Biology subjects

Kietz, C.

Publications and source records attributed to Kietz, C..

3 recordsLinked to original sources

bioRxiv2025

Hepatic gene replacement restores energy metabolism and doubles the survival in mouse model of GRACILE syndrome, a neonatal mitochondrial disease

Preclinical gene therapy studies of mitochondrial diseases remain limited due to their multisystemic manifestations and the scarcity of physiologically relevant animal models. Mutations in BCS1L, a nuclear gene encoding an assembly factor for mitochondrial complex III (CIII), are the most common cause of pediatric CIII deficiency. The most severe phenotype, GRACILE syndrome, is caused by a homozygous Finnish founder mutation (c.A232G, p.S78G). The corresponding Bcs1lp.S78G knock-in mouse model effectively recapitulates the human disease, with juvenile-onset hepatopathy, tubulopathy, growth restriction, segmental progeria, and short survival. Here, we performed recombinant adeno-associated virus (rAAV)-mediated gene replacement in this model, which features a postnatal presymptomatic window until weaning. A single intraperitoneal injection of rAAV encoding wild-type Bcs1l restored CIII assembly and activity in the liver, preventing hepatopathy. Hepatocyte-specific correction was sufficient to ameliorate hypoglycemia, improve growth, normalize systemic metabolism, and extend survival by nearly two-fold, despite persistent CIII deficiency in other tissues. Remarkably, liver-directed rescue also prevented skeletal muscle transcriptomic changes, particularly those linked to altered energy substrate utilization. These results underscore the central role of the liver in systemic energy homeostasis and growth regulation in multiorgan mitochondrial diseases and demonstrate the therapeutic potential of hepatocyte-directed gene replacement in phenotypes with prominent hepatopathy. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/677965v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@b1cf50org.highwire.dtl.DTLVardef@1a1c2e2org.highwire.dtl.DTLVardef@101bdb6org.highwire.dtl.DTLVardef@14e11e3_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

physiology↗

bioRxiv2025

Evolutionarily conserved temperature dependency leads to loss of protein O-GlcNAc in mammalian hypothermia

O-N-acetylglucosaminylation (O-GlcNAcylation) is a conserved, non-canonical glycosylation of intracellular proteins suggested to regulate a wide spectrum of fundamental cell processes and stress responses. O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) add and remove, respectively, O-GlcNAc on protein serines and threonines. O-GlcNAcylation is thought to be primarily regulated by the availability of its substrate, UDP-GlcNAc, produced by the hexosamine biosynthetic pathway (HBP). We observed a body-wide loss of O-GlcNAcylated proteins in Bcs1l mutant mice, a model of mitochondrial complex III deficiency. UDP-GlcNAc precursors glutamine, UTP and acetyl-CoA were decreased in the mutant liver but, surprisingly, UDP-GlcNAc was not consistently decreased in the organs that showed low O-GlcNAc. Neither N-acetylglucosamine supplementation nor overexpression of the HBP rate-limiting enzyme GFPT1 restored the protein O-GlcNAc levels. The Bcs1l mutant mice become hypothermic and, interestingly, earlier evidence suggest that O-GlcNAcylation depends on ambient temperature in Drosophila embryos. We found that temperature determined O-GlcNAc abundance also in adult flies of tropical and boreal Drosophila species, in the poikilothermic vertebrate zebrafish, and in cultured mammalian cells. In cultured cells, the OGT-OGA protein ratio coincided with temperature and O-GlcNAc level, providing a regulatory mechanism. Pharmacological OGA inhibition decoupled the O-GlcNAc temperature dependency in cultured cells, as did an OGA null allele in Drosophila. In Bcs1l mutant mice, O-GlcNAc levels strongly correlated with body temperature. Increasing the mouse body temperature through transgenic expression of the heat-generating mitochondrial alternative oxidase (AOX) or housing at 35{degrees}C prevented the loss of O-GlcNAc. Pharmacological restoration of O-GlcNAc in the Bcs1l mutant mice produced minimal effects, suggesting that the bulk of O-GlcNAc is dispensable in mild hypothermia. Our findings imply an evolutionarily ancient role of protein O-GlcNAcylation in temperature adaptation and, instead of protein function-specific roles, argue for a global role of O-GlcNAc in temperature control of proteostasis.

physiology↗

bioRxiv2020

drICE restrains DIAP2-mediated inflammatory signalling and intestinal inflammation

The Drosophila IAP protein, DIAP2, is a key mediator of NF-κB signalling and is required for immune activation, both locally in the intestinal epithelia and during systemic, fat body-induced responses. We have found that transgenic expression of DIAP2 induces inflammation in the intestine, but not in the fat body, indicating a need for regulating DIAP2 in microbiotic environments. We describe the Drosophila caspase drICE, a known interaction partner of DIAP2, as a regulator of DIAP2 and NF-κB signalling in the intestinal epithelium. drICE acts by cleaving, and interfering with DIAP2’s ability to ubiquitinate and, thereby, activate mediators of the NF-κB pathway. The drICE-cleaved form of DIAP2 is, moreover, unable to induce inflammation during basal conditions in the intestine. Interestingly, cleavage of DIAP2 does not interfere with pathogen-induced signalling, suggesting that drICE protects from immune responses induced by resident microbes. Accordingly, the negative regulatory effect of drICE is lost when rearing flies axenic. Hence, we show that drICE halts unwanted inflammatory signalling in the intestine by forming an inhibitory complex with DIAP2, interfering with the ability of DIAP2 to induce downstream signalling and NF-κB target gene activation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