Mitochondrial morphology and mtDNA content in fibroblasts from patients with different types of mucopolysaccharidosis

Mucopolysaccharidosis (MPS) is a group of inherited metabolic diseases, characterized by defects in the degradation of glycosaminoglycans and their accumulation in lysosomes. However, various secondary cellular changes also contribute to the pathomechanism of MPS. Previous studies have reached contradictory conclusions about the changes in mitochondria in MPS, from increased numbers of mitochondria to impaired activities of some mitochondrial respiratory chain enzymes to no changes in mitochondrial respiration. In this preliminary, hypothesis-generating study, mitochondrial network morphology and mitochondrial DNA (mtDNA) abundance were investigated in fibroblasts derived from patients suffering from diverse MPS types. Fluorescence microscopy and real-time PCR were used to estimate these parameters, respectively. No significant changes in the mitochondrial network morphology were detected in MPS fibroblasts relative to control cells. Decreased levels of mtDNA relative to nuclear DNA levels were evident in some (I, II, IIIA, IIID, and VI) but not all MPS types compared to control fibroblasts. The results of this study suggest that there are some, although perhaps not dramatic, impairments of mitochondrial functions in some MPS types; however, they do not provide direct evidence of mitochondrial dysfunction. Therefore, these findings should be interpreted as descriptive and exploratory, highlighting the need for further functional and mechanistic studies.