Biology subjects

Al Khatib, I.

Publications and source records attributed to Al Khatib, I..

3 recordsLinked to original sources

bioRxiv2022

The Ketogenic Diet Metabolite β-Hydroxybutyrate Promotes Mitochondrial Elongation via Deacetylation and Improves Autism-like Behavior in Zebrafish

The ketogenic diet (KD) is clinically beneficial and has therapeutic potential across a growing list of neurological disorders, including autism spectrum disorder (ASD). However, the underlying mechanisms mediating the benefits of the KD, which can also have undesirable side effects, remain undefined. To this end, improvements in mitochondrial morphology and function correlate with improved ASD behaviours in response to the KD, though how the KD influences mitochondrial morphology, and whether this is sufficient to improve behaviour remains unknown. Here, we investigate how beta-hydroxybutyrate (BHB), a key metabolite produced by the KD regulates mitochondrial morphology in HeLa cells, and whether this pathway could be exploited to alter phenotypes in a zebrafish model of ASD. We found that {beta}-oxidation of BHB promotes mitochondrial elongation in HeLa cells by increasing NAD+ levels, which in turn activates SIRT deacetylases that act on key regulators of both mitochondrial fusion and fission. Our data suggest that increasing NAD+ levels with its precursor, nicotinamide mononucleotide (NMN), is sufficient to promote mitochondrial hyperfusion. Finally, both BHB and NMN impact neurodevelopment in the shank3b+/- zebrafish model of ASD. Together, our findings elucidate a mechanism by which the ketogenic diet promotes mitochondrial elongation. Moreover, manipulation of this pathway may provide a novel avenue for the treatment of neurological disorders such as ASD that also may obviate potential complications of the KD in clinical practice.

molecular biology↗

bioRxiv2022

Activation of the cGAS-STING innate immune response in cells with deficient mitochondrial topoisomerase TOP1MT

The recognition that cytosolic mtDNA activates cGAS-STING innate immune signaling has unlocked novel disease mechanisms. Here, an uncharacterized variant predicted to affect TOP1MT function, P193L, was discovered in a family with multiple early-onset autoimmune diseases, including Systemic Lupus Erythematosus (SLE). Although there was no previous genetic association between TOP1MT and autoimmune disease, the role of TOP1MT as a regulator of mtDNA led us to investigate whether TOP1MT could mediate the release of mtDNA to the cytosol, where it could then activate the cGAS-STING innate immune pathway known to be activated in SLE and other autoimmune diseases. Through analysis of cells with reduced TOP1MT expression, we show that loss of TOP1MT results in release of mtDNA to the cytosol, which activates the cGAS-STING pathway. We also characterized the P193L variant for its ability to rescue several TOP1MT functions when expressed in TOP1MT knockout cells. We show that the P193L variant is not fully functional, as its re-expression at high levels was unable to rescue mitochondrial respiration deficits, and only showed partial rescue for other functions, including repletion of mtDNA replication following depletion, nucleoid size, steady state mtDNA transcripts levels, and mitochondrial morphology. Additionally, expression of P193L at endogenous levels was unable to rescue mtDNA release-mediated cGAS-STING signaling. Overall, we report a link between TOP1MT and mtDNA release leading to cGAS-STING activation. Moreover, we show that the P193L variant has partial loss of function that may contribute to autoimmune disease susceptibility via cGAS-STING mediated activation of the innate immune system.

cell biology↗

bioRxiv2021

Functional characterization of two variants in the mitochondrial topoisomerase gene TOP1MT that impact regulation of the mitochondrial genome

TOP1MT encodes a mitochondrial topoisomerase that is important for mtDNA regulation, and that is involved in mitochondrial replication, transcription and translation. Two variants predicted to affect TOP1MT function (V1 - R198C and V2 - V338L) were identified by exome sequencing of a newborn with hypertrophic cardiomyopathy. As no pathogenic TOP1MT variants had been confirmed previously, we characterized these variants for their ability to rescue several TOP1MT functions in knockout cells. Consistent with these TOP1MT variants contributing to the patient phenotype, comprehensive characterization suggests that both variants had impaired activity. Critically, neither variant was able to restore steady state levels of mitochondrial-encoded proteins, nor reduced oxidative phosphorylation when re-expressed in TOP1MT knockout cells. However, the two variants behaved differently in some respects. While the V1 variant was better at restoring transcript levels, the V2 variant was able to restore mtDNA copy number and replication. These findings suggest that the different TOP1MT variants affect distinct TOP1MT functions. Altogether, these findings begin to provide insight into the many roles that TOP1MT plays in the maintenance and expression of the mitochondrial genome, and how impairments in this important protein may lead to human pathology.

molecular biology↗