Here, the COMP has conducted a descriptive analysis of applications regarding gene therapies in non-oncological rare diseases, with respect to (a) targeted conditions and their rarity, (b) characteristics of the gene therapy products proposed for OD, with a focus on the type of vector used, and (c) regulatory aspects pertaining to the type of sponsor and development, by examining the use of available frameworks offered in the EU such as protocol assistance and PRIME. It was noted that gene therapies are being developed by sponsors from different backgrounds. Most conditions being targeted are monogenic, the most common being lysosomal disorders, and with a very low prevalence. Generally, adeno-associated viral vectors were being used to deliver the transgene. Finally, sponsors are not frequently using the incentives that may support the development and the reasons for this are unclear.

Sex specific activation of the ERα axis of the mitochondrial UPR (UPRmt) in the G93A-SOD1 mouse model of familial ALS.

The mitochondrial unfolded protein response (UPRmt) is a transcriptional program aimed at restoring proteostasis in mitochondria. Upregulation of mitochondrial matrix proteases and heat shock proteins was initially described. Soon thereafter, a distinct UPRmt induced by misfolded proteins in the mitochondrial intermembrane space (IMS) and mediated by the estrogen receptor alpha (ERα), was found to upregulate the proteasome and the IMS protease OMI. However, the IMS-UPRmt was never studied in a neurodegenerative disease in vivo. Thus, we investigated the IMS-UPRmt in the G93A-SOD1 mouse model of familial ALS, since mutant SOD1 is known to accumulate in the IMS of neural tissue and cause mitochondrial dysfunction. As the ERα is most active in females, we postulated that a differential involvement of the IMS-UPRmt could be linked to the longer lifespan of females in the G93A-SOD1 mouse. We found a significant sex difference in the IMS-UPRmt, because the spinal cords of female, but not male, G93A-SOD1 mice showed elevation of OMI and proteasome activity. Then, using a mouse in which G93A-SOD1 was selectively targeted to the IMS, we demonstrated that the IMS-UPRmt could be specifically initiated by mutant SOD1 localized in the IMS. Furthermore, we showed that, in the absence of ERα, G93A-SOD1 failed to activate OMI and the proteasome, confirming the ERα dependence of the response. Taken together, these results demonstrate the IMS-UPRmt activation in SOD1 familial ALS, and suggest that sex differences in the disease phenotype could be linked to differential activation of the ERα axis of the IMS-UPRmt.

Silencing of frataxin gene expression triggers p53-dependent apoptosis in human neuron-like cells.

Friedreich's ataxia (FRDA) is an autosomal recessive disease caused by mutations that produce a deficiency in frataxin. Despite the importance of neurodegeneration in FRDA, little is known about the consequences of frataxin deficiency in neuronal cells. Here we describe a neuronal cell model for FRDA based on the use of lentiviral vectors that carry minigenes encoding frataxin-specific shRNAs that silence the expression of this gene. These lentivectors can knockdown frataxin expression in human neuroblastoma SH-SY5Y cells, which results in large-scale cell death in differentiated neuron-like cells but not in undifferentiated neuroblastoma cells. Frataxin-deficient neuron-like cells appear to die through apoptosis that is accompanied by up-regulation of p53, PUMA and Bax and activation of caspase-3. No significant autophagy is observed in frataxin-deficient neuron-like cells and the pharmacological activation of autophagy does not significantly increase neuronal cell death in response to the frataxin deficiency. Cell death triggered by frataxin knockdown can be impaired by interference with p53, caspase inhibitors and gene transfer of FXN. These results suggest that frataxin gene silencing in human neuron-like cells may constitute a useful cell model to characterize the molecular changes triggered by frataxin deficiency in neurons, as well as to search for therapies that may protect against neurodegeneration.

ALS-FTLD-linked mutations of SQSTM1/p62 disrupt selective autophagy and NFE2L2/NRF2 anti-oxidative stress pathway.

