Investigations of Cellular Stress in Development and Diseases

The overarching goal of the Unit is to establish a program that starts from the physiological genetic foundation of cellular stress–response pathways to concurrently develop clinically applicable methods for outcome measures, as well as to evaluate and discover therapeutic candidates for these pathways. The ultimate goal is to identify diseases that are integral to these pathways, and translate these findings towards optimizing their management. The basic-science component of the program will focus on investigating the regulation of the cellular integrated stress response (ISR) and related pathways as (1) mechanism(s) for variable phenotypic expressions and (2) potential therapeutic approach(es) to relevant human diseases. The clinical component will focus on using rare, pediatric, neurogenetic conditions as models for the pursuits of investigator-initiated and sponsored interventional trials.

The integrated stress response (ISR)

ISR is an evolutionarily conserved process capable of inducing pro-survival or pro-apoptotic status in cells experiencing endoplasmic-reticulum (ER) and other stresses by activating either autophagy or apoptosis. Cellular stresses, such as unfolded protein accumulation, trigger the ISR through one of the four known eIF2α kinases. The integration occurs as Ser51–phosphorylated eIF2α inhibits the guanine nucleotide exchange activity of eIF2B, halts the formation of the translation initiation ternary complex, and effectively attenuates global mRNA translation. The reduced ternary complex formation paradoxically allows for increased translation of selected mRNAs, many of whose protein products are involved in determining cell fate and may be specific in the response to the instigating stress [Sonenberg N, Hinnebusch AG Cell 2009;136:731]. As an instigator or sequela, aberrant ISR is implicated in human disorders of metabolism (diabetes), growth (skeletal dysplasia, cancer) and neurologic processes (MEHMO, Down syndrome, Alzheimer disease), amongst many others. Regulation of the ISR could provide therapeutic benefit.

CLN3 disease

CLN3 disease (also known as Batten disease or juvenile neuronal ceroid lipofuscinosis, OMIM 204200) is a rare, fatal, pediatric, neurodegenerative, lysosomal disorder for which there is no currently approved treatment. Syndromic CLN3 disease presentation includes vision loss, neurodevelopmental plateauing and decline, behavioral inflexibility and emotional lability, seizures, and motor dysfunction, as described previously and also observed in a cohort of natural history study (NCT03307304) participants at the NIH. Accumulations of lipopigment consisting of carbohydrates, lipids, metal ions, and proteins (particularly mitochondrial ATP synthase subunit C [SCMAS]) form intracellular and lysosomal deposits that autofluorescence under UV light and present as fingerprint patterns in electron microscopy. The affected CLN3 gene encodes a 468–amino acid, transmembrane, ubiquitously expressed protein implicated in many cellular pathways, whose exact function is being defined [References 2, 3].

Findings from cells and flies implicate perturbed ISR following stress induction in the CLN3–deficient compared with wild-type (WT) controls. Reduced expression of WT CLN3 lowered SH-SY5Y cell (in vitro models of neurological function) viability following treatment with the antibiotic tunicamycin [Wu D et al. Biochem Biophys Res Commun 2014;447:115], and reduced Drosophila survival following exposure to chemical inducers of oxidative stress [Tuxworth RI et al. Hum Mol Genet 2011;20:2037]. Higher eIF2α phosphorylation and expression of the ER chaperone BiP/Grp78 in fibroblast cell lines from individuals with CLN3 disease than in WT controls followed treatment with NH₄Cl (Wei H et al. Hum Mol Genet. 2008;17:469). Disturbances in the lysosome autophagic pathway may also interconnect with the ISR through the transcription factor EB (TFEB) [Martina JA et al. EMBO J 2016;35:479; Burton TD et al. J Biol Chem 2020;295:7418]. TFEB is a widely studied autophagy regulator and a treatment target of interest for conditions involving lysosomes and neurodegeneration [Cortes CJ, La Spada AR. Neurobiol Dis 2019;122:83]. Cln3 mutant mice treated with trehalose, a disaccharide activator of TFEB, had improved intracellular lipopigment accumulation, brain weight, pain sensitivity, and survival [Palmieri M et al. Nat Commun 2017;8:14338].

MEHMO syndrome (mental disability, epileptic seizures, hypogonadism/hypogenitalism, microcephaly, obesity)

MEHMO syndrome is a very rare, X-linked recessive, pediatric, multisystemic, life-limiting condition with fewer than 100 affected males reported in the literature (OMIM 300148). Life expectancy in affected individuals ranges from infancy to early adulthood. The disease locus is located on the Xp21.1-p22.13 chromosomal band. Exome sequencing identified disease-associated variants in EIF2S3, the gene encoding the gamma subunit of the translation initiation factor eIF2, which holds a central role in the ISR, as demonstrated by pathologies and diseases associated with defective phosphorylation of the alpha subunit of eIF2 (eIF2α). Diagnostic testing and disease-modifying therapies for MEHMO are not currently available.

Further understanding of cellular stress pathways such as the ISR in CLN3 disease and MEHMO syndrome models would provide insight into the underlying pathophysiology and inform novel therapeutic approaches.