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Abstract Chronic stress has the potential to impair health and may increase the vulnerability for psychiatric disorders. Emerging evidence suggests that specific neurometabolic dysfunctions play a role herein. In mice, chronic social defeat (CSD) stress reduces cerebral glucose uptake despite hyperglycemia. We hypothesized that this metabolic decoupling would be reflected by changes in contact sites between mitochondria and the endoplasmic reticulum, important intracellular nutrient sensors, and signaling hubs. We thus analyzed the proteome of their biochemical counterparts, mitochondria-associated membranes (MAMs) from whole brain tissue obtained from CSD and control mice. This revealed a lack of the glucose-metabolizing enzyme hexokinase 3 (HK3) in MAMs from CSD mice. In controls, HK3 protein abundance in MAMs and also in striatal synaptosomes correlated positively with peripheral blood glucose levels, but this connection was lost in CSD. We conclude that the ability of HK3 to traffic to sites of need, such as MAMs or synapses, is abolished upon CSD and surmise that this contributes to a cellular dysfunction instigated by chronic stress. Key messages Chronic social defeat (CSD) alters brain glucose metabolism CSD depletes hexokinase 3 (HK3) from mitochondria-associated membranes (MAMs) CSD results in loss of positive correlation between blood glucose and HK3 in MAMs and synaptosomes

Cisplatin (CDDP) is commonly used to treat a multitude of tumors including sarcomas, ovarian and cervical cancers. Despite recent investigations allowed to improve chemotherapy effectiveness, the molecular mechanisms underlying the development of CDDP resistance remain a major goal in cancer research. Here, we show that mitochondrial morphology and autophagy are altered in different CDDP resistant cancer cell lines. In CDDP resistant osteosarcoma and ovarian carcinoma, mitochondria are fragmented and closely juxtaposed to the endoplasmic reticulum; rates of mitophagy are also increased. Specifically, levels of the mitophagy receptor BNIP3 are higher both in resistant cells and in ovarian cancer patient samples resistant to platinum-based treatments. Genetic BNIP3 silencing or pharmacological inhibition of autophagosome formation re-sensitizes these cells to CDDP. Our study identifies inhibition of BNIP3-driven mitophagy as a potential therapeutic strategy to counteract CDDP resistance in ovarian carcinoma and osteosarcoma.

Charcot-Marie-Tooth (CMT) disease 4A is an autosomal-recessive polyneuropathy caused by mutations of ganglioside-induced differentiation-associated protein 1 (GDAP1), a putative glutathione transferase, which affects mitochondrial shape and alters cellular calcium homeostasis. Here, we identify the underlying mechanism. We found that patient-derived motoneurons and GDAP1 knockdown SH-SY5Y cells display two phenotypes: more tubular mitochondria and a metabolism characterized by glutamine dependence and fewer cytosolic lipid droplets. GDAP1 interacts with the actin-depolymerizing protein Cofilin-1 in a redox-dependent manner, suggesting a role for actin signaling. Consistently, GDAP1 loss causes less F-actin close to mitochondria, which restricts mitochondrial localization of the fission factor dynamin-related protein 1, instigating tubularity. Changes in the actin cytoskeleton also disrupt mitochondria-ER contact sites. This results in lower mitochondrial calcium levels and inhibition of the pyruvate dehydrogenase complex, explaining the metabolic changes upon GDAP1 loss of function. Together, these findings reconcile GDAP1-associated phenotypes and implicate disrupted actin signaling in CMT4A pathophysiology.

Charcot-Marie-Tooth (CMT) disease 4A is an autosomal-recessive polyneuropathy caused by mutations of ganglioside-induced differentiation-associated protein 1 (GDAP1), a putative glutathione transferase, which affects mitochondrial shape and alters cellular Ca2+ homeostasis. Here, we identify the underlying mechanism. We found that patient-derived motoneurons and GDAP1 knockdown SH-SY5Y cells display two phenotypes: more tubular mitochondria and a metabolism characterized by glutamine dependence and fewer cytosolic lipid droplets. GDAP1 interacts with the actin-depolymerizing protein Cofilin-1 in a redoxdependent manner, suggesting a role for actin signaling. Consistently, GDAP1 loss causes less F-actin close to mitochondria, which restricts mitochondrial localization of the fission factor dynamin-related protein 1, instigating tubularity. Changes in the actin cytoskeleton also disrupt mitochondria-ER contact sites. This results in lower mitochondrial Ca2+ levels and inhibition of the pyruvate dehydrogenase complex, explaining the metabolic changes upon GDAP1 loss of function. Together, these findings reconcile GDAP1-associated phenotypes and implicate disrupted actin signaling in CMT4A pathophysiology.