Macroautophagy (autophagy) is a key catabolic pathway for the maintenance of proteostasis through constant digestion of selective cargoes. The selectivity of autophagy is mediated by autophagy receptors that recognize and recruit cargoes to autophagosomes. SQSTM1/p62 is a prototype autophagy receptor, which is commonly found in protein aggregates associated with major neurodegenerative diseases. While accumulation of SQSTM1 implicates a disturbance of selective autophagy pathway, the pathogenic mechanism that contributes to impaired autophagy degradation remains poorly characterized. Herein we show that amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD)-linked mutations of TBK1 and SQSTM1 disrupt selective autophagy and cause neurotoxicity. Our data demonstrates that proteotoxic stress activates serine/threonine kinase TBK1, which coordinates with autophagy kinase ULK1 to promote concerted phosphorylation of autophagy receptor SQSTM1 at the UBA domain and activation of selective autophagy. In contrast, ALS-FTLD-linked mutations of TBK1 or SQSTM1 reduce SQSTM1 phosphorylation and compromise ubiquitinated cargo binding and clearance. Moreover, disease mutation SQSTM1G427R abolishes phosphorylation of Ser351 and impairs KEAP1-SQSTM1 interaction, thus diminishing NFE2L2/Nrf2-targeted gene expression and increasing TARDBP/TDP-43 associated stress granule formation under oxidative stress. Furthermore, expression of SQSTM1G427R in neurons impairs dendrite morphology and KEAP1-NFE2L2 signaling. Therefore, our results reveal a mechanism whereby pathogenic SQSTM1 mutants inhibit selective autophagy and disrupt NFE2L2 anti-oxidative stress response underlying the neurotoxicity in ALS-FTLD.Abbreviations: ALS: amyotrophic lateral sclerosis; FTLD: frontotemporal lobar degeneration; G3BP1: GTPase-activating protein (SH3 domain) binding protein 1; GSTM1: glutathione S-transferase, mu 1; HMOX/HO-1: Heme oxygenase 1; IP: immunoprecipitation; KEAP1: kelch-like ECH associated protein 1; KI: kinase inactive; KIR: KEAP1 interaction region; KO: knockout; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MBP: maltose binding protein; NBR1: NBR1, autophagy cargo receptor; NFE2L2/Nrf2: nuclear factor, erythroid derived 2, like 2; NQO1: NAD(P)H quinone dehydrogenase 1; SQSTM1/p62: sequestosome 1; SOD1: superoxide dismutase 1, soluble; S.S.: serum starvation; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK binding kinase 1; UBA: ubiquitin association; ULK1: unc-51 like autophagy activating kinase 1; WT: wild type.

Parkin is a disease modifier in the mutant SOD1 mouse model of ALS.

Mutant Cu/Zn superoxide dismutase (SOD1) causes mitochondrial alterations that contribute to motor neuron demise in amyotrophic lateral sclerosis (ALS). When mitochondria are damaged, cells activate mitochondria quality control (MQC) mechanisms leading to mitophagy. Here, we show that in the spinal cord of G93A mutant SOD1 transgenic mice (SOD1-G93A mice), the autophagy receptor p62 is recruited to mitochondria and mitophagy is activated. Furthermore, the mitochondrial ubiquitin ligase Parkin and mitochondrial dynamics proteins, such as Miro1, and Mfn2, which are ubiquitinated by Parkin, and the mitochondrial biogenesis regulator PGC1α are depleted. Unexpectedly, Parkin genetic ablation delays disease progression and prolongs survival in SOD1-G93A mice, as it slows down motor neuron loss and muscle denervation and attenuates the depletion of mitochondrial dynamics proteins and PGC1α. Our results indicate that Parkin is a disease modifier in ALS, because chronic Parkin-mediated MQC activation depletes mitochondrial dynamics-related proteins, inhibits mitochondrial biogenesis, and worsens mitochondrial dysfunction.

Exploring new pathways of neurodegeneration in ALS: the role of mitochondria quality control.

