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Mitochondrial Dysfunction And The Role Of Sirt5 In Renal Disease

Haschler, Timo Nicolas; (2020) Mitochondrial Dysfunction And The Role Of Sirt5 In Renal Disease. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Kidney disease is a global health concern with high mortality for which effective therapies are lacking. Accumulating evidence has identified excessive mitochondrial fragmentation causing mitochondrial dysfunction as a central pathologic feature of kidney disease. Recently, the NAD+-dependent lysine desuccinylase/demalonylase sirtuin 5 (SIRT5) has emerged as a key regulator of mitochondrial form and function but its role in the kidney is unknown. Immunostaining of normal human kidneys showed increased expression of SIRT5 in mitochondria-rich tubules. Subsequent immunostaining of murine kidneys from an ischaemic renal injury (IRI) (AKI model) and folic acid nephritis (FAN) (CKD model) model revealed that IRI