CRISPR/Cas9-mediated tissue-specific knockout and cDNA rescue using sgRNAs that target exon-intron junctions in Drosophila melanogaster

Extracellular vesicle-packaged PD-L1 impedes macrophage-mediated antibacterial immunity in preexisting malignancy

Malignancies can compromise systemic innate immunity, but the underlying mechanisms are largely unknown. Here, we find that tumor-derived small extracellular vesicles (sEVs; TEVs) deliver PD-L1 to host macrophages, thereby impeding antibacterial immunity. Mice implanted with Rab27a-knockdown tumors are more resistant to bacterial infection than wild-type controls. Injection of TEVs into mice impairs macrophage-mediated bacterial clearance, increases systemic bacterial dissemination, and enhances sepsis score in a PD-L1-dependent manner. Mechanistically, TEV-packaged PD-L1 inhibits Bruton's tyrosine kinase/PLCγ2 signaling-mediated cytoskeleton reorganization and reactive oxygen species generation, impacting bacterial phagocytosis and killing by macrophages. Neutralizing PD-L1 markedly normalizes macrophage-mediated bacterial clearance in tumor-bearing mice. Importantly, circulating sEV PD-L1 levels in patients with tumors can predict bacterial infection susceptibility, while patients with tumors treated with αPD-1 exhibit fewer postoperative infections. These findings identify a mechanism by which cancer cells dampen host innate immunity-mediated bacterial clearance and suggest targeting TEV-packaged PD-L1 to reduce bacterial infection susceptibility in tumor-bearing conditions.

Dominant missense variants in SREBF2 are associated with complex dermatological, neurological, and skeletal abnormalities

PURPOSE

We identified 2 individuals with de novo variants in SREBF2 that disrupt a conserved site 1 protease (S1P) cleavage motif required for processing SREBP2 into its mature transcription factor. These individuals exhibit complex phenotypic manifestations that partially overlap with sterol regulatory element binding proteins (SREBP) pathway-related disease phenotypes, but SREBF2-related disease has not been previously reported. Thus, we set out to assess the effects of SREBF2 variants on SREBP pathway activation.

METHODS

We undertook ultrastructure and gene expression analyses using fibroblasts from an affected individual and utilized a fly model of lipid droplet (LD) formation to investigate the consequences of SREBF2 variants on SREBP pathway function.

RESULTS

We observed reduced LD formation, endoplasmic reticulum expansion, accumulation of aberrant lysosomes, and deficits in SREBP2 target gene expression in fibroblasts from an affected individual, indicating that the SREBF2 variant inhibits SREBP pathway activation. Using our fly model, we discovered that SREBF2 variants fail to induce LD production and act in a dominant-negative manner, which can be rescued by overexpression of S1P.

CONCLUSION

Taken together, these data reveal a mechanism by which SREBF2 pathogenic variants that disrupt the S1P cleavage motif cause disease via dominant-negative antagonism of S1P, limiting the cleavage of S1P targets, including SREBP1 and SREBP2.

Cardiac RNase Z edited via CRISPR-Cas9 drives heart hypertrophy in Drosophila

Cardiomyopathy (CM) is a group of diseases distinguished by morphological and functional abnormalities in the myocardium. It is etiologically heterogeneous and may develop via cell autonomous and/or non-autonomous mechanisms. One of the most severe forms of CM has been linked to the deficiency of the ubiquitously expressed RNase Z endoribonuclease. RNase Z cleaves off the 3'-trailer of both nuclear and mitochondrial primary tRNA (pre-tRNA) transcripts. Cells mutant for RNase Z accumulate unprocessed pre-tRNA molecules. Patients carrying RNase Z variants with reduced enzymatic activity display a plethora of symptoms including muscular hypotonia, microcephaly and severe heart hypertrophy; still, they die primarily due to acute heart decompensation. Determining whether the underlying mechanism of heart malfunction is cell autonomous or not will provide an opportunity to develop novel strategies of more efficient treatments for these patients. In this study, we used CRISPR-TRiM technology to create Drosophila models that carry cardiomyopathy-linked alleles of RNase Z only in the cardiomyocytes. We found that this modification is sufficient for flies to develop heart hypertrophy and systolic dysfunction. These observations support the idea that the RNase Z linked CM is driven by cell autonomous mechanisms.

