Mitochondrial Fusion As A Regulatory Event Of Synthesis And Transport Of Lipid Molecules

HELFENBERGER KATIA E.; CASTILLO ANA FERNANDA; MELE PABLO; DATTILO MELINA; MALOBERTI PAULA; PODESTA ERNESTO JORGE; PODEROSO CECILIA

Busan

Congreso; 45th World Chemistry Congress; 2015

IUPAC

Chemically, cholesterol is an organic molecule consisting of a cyclopentaneperhydrophenantrene core, an hydroxyl group in carbon 3, a lateral chain of 8 carbon atoms, a double bond in C-5 position and five methyl groups. It belongs to the sterols family and it is the precursor molecule for all steroid hormones, including glucocorticoids, androgens, estrogen and mineralocorticoids. Mitochondria and the endoplasmic reticulum (ER) are cholesterol-poor organelles with estimates ranging from 0.5% to 3% of the content found in plasma membrane. Cholesterol can be transported into mitochondria by specific mitochondrial protein carriers like the Steroidogenic Acute Regulatory (StAR) protein, in steroidogenic tissues (1). Cholesterol transport to the inner mitochondrial membrane mediated by StAR, is the first and rate-limiting step in biosynthesis of all steroids. Different steroidogenic enzymes are localized between the mitochondria and the ER to produce the final steroid hormone.The question that arises is whether lipophilic steroids can shuttle between these membranous structures without reaching hydrophilic cytoplasm. Mitochondrial dynamics (known as fusion/fission) allows mitochondrial replication, selective elimination of depolarized mitochondria via mitophagy and propagation of intra-mitochondrial calcium waves (2). Mitofusin (Mfn) 1 and 2 are implicated in the modulation of mitochondria?mitochondria and ER?mitochondria interactions. Hormone stimulation through PKA (Protein Kinase cAMP-dependent) activation triggers mitochondrial changes into tubular-shaped structures (fusion-like) in MA-10 Leydig cells (3). Despite the importance of mitochondrial fusion in several metabolic and hormonal conditions, there are no data of its role in steroidogenesis mediated by PKC (Protein Kinase Ca2+-dependent) pathway. In the present work, we aimed to study the role of mitochondrial fusion in the regulation of aldosterone synthesis by Angiotensin II (Ang II) and cAMP. Aldosterone is the major mineralocorticoid involved in maintaining fluid and electrolyte balance in all mammals, working mainly through PKC/Ca2+ signaling pathway. We analyzed Ang II and cAMP stimulation effects in glomerulosa derived cells (H295R adrenocortical cells). We demonstrated here that mitochondrial fusion is required for steroid production and StAR protein induction in H295R cells. Ang II and cAMP stimulation promoted a shift between punctuated to tubular/elongated (fusion) mitochondrial shape. Mfn2 expression is upregulated after Ang II or cAMP stimulation and Mfn2 inhibition by knockdown (small interference RNA) is sufficient to impair steroid biosynthesis (without siRNA-Mfn2: C: 0.20±0.06; Ang II: 0.48±0.10; cAMP: 0.70±0.13; with siRNA-Mfn2: C: 0.24±0.08; Ang II: 0.29±0.07; cAMP: 0.50±0.10; ng/ml Aldosterone P