N?-lysine acetylation is an essential post-translational modification. It regulates activity, molecular stabilization and conformational assembly of targeted proteins. For more than forty years it was assumed that lysine acetylation could only occur in the cytosol and nucleus. However, in 2007, we reported the transient lysine acetylation of endoplasmic reticulum (ER) cargo proteins. Subsequent studies revealed that the ER has two acetyltransferases (ATase1 and ATase2) as well as a membrane transporter (AT-1/SCL33A1) that translocates acetyl-CoA, donor of the acetyl group for the reaction of acetylation, into the ER lumen. AT- 1/SCL33A1 is essential for the intraluminal acetylation of ER-resident and -transiting proteins. Changes in acetyl-CoA influx affect the acetylation status of the ER. Heterozygous mutations in AT-1/SCL33A1 have been identified in patients affected by a familial form of spastic paraplegia while homozygous mutations have been identified in patients affected by developmental delay of the nervous system and premature death. Finally, a duplication of AT-1/SCL33A1 has been reported in patients with autism spectrum disorder and intellectual disability. The general hypothesis of our research is that tight regulation of acetyl-CoA influx ino the ER lumen by AT-1 is essential for neuron biology. To test the above hypothesis we have generated mouse models of reduced (AT-1S113R/+) and increased (AT-1 Tg) acetyl-CoA influx into the ER. AT-1S113R/+ mice develop deficits of both the immune and nervous system. The defects of the immune system result in increased propensity to infections, aberrant inflammatory response, and increased propensity to malignancies. The defects of the nervous system result into severe motor deficits and degenerative features of the peripheral (PNS) and central (CNS) nervous system. AT-1 Tg mice display an autistic-like phenotype with behavioral deficits, impaired LTP and LTD, and increased neuronal branching. The data collected so far suggests that the ER-based acetylation machinery regulates the efficiency of protein trafficking along the secretory pathway and the induction of ERAD(II).
Specific Aim 1 will test the hypothesis that the S113R (associated with spastic paraplegia) and A110P (associated with developmental delay) mutations affect the structure of AT-1 and block post-translational assembly of the transporter in the ER membrane.
Specific Aim 2 will test the hypothesis that Atg9A acts as a sensor of acetyl-CoA levels in the ER lumen and regulates induction of ERAD(II)/autophagy down-stream of AT-1. Together, Aim 1 and Aim 2 will dissect the molecular basis of diseases associated with deficient ER acetylation.
Specific Aim 3 will test the hypothesis that abnormally high influx of acetyl-CoA into the ER lumen in AT-1 Tg mice increases the efficiency of the secretory pathway beyond physiological requirements and causes broad changes on protein expression levels in the neuron.
This Aim will dissect the molecular basis of the autism spectrum disorder and intellectual disability associated with the duplication of AT-1/SCL33A1.
This grant targets AT-1/SLC33A1, the ER membrane acetyl-CoA transporter. Heterozygous mutations on AT-1/SLC33A1 are associated with a familial form of spastic paraplegia while homozygous mutations are associated with developmental defects and premature death. Finally, a duplication of the AT-1/SLC33A1 gene is associated with autism spectrum disorder and intellectual disability. Here, we report the successful generation of mouse models that reproduce the above human diseases. By studying their phenotype, we have obtained valuable and novel information on the pathophysiology of each disease. The long-term objective of this proposal is to dissect the molecular and biochemical mechanisms associated with the above pathological events. If successful, our findings will open the way for novel therapeutic approaches.