Biallelic variants in OGDH encoding oxoglutarate dehydrogenase lead to a neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities

PURPOSE

This study aimed to establish the genetic cause of a novel autosomal recessive neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities.

METHODS

We performed a detailed clinical characterization of 4 unrelated individuals from consanguineous families with a neurodevelopmental disorder. We used exome sequencing or targeted-exome sequencing, cosegregation, in silico protein modeling, and functional analyses of variants in HEK293 cells and Drosophila melanogaster, as well as in proband-derived fibroblast cells.

RESULTS

In the 4 individuals, we identified 3 novel homozygous variants in oxoglutarate dehydrogenase (OGDH) (NM_002541.3), which encodes a subunit of the tricarboxylic acid cycle enzyme α-ketoglutarate dehydrogenase. In silico homology modeling predicts that c.566C>T:p.(Pro189Leu) and c.890C>A:p.(Ser297Tyr) variants interfere with the structure and function of OGDH. Fibroblasts from individual 1 showed that the p.(Ser297Tyr) variant led to a higher degradation rate of the OGDH protein. OGDH protein with p.(Pro189Leu) or p.(Ser297Tyr) variants in HEK293 cells showed significantly lower levels than the wild-type protein. Furthermore, we showed that expression of Drosophila Ogdh (dOgdh) carrying variants homologous to p.(Pro189Leu) or p.(Ser297Tyr), failed to rescue developmental lethality caused by loss of dOgdh. SpliceAI, a variant splice predictor, predicted that the c.935G>A:p.(Arg312Lys)/p.(Phe264_Arg312del) variant impacts splicing, which was confirmed through a mini-gene assay in HEK293 cells.

CONCLUSION

We established that biallelic variants in OGDH cause a neurodevelopmental disorder with metabolic and movement abnormalities.

FIBCD1 is an endocytic GAG receptor associated with a novel neurodevelopmental disorder

Whole-exome sequencing of two patients with idiopathic complex neurodevelopmental disorder (NDD) identified biallelic variants of unknown significance within FIBCD1, encoding an endocytic acetyl group-binding transmembrane receptor with no known function in the central nervous system. We found that FIBCD1 preferentially binds and endocytoses glycosaminoglycan (GAG) chondroitin sulphate-4S (CS-4S) and regulates GAG content of the brain extracellular matrix (ECM). In silico molecular simulation studies and GAG binding analyses of patient variants determined that such variants are loss-of-function by disrupting FIBCD1-CS-4S association. Gene knockdown in flies resulted in morphological disruption of the neuromuscular junction and motor-related behavioural deficits. In humans and mice, FIBCD1 is expressed in discrete brain regions, including the hippocampus. Fibcd1 KO mice exhibited normal hippocampal neuronal morphology but impaired hippocampal-dependent learning. Further, hippocampal synaptic remodelling in acute slices from Fibcd1 KO mice was deficient but restored upon enzymatically modulating the ECM. Together, we identified FIBCD1 as an endocytic receptor for GAGs in the brain ECM and a novel gene associated with an NDD, revealing a critical role in nervous system structure, function and plasticity.

Drosophila as a Model for Human Viral Neuroinfections

The study of human neurological infection faces many technical and ethical challenges. While not as common as mammalian models, the use of Drosophila (fruit fly) in the investigation of virus–host dynamics is a powerful research tool. In this review, we focus on the benefits and caveats of using Drosophila as a model for neurological infections and neuroimmunity. Through the examination of in vitro, in vivo and transgenic systems, we highlight select examples to illustrate the use of flies for the study of exogenous and endogenous viruses associated with neurological disease. In each case, phenotypes in Drosophila are compared to those in human conditions. In addition, we discuss antiviral drug screening in flies and how investigating virus–host interactions may lead to novel antiviral drug targets. Together, we highlight standardized and reproducible readouts of fly behaviour, motor function and neurodegeneration that permit an accurate assessment of neurological outcomes for the study of viral infection in fly models. Adoption of Drosophila as a valuable model system for neurological infections has and will continue to guide the discovery of many novel virus–host interactions.