Mitochondria contain their own genome, mitochondrial DNA (mtDNA), essential to support their fundamental intracellular role in ATP production and other key metabolic and homeostatic pathways. Mitochondria are highly dynamic organelles that communicate with all the other cellular compartments, through sites of high physical proximity. Among all, their crosstalk with the endoplasmic reticulum (ER) appears particularly important as its derangement is tightly implicated with several human disorders. Population-specific mtDNA variants clustered in defining the haplogroups have been shown to exacerbate or mitigate these pathological conditions. The exact mechanisms of the mtDNA background-modifying effect are not completely clear and a possible explanation is the outcome of mitochondrial efficiency on retrograde signaling to the nucleus. However, the possibility that different haplogroups shape the proximity and crosstalk between mitochondria and the ER has never been proposed neither investigated. In this study, we pose and discuss this question and provide preliminary data to answer it. Besides, we also address the possibility that single, disease-causing mtDNA point mutations may act also by reshaping organelle communication. Overall, this perspective review provides a theoretical platform for future studies on the interaction between mtDNA variants and organelle contact sites.

The antiproliferative effect of the naturally occurring polyphenol chlorogenic acid (CGA) was evaluated in combination with either cisplatin or oxaliplatin in human cervical carcinoma cell lines that were either sensitive (A431) or resistant to cisplatin (A431Pt), in order to provide evidence to overcome drug resistance. Cytotoxicity of platinating drugs (IC50 ~ 10−6 - 10−5 M) was enhanced by 1–2 orders of magnitude by increasing incubation times (1, 4, and 24 hours) in the two cell lines. CGA treatment presented low cytotoxicity per se (IC50 ~ 10−4 M at 24 h) if compared with platinum drugs and its activity was similar in A431Pt cells and in their sensitive A431 counterpart. The combination of the platinating drugs with CGA (10−6 - 10−4 M) indicated variable effects on cytotoxicity, ranging from potentiation to various degrees of antagonism (in A431 cells) and no effect (in A431Pt cells). In order to explain the different cytotoxic activity elicited by oxaliplatin and cisplatin in association with CGA, the possible presence of chemical interactions was investigated by HPLC analysis. The drug association with CGA caused evident changes in their chromatographic profile, suggesting occurrence of in vitro chemical interactions.

Resistance to chemotherapeutic drugs is a major problem in cancer treatment. The search for new interventions able to overcome this resistance may involve compounds of natural origin, such as flavonoids, ubiquitously present in many foods. In the present study, the cytotoxic effects and cell cycle modulation of the flavonoid quercetin were investigated in ovarian carcinoma (SKOV3) and osteosarcoma (U2OS) human cell lines and in their cisplatin (CDDP)-resistant counterparts (SKOV3/CDDP and U2OSPt cells, respectively). Quercetin (10–50 μM) caused evident changes in the distribution of cell cycle phases in the CDDP-resistant SKOV3/CDDP ovarian cell line. The levels of cyclin D1 and cyclin B1 were determined by means of Western blot in all cell lines incubated with quercetin (50 μM) for 48 hours. The cyclin D1 expression was significantly decreased following the treatment with quercetin in SKOV3 and U2OSPt cells, but not in SKOV3/CDDP and U2OS cells. The reduction of cyclin D1 level could be linked to the G1/S phase alteration found in quercetin-treated cells. Although cyclin B1 is required for G2/M phase, and despite our observation that quercetin influenced the G2/M phase of cell cycle, the flavonoid did not affect cyclin B1 levels in all cell lines, indicating the involvement of other possible mechanisms. These results suggest that quercetin, exceeding the resistance to CDDP, might become an interesting tool to evaluate cytotoxic activity in combination with chemotherapy drugs.

Fifteen plant polyphenols, including flavonoids, cinnamic acids, coumarins and capsaicin, were investigated for their capacity to suppress cell growth and regulate the cell cycle of in vitro human ovarian carcinoma (2008 cell line) and cervix squamous carcinoma cells (A431), and their cisplatin (CDDP)-resistant subclones (C13 and A431Pt, respectively). Evaluation of the cytotoxic effects of the polyphenols (0.01–100 μM) indicated that especially rhein and quercetin were almost equiactive in wild type and CDDP-resistant cells, indicating lack of cross-resistance with cisplatin. Capsaicin was more potent in CDDP-resistant subclones than in wild type cells. The order of their potencies is flavonoids > anthraquinones > vanilloids > coumarins > phenols, cinnamic acids. The natural phenols which were most cytotoxic (rhein, quercetin and capsaicin) were able to cause the arrest of the cancer cell cycle, suggesting that specific cell cycle regulatory proteins are possibly involved in their intracellular mechanism of action. In particular, the natural compounds were revealed to be more active in CDDP-resistant cells than in wild types, especially inducing apoptotic death.