Neuronal cells are highly dependent on mitochondria, and mitochondrial dysfunction is associated with neurodegenerative diseases. As perturbed mitochondrial function renders neurons extremely sensitive to a wide variety of insults, such as oxidative stress and bioenergetic defects, mitochondrial defects can profoundly affect neuronal fate. Several studies have linked ALS with mitochondrial dysfunction, stemming from observations of mitochondrial abnormalities, both in patients and in cellular and mouse models of familial forms of ALS. Mitochondrial changes have been thoroughly investigated in mutants of superoxide dismutase 1 (SOD1), one of the most common causes of familial ALS, for which excellent cellular and animal models are available, but recently evidence is emerging also in other forms of ALS, both familial and sporadic. Mitochondrial defects in ALS involve many critical physiopathological processes, from defective bioenergetics to abnormal calcium homeostasis, altered morphology and impaired trafficking. In this review, we summarize established evidence of mitochondrial dysfunction in ALS, especially in SOD1 mutant models of familial ALS. The main focus of the review is on defective mitochondrial quality control (MQC) in ALS. MQC operates at multiple levels to clear damaged proteins through proteostasis and to eliminate irreparably damaged organelles through mitophagy. However, since ALS motor neurons progressively accumulate damaged mitochondria, it is plausible that the MQC is ineffective or overwhelmed by excessive workload imposed by the chronic and extensive mitochondrial damage. This article is part of a Special Issue entitled ALS complex pathogenesis.

Mitochondrial hexokinase II promotes neuronal survival and acts downstream of glycogen synthase kinase-3.

Mitochondrial alterations are detected in most neurodegenerative disorders and may contribute to the dysfunction and demise of neuronal cells. Because glycogen synthase kinase-3 (GSK-3) is considered to be a critical factor in regulating neuronal cell survival and death, we studied the effects of modulating GSK-3 activity in cultured neurons treated with the mitochondrial inhibitor, rotenone. Interestingly, chronic inhibition of GSK-3 protects against rotenone-induced apoptosis in cultured neuronal cells. In an attempt to elucidate the molecular mechanisms underlying this neuroprotection, we demonstrated that chronic inhibition of GSK-3 reprograms the metabolism of neuronal cells, leading to an enhancement of glycolysis. This effect was accompanied by the induction and accumulation of hexokinase II (HKII) in the mitochondria. Interfering with either the mitochondrial binding of HKII or HKII expression significantly diminished the neuroprotection evoked by GSK-3 inhibition, and importantly, HKII overexpression is sufficient to protect against rotenone-induced cell death. Thus, mitochondrial HKII is a promoter of neuronal survival under the regulation of GSK-3. Furthermore, the neuroprotective effect of HKII may be relevant to neurodegenerative diseases in which glucose hypometabolism and mitochondrial dysfunction are prominent features.

Functional recovery in a Friedreich's ataxia mouse model by frataxin gene transfer using an HSV-1 amplicon vector.

There is currently no effective treatment for Friedreich's ataxia (FA), the most common of the hereditary ataxias. The disease is caused by mutations in FRDA that drastically reduce expression levels of the mitochondrial protein frataxin. In FA animal models, a key difficulty is obtaining the precise levels of frataxin expression in the appropriate tissues to provoke pathology without early lethality. To develop strategies to circumvent these problems, conditional frataxin transgenic mice have been generated. We now show that frataxin expression can be eliminated in neurons from these loxP[frda] mice by infection with CRE-expressing herpes simplex virus type 1 (HSV-1) amplicon vectors. We have also achieved in vivo delivery by stereotaxic injection of these CRE-expressing vectors into the brainstem of loxP[frda] mice to generate a localized gene knockout model. These mice develop a behavioral deficit in the rotarod assay detectable after 4 weeks, and when re-injected with HSV-1 amplicon vectors expressing human frataxin complementary DNA (cDNA) exhibit behavioral recovery as early as 4 weeks after the second injection. To the best of our knowledge, this is the first proof of principle of recovery of neurological function by a therapeutic agent aimed at correcting frataxin deficiency.