Hamed Jafar-Nejad Lab

Glycosylation is one of the most common post-translational modifications of proteins and plays major roles in various aspects of cellular and organismal biology. Our laboratory uses Drosophila and mouse genetics combined with cell culture and biochemical approaches to understand how glycosylation and deglycosylation regulate animal development and contribute to human disease pathophysiology. Our initial focus in this area was understanding how O-linked glycosylation of Notch EGF repeats regulates the Notch signaling pathway. In collaboration with carbohydrate biochemists, we identified POGLUT1, the enzyme responsible for O-glucose addition to Notch and other secreted and extracellular proteins, and functionally characterized POGLUT1 and its downstream xylosyltransferases in Notch signaling. Through collaboration with muscle biologists, we also identified a novel form of limb-girdle muscular dystrophy (LGMDR21) caused by POGLUT1 mutations and elucidated POGLUT1's critical role in muscle stem cell development and maintenance.

A major focus of our current work is on identifying dosage-sensitive genetic modifiers of rare diseases in animal models, then establishing the most promising candidates as potential therapeutic targets. This approach has proven fruitful for Alagille syndrome (ALGS), a multisystem developmental disorder characterized by cholestasis caused by impaired development of the biliary tree. Through genetic studies, we established several mouse models for this disease and discovered that reducing the dosage of two genes—Poglut1, encoding a glycosyltransferase, and Sox4, encoding a transcription factor—suppresses ALGS liver phenotypes. Using preclinical therapeutic studies in postnatal mice, we have shown that silencing Poglut1 with an antisense oligonucleotide (ASO) or silencing Sox4 with an adeno-associated virus (AAV) vector can dramatically enhance biliary tree development and ameliorate ALGS liver disease. Current work aims to elucidate the molecular mechanisms underlying the observed rescue, advancing the therapies towards clinical trials, identifying other potential genetic suppressors of the ALGS liver phenotypes, and exploring whether these strategies might be beneficial beyond ALGS.

In parallel, we study enzymes involved in N-glycosylation and de-N-glycosylation, which play major roles in animal development and homeostasis and are impaired in congenital disorders of glycosylation and deglycosylation. Our studies in this area have led to the identification of several signaling pathways and processes—including BMP signaling, AMPK signaling, as well as intestinal and systemic innate immune response—regulated by the de-N-glycosylation enzyme NGLY1. Current work aims to extend these studies to additional components of the N-glycosylation machinery, interrogating their roles in regulating the above-mentioned processes and shaping the host’s response to gut microbiota. Our hope is that these mechanistic studies might help shed light on the pathophysiology of congenital disorders of glycosylation and deglycosylation, and offer potential therapeutic approaches for these understudied diseases.

For details about specific research areas and ongoing projects, please visit our Projects page.