Decreased expression of mitochondrial frataxin (FXN) causes Friedreich's ataxia (FRDA), a neurodegenerative disease with type 2 diabetes (T2D) as severe comorbidity. Brown adipose tissue (BAT) is a mitochondria-enriched and antidiabetic tissue that turns excess energy into heat to maintain metabolic homeostasis. Here we report that the FXN knock-in/knock-out (KIKO) mouse shows hyperlipidemia, reduced energy expenditure and insulin sensitivity, and elevated plasma leptin, recapitulating T2D-like signatures. FXN deficiency leads to disrupted mitochondrial ultrastructure and oxygen consumption as well as lipid accumulation in BAT. Transcriptomic data highlights cold intolerance in association with iron-mediated cell death (ferroptosis). Impaired PKA-mediated lipolysis and expression of genes controlling mitochondrial metabolism, lipid catabolism and adipogenesis were observed in BAT of KIKO mice as well as in FXN-deficient T37i brown and primary adipocytes. Significant susceptibility to ferroptosis was observed in adipocyte precursors that showed increased lipid peroxidation and decreased glutathione peroxidase 4. Collectively our data point to BAT dysfunction in FRDA and suggest BAT as promising therapeutic target to overcome T2D in FRDA.
Frataxin deficiency is the pathogenic cause of Friedreich’s Ataxia, an autosomal recessive disease characterized by the increase of oxidative stress and production of free radicals in the cell. Although the onset of the pathology occurs in the second decade of life, cognitive differences and defects in brain structure and functional activation are observed in patients, suggesting developmental defects to take place during fetal neurogenesis. Here, we describe impairments in proliferation, stemness potential and differentiation in neural stem cells (NSCs) isolated from the embryonic cortex of the Frataxin Knockin/Knockout mouse, a disease animal model whose slow-evolving phenotype makes it suitable to study pre-symptomatic defects that may manifest before the clinical onset. We demonstrate that enhancing the expression and activity of the antioxidant response master regulator Nrf2 ameliorates the phenotypic defects observed in NSCs, re-establishing a proper differentiation program.
Background: Friedreich’s ataxia (FRDA) is a neurodegenerative disease characterized by early mortality due to hypertrophic cardiomyopathy. FRDA is caused by reduced levels of frataxin (FXN), a mitochondrial protein involved in the synthesis of iron-sulphur clusters, leading to iron accumulation at the mitochondrial level, uncontrolled production of reactive oxygen species and lipid peroxidation. These features are also common to ferroptosis, an iron-mediated type of cell death triggered by accumulation of lipoperoxides with distinct morphological and molecular characteristics with respect to other known cell deaths. Scope of review: Even though ferroptosis has been associated with various neurodegenerative diseases including FRDA, the mechanisms leading to disease onset/progression have not been demonstrated yet. We describe the molecular alterations occurring in FRDA that overlap with those characterizing ferroptosis. Major conclusions: The study of ferroptotic pathways is necessary for the understanding of FRDA pathogenesis, and anti-ferroptotic drugs could be envisaged as therapeutic strategies to cure FRDA.
Low-protein/high-carbohydrate (LPHC) diet has been suggested to promote metabolic health and longevity in adult humans and animal models. However, the complex molecular underpinnings of how LPHC diet leads to metabolic benefits remain elusive. Through a multi-layered approach, here we observed that LPHC diet promotes an energy-dissipating response consisting in the parallel recruitment of canonical and non-canonical (muscular) thermogenic systems in subcutaneous white adipose tissue (sWAT). In particular, we measured Ucp1 induction in association with up-regulation of actomyosin components and several Serca (Serca1, Serca2a, Serca2b) ATPases. In beige adipocytes, we observed that AMPK activation is responsible for transducing the amino acid lowering in an enhanced fat catabolism, which sustains both Ucp1-and Serca-dependent energy dissipation. Limiting AMPK activation counteracts the expression of brown fat and muscular genes, including Ucp1 and Serca, as well as mitochondrial oxidative genes. We observed that mitochondrial reactive oxygen species are the upstream molecules controlling AMPK-mediated metabolic rewiring in amino acid-restricted beige adipocytes. Our findings delineate a novel metabolic phenotype of responses to amino acid shortage, which recapitulates some of the benefits of cool temperature in sWAT. In conclusion, this highlights LPHC diet as a valuable and practicable strategy to prevent metabolic diseases through the enhancement of mitochondrial oxidative metabolism and the recruitment of different energy dissipating routes in beige adipocytes.
Since online publication of this article, the authors noticed that there was a basic citation error in PubMed citation data. Specifically, the name of the author “Piergiorgio La Rosa” is cited as "Rosa P” in the PubMed citation, when it should be “La Rosa P”, “La Rosa” being the surname and “Piergiorgio” the name of the author.
26Decreased expression of the mitochondrial protein frataxin (FXN) causes Friedreich's ataxia 27 (FRDA). FRDA is a neurodegenerative disease also characterized by systemic metabolic alterations 28 that increase the risk of developing type 2 diabetes thus aggravating FRDA prognosis. Brown adipose 29 tissue (BAT) is a mitochondria-enriched and anti-diabetic tissue that, in addition to its 30 thermoregulatory role, turns excess energy into heat to maintain energy balance. Here we report that 31FXN knock-in/knock-out (KIKO) mouse shows reduced energy expenditure and VO2, 32 hyperlipidemia, decreased insulin sensitivity and enhanced circulating levels of leptin, recapitulating 33 diabetes-like signatures. FXN deficiency leads to alteration of mitochondrial structure and oxygen 34 consumption, decreased lipolysis and lipid accumulation in BAT. Transcriptomic data highlighted a 35 blunted thermogenesis response, as several biological processes related to thermogenesis (e.g. 36 response to temperature stimuli, mitochondrial gene transcription, triglyceride metabolism, 37 adipogenesis) resulted affected in BAT of KIKO mice upon cold exposure. Decreased adaptation to 38 cool temperature in association with limited PKA-mediated lipolysis and downregulation of the 39 expression of the genes controlling mitochondrial metabolism and lipid catabolism were observed in 40 KIKO mice. T37i brown adipocytes and primary adipocytes with FXN deficiency showed reduced 41 thermogenesis and adipogenesis markers respectively recapitulating the molecular signatures 42 detected in KIKO mice. 43 Collectively our data point to BAT dysfunction in FRDA and suggest BAT as a promising target to 44 overcome metabolic complications in FRDA. 45 46
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