Naturally occurring cone disorder in nonhuman primates

Achromatopsia is form of congenital retinal degeneration characterized by the loss of cone photoreceptor function, resulting in dramatic loss of visual acuity. Mouse models of cone disorders are available; however, clinical translation of these models is limited, as cone density in the murine retina is much less than that of humans. In this episode, Sara Thomasy and Ala Moshiri discuss the identification and characterization of a naturally occurring mutation in nonhuman primates that results in features that mirror human achromatopsia. This nonhuman primate model has high potential for therapeutic testing and optimization of gene editing and of cone cell replacement strategies.

Sphingolipid desaturase DEGS1 linked to rare leukodystrophy

Leukodystrophies are rare congenital disorders that affect the white matter of the brain, resulting in a range of neurological presentations. Several leukodystrophy-associated genes have been identified; however, the etiology of many cases remains unclear. In this episode, Aurora Pujol, Ali Fatemi, Marc Patterson, Javier Terriente, and Carlos Casasnovas discuss their collaboration, which led to the identification of a mutation in the endoplasmic reticulum lipid desaturase DEGS1 as the underlying cause of a leukodystrophy in 19 patients from 13 unrelated families. The mutation was linked to an imbalance of the DEGS1 substrate dihydroceramide and ceramide. In a DEGS1 knockdown zebrafish model, treatment with fingolimod reduced the imbalance between dihydroceramide and ceramide, decreased locomotor disability, and increased oligodendrocyte myelination, suggesting this strategy be explored for mutant DESG1-related disease.

Mast cell engagement of γδ T cells protects against viral infection

The skin is an important barrier to infections and contains resident immune cells poised to respond to pathogens. Tissue-resident mast cells are critical for pathogen surveillance and initial response. In this episode, Ashley St. John discusses her work, which reveals a previously unrecognized interaction between mast cells and γδ T cells in the skin that is critical for clearance of dengue virus (DENV). The results of this study indicate that mast cells serve as nonconventional antigen-presenting cells that are poised to activate γδ T cells early during viral infection and limit disease.

Strain aneuploidy underlies fluconazole resistance in human cryptococcal meningitis

Cryptococcal meningitis (CM) is an opportunistic fungal infection that primarily affects immunocompromised individuals, particularly those with HIV/AIDS. In resource-limited countries, patients often receive antifungal drug fluconazole monotherapy; however, long-term outcomes, even at high doses, are poor. In this episode, Neil Stone and colleagues observed treatment response in a cohort of patients with HIV-associated CM given fluconazole alone or in combination with flucytosine. Patients treated with fluconazole monotherapy had an increase in resistant subpopulations in the CSF; however, combination prevented expansion of resistant populations. Fluconazole-resistant strains had high rates of aneuploidy characterized predominant diploidy of drug efflux pump-containing chromosome 1. Together, these results support combination therapy as a successful strategy for suppressing heteroresistance.

Screen identifies group A streptococcus genes important for necrotizing disease

Group A streptococcus (GAS) is a common cause of life-threating necrotizing fasciitis and myositis. Necrotizing disease is relatively rare; however, it has a high rate of mortality, and affected limbs must often be amputated. In this episode, James Musser and colleagues use transposon-directed insertion-site sequencing (TraDIS) to identify GAS genes required for the development of necrotizing myositis in a nonhuman primate model. In particular, several bacterial transporters were determined to be required for infection, and thereby represent potential therapeutic targets for this devastating disease.