Biology subjects

Wiseman, L.

Publications and source records attributed to Wiseman, L..

3 recordsLinked to original sources

bioRxiv2020

The Endoplasmic Reticulum Proteostasis Regulator ATF6 is Essential for Human Cone Photoreceptor Development

Dysregulation of the endoplasmic reticulum (ER) Unfolded Protein Response (UPR) is implicated in the pathology of many human diseases associated with ER stress. Inactivating genetic variants in the UPR regulator Activating Transcription Factor 6 (ATF6) cause severe congenital heritable vision loss in patients by an unknown pathomechanism. To investigate this, we generated retinal organoids from patient iPSCs carrying ATF6 disease-causing variants and ATF6 null hESCs generated by CRISPR. Interestingly, we found that cone photoreceptor cells in ATF6 mutant retinal organoids lacked inner and outer segments concomitant with absence of cone phototransduction gene expression; while rod photoreceptors developed normally. Adaptive optics retinal imaging of patients with disease-causing variants in ATF6 also showed absence of cone inner/outer segment structures but preserved rod structures, mirroring the phenotypes observed in our retinal organoids. These results reveal that ATF6 is essential for the formation of human cone photoreceptors, and associated absence of cone phototransduction components explains the severe visual impairment in patients with ATF6 -associated retinopathy. Moreover, we show that a selective small molecule ATF6 activator compound restores the transcriptional activity of ATF6 disease-causing variants and stimulates the growth of cone photoreceptors in patient retinal organoids, demonstrating that pharmacologic targeting of ATF6 signaling is a therapeutic strategy that needs to be further explored for blinding retinal diseases.

developmental biology↗

bioRxiv2020

Insulin-like growth factor 2 (IGF2) protects against Huntington's disease through the extracellular disposal of protein aggregates

Impaired neuronal proteostasis is a salient feature of many neurodegenerative diseases, highlighting alterations in the function of the endoplasmic reticulum (ER). We previously reported that targeting the transcription factor XBP1, a key mediator of the ER stress response, delays disease progression and reduces protein aggregation in various models of neurodegeneration. To identify disease-modifier genes that may explain the neuroprotective effects of XBP1 deficiency, we performed gene expression profiling of brain cortex and striatum of these animals and uncovered insulin-like growth factor 2 (Igf2) as the major upregulated gene. Here we studied the impact of IGF2 signaling on protein aggregation in models of Huntingtons disease (HD) as proof-of-concept. Cell culture studies revealed that IGF2 treatment decreases the load of intracellular aggregates of mutant huntingtin and a polyglutamine peptide. These results were validated using induced pluripotent stem cells (iPSC)-derived medium spiny neurons from HD patients. The reduction in the levels of mutant huntingtin was associated with a decrease in the half-life of the intracellular protein. The decrease in the levels of abnormal protein aggregation triggered by IGF2 were independent of the activity of autophagy and the proteasome pathways, the two main routes for mutant huntingtin clearance. Conversely, IGF2 signaling enhanced the secretion of soluble mutant huntingtin species through exosomes and microvesicles involving changes in actin dynamics. Administration of IGF2 into the brain of HD mice using gene therapy led to a significant decrease in the levels of mutant huntingtin in three different animal models. Moreover, analysis of human post-mortem brain tissue, and blood samples from HD patients showed a reduction of IGF2 level. This study identifies IGF2 as a relevant factor deregulated in HD, operating as a disease modifier that buffers the accumulation of abnormal protein aggregates. One sentence summaryIGF2 reduces the load of intracellular protein aggregates through the extracellular disposal of the mutant protein.

neuroscience↗

bioRxiv2020

Small Molecule ER Proteostasis Regulators Reduce Amyloidogenic Immunoglobulin Light Chain Secretion Through an On-Target, ATF6-Independent Mechanism

The plasma cell secretion and toxic aggregation of amyloidogenic immunoglobulin light chains (LCs) causes proteotoxicity in Light Chain Amyloidosis (AL). We recently identified endoplasmic reticulum (ER) proteostasis regulators such as compound 147 that reduce secretion and aggregation of LCs implicated in AL (Plate, Cooley et al., 2016). Compound 147 promotes adaptive ER proteostasis remodeling through a mechanism involving covalent modification of multiple protein disulfide isomerases (PDIs) and subsequent activation of the ATF6 unfolded protein response (UPR) -associated transcriptional signaling pathway (Paxman, Plate et al., 2018). Here, we show that the 147-dependent reduction in amyloidogenic LC secretion from AL patient plasma cells is independent of ATF6 activation, but instead requires on-target PDI modification. Our results reveal pharmacologic targeting of PDIs as a potential strategy to ameliorate AL-associated proteotoxicity and demonstrate that 147 can influence ER proteostasis through multiple on-target mechanisms including ATF6 activation and PDI modification. IMPACT STATEMENTThis study demonstrates the broad potential for endoplasmic reticulum proteostasis regulator compounds such as 147 to influence secretory proteostasis of disease-associated proteins through multiple on target mechanisms.

biochemistry↗