Clinical presentation and proteomic signature of patients with TANGO2 mutations

Abstract

Transport And Golgi Organization protein 2 (TANGO2) deficiency has recently been identified as a rare metabolic disorder with a distinct clinical and biochemical phenotype of recurrent metabolic crises, hypoglycemia, lactic acidosis, rhabdomyolysis, arrhythmias, and encephalopathy with cognitive decline. We report nine subjects from seven independent families, and we studied muscle histology, respiratory chain enzyme activities in skeletal muscle and proteomic signature of fibroblasts. All nine subjects carried autosomal recessive TANGO2 mutations. Two carried the reported deletion of exons 3 to 9, one homozygous, one heterozygous with a 22q11.21 microdeletion inherited in trans. The other subjects carried three novel homozygous (c.262C>T/p.Arg88*; c.220A>C/p.Thr74Pro; c.380+1G>A), and two further novel heterozygous (c.6_9del/p.Phe6del); c.11-13delTCT/p.Phe5del mutations. Immunoblot analysis detected a significant decrease of TANGO2 protein. Muscle histology showed mild variation of fiber diameter, no ragged-red/cytochrome c oxidase-negative fibers and a defect of multiple respiratory chain enzymes and coenzyme Q₁₀ (CoQ₁₀ ) in two cases, suggesting a possible secondary defect of oxidative phosphorylation. Proteomic analysis in fibroblasts revealed significant changes in components of the mitochondrial fatty acid oxidation, plasma membrane, endoplasmic reticulum-Golgi network and secretory pathways. Clinical presentation of TANGO2 mutations is homogeneous and clinically recognizable. The hemizygous mutations in two patients suggest that some mutations leading to allele loss are difficult to detect. A combined defect of the respiratory chain enzymes and CoQ₁₀ with altered levels of several membrane proteins provides molecular insights into the underlying pathophysiology and may guide rational new therapeutic interventions.

Keywords: TANGO2; fatty acid metabolism; metabolic encephalomyopathy; mitochondrial dysfunction; proteomic analysis; rhabdomyolysis.

Figure 1

A, Immunoblotting for TANGO2 protein in control fibroblasts (C) and patient fibroblasts (P) in Families 1, 2, and 4. In Family 6, TANGO2 protein levels in muscle lysates of two controls and two patients. Western blotting was performed in triplicates. B, Western blot analysis of OXPHOS complex subunits performed in total protein lysates from primary fibroblasts in the patients in Families 1 and 2, and in muscle lysates from patients and controls in Family 4

Figure 2

Proteomic profiling of patient derived fibroblasts: A, Proteomic workflow applied to identify the proteins affected by the TANGO2‐deficiency in fibroblasts. B, Volcano‐plot of proteomic findings. Red dots represent proteins showing a statistically significant decrease, whereas green dots represent proteins with a statistically significant increase in abundance. C, Subcellular distribution of affected proteins

Figure 3

Golgi apparatus (GA)‐to‐endoplasmic reticulum (ER) retrograde membrane flow. A, Immunofluorescence using anti‐GM130 antibody followed by microscopy in TANGO2 patient fibroblasts (subject 2.2) and control cells. B, To monitor GA‐ER retrograde vesicle transport the number of assembled GA at different time points upon Brefeldin (BFA) treatment (in percent) in both subjects (subject 2.1 and 2.2) and controls. C, Mean number of assembled GA at different time points upon BFA treatment (in percent) and error. Five and 10 minutes after BFA addition to the culture medium, a reduction of around 20% in the amount of cells with assembled GA was observed in both patients compared with control cells