Diversity Supplement for Thompson: The Role of VPS33B in Inflammation and Sepsis

Arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome (MIM 208085) is an autosomal recessive multisystem disorder resulting from mutations in the VPS33B or VIPAR gene. ARC syndrome typically presents with cholestatic jaundice, renal tubular leak and hypotonia-related arthrogryposis. Other features variably reported include ichthyosis, mild dysmorphic signs, absent corpus callosum, recurrent infections resulting in severe metabolic acidosis, worsening nephrogenic diabetes insipidus, and lack of α granules in platelets. Most patients with ARC syndrome die with a year after birth. ARC syndrome patients often suffer recurrent infections. Infection and sepsis are the major cause of death of the ARC syndrome patients. The goal of my research is to understand the mechanism why ARC syndrome patients are susceptible to infection. Since integrin plays a key role in regulating platelet and leukocyte function, we hypothesize that impaired integrin function of platelets and/or leukocytes in the VPS33B contributes to increased mortality rate of sepsis in ARC syndrome. To test this hypothesis, we proposed two specific aims: Specific Aim 1. To investigate whether platelet VPS33B plays a role in regulating inflammation during sepsis. Specific Aim 2. To investigate whether VPS33B plays a role in regulating integrin function in leukocytes, thereby contributing to regulating inflammation in sepsis. Specific Aim 1. To investigate whether platelet VPS33B plays a role in regulating inflammation during sepsis. My mentor’s lab has recently reported that platelets protect from septic shock by inhibiting macrophage-dependent inflammation. Our preliminary data indicate that LPS-induced mortality rate were dramatically increased in the platelet-specific knockout mice compared with wild-type littermates. Thus, the Specific Aim 1 of my application is to investigate whether platelet VPS33B plays a role in regulating inflammation during sepsis. VPS33B has been shown to contribute to integrin signaling in platelets and alpha granule biosynthesis. We will first investigate increased inflammation in the platelet-specific conditional knockout mice in response to LPS is due to impaired integrin activation or alpha granule biosynthesis. These two possibilities will be tested in this aim. We have obtained integrin beta3 knockout mice. If increased inflammation in the platelet-specific conditional knockout mice in response to LPS is due to impaired activation of integrin αIIbβ3, we expect that LPS-induced inflammation will also in creased in the β3 knockout mice. We will then verify the role of integrin in inflammation using various inhibitors of integrin, including peptide RGDS and blocking antibodies against αIIbβ3. We will further investigate the mechanism by which integrin contributes to the regulation of inflammation. One hypothesis is that integrin plays a role in the aggregation between platelets and leukocytes such as macrophages. It is known that aggregates of leukocytes and platelets are increased during inflammation and sepsis. We will determine whether deletion of VPS33B in platelets will reverse this response in sepsis.