Carney triad, SDH-deficient tumors, and Sdhb+/- mice share abnormal mitochondria

Abstract

Carney triad (CTr) describes the association of paragangliomas (PGL), pulmonary chondromas, and gastrointestinal (GI) stromal tumors (GISTs) with a variety of other lesions, including pheochromocytomas and adrenocortical tumors. The gene(s) that cause CTr remain(s) unknown. PGL and GISTs may be caused by loss-of-function mutations in succinate dehydrogenase (SDH) (a condition known as Carney-Stratakis syndrome (CSS)). Mitochondrial structure and function are abnormal in tissues that carry SDH defects, but they have not been studied in CTr. For the present study, we examined mitochondrial structure in human tumors and GI tissue (GIT) of mice with SDH deficiency. Tissues from 16 CTr tumors (n=12), those with isolated GIST (n=1), and those with CSS caused by SDHC (n=1) and SDHD (n=2) mutations were studied by electron microscopy (EM). Samples of GIT from mice with a heterozygous deletion in Sdhb (Sdhb(+) (/-), n=4) were also studied by EM. CTr patients presented with mostly epithelioid GISTs that were characterized by plump cells containing a centrally located, round nucleus and prominent nucleoli; these changes were almost identical to those seen in the GISTs of patients with SDH. In tumor cells from patients, regardless of diagnosis or tumor type, cytoplasm contained an increased number of mitochondria with a 'hypoxic' phenotype: mitochondria were devoid of cristae, exhibited structural abnormalities, and were of variable size. Occasionally, mitochondria were small and round; rarely, they were thin and elongated with tubular cristae. Many mitochondria exhibited amorphous fluffy material with membranous whorls or cystic structures. A similar mitochondrial hypoxic phenotype was seen in Sdhb(+) (/-) mice. We concluded that tissues from SDH-deficient tumors, those from mouse GIT, and those from CTr tumors shared identical abnormalities in mitochondrial structure and other features. Thus, the still-elusive CTr defect(s) is(are) likely to affect mitochondrial function, just like germline SDH-deficiency does.

Keywords: Carney triad; GIST; mitochondria; succinate dehydrogenase.

Figure 1

(A–D) Gastric stromal sarcoma (Case No. 1). Luxuriant filopodal cell borders (marked as F). Numerous glycogen granules (arrow) and prominent nucleoli (B). Mitochondria show abnormal cristae structure (*) (and inset B). Moderately increased numbers of mitochondria (C – D), all showing abnormal morphology; no cristae (*). (E – F) Gastric stromal sarcoma (Case No 2, specimen 6) Fewer numbers of oval and spindle cells with heavily lobulated nuclei (E, arrow) intracytoplasmic filamentous aggregates, slender surface filopodia (F) and a few short intercellular attachments were present. Polygonal and spindle cells were packed with cystic-looking mitochondria (*) without cristae and with intra-mitochondrial membranous inclusions (H, *). (G–I) CTr Gastrointestinal Stromal Tumors (Case no 2, specimen 6). Oval and spindle cells are in close apposition. Slender filopodia (F) are evident with few short intercellular attachments. The cytoplasm contains strands of rough endoplasmic reticulum (RER), branching ER, intermediate filaments and increased numbers of mitochondria (*). Mitochondria exhibit variable sizes and structural abnormalities – some are small and round, others are thin and elongated with tubular cristae. Many mitochondria have partial to complete loss of cristae and exhibit amorphous amorphous material containing membranous whorls or cystic structures.

Figure 2

Ultrastructural features of a Paraganglioma (PGL) exhibiting many abnormal mitochondria (*) and dense core granules (arrowheads) (Case No 1).

Figure 3

(A–D) Ultrastructural features of a Paraganglioma (PGL) (Case No 2) exhibiting polygonal and spindle cells packed with cystic-looking mitochondria (*) without cristae and with intra-mitochondrial membranous inclusions. The cell surfaces are smooth. (E–F) Lung chondroma, majority of mitochondria are devoid of cristae (*). Presence of leaky chromatin in the chondroma (E, arrow).

Figure 4

Ultrastructural features of (A) wild type and (B) Sdhb^+/− 12-month old mouse duodenum. Mitochondria (*) in Sdhb^+/− duodenum have partial to complete loss of cristae, compared to wild type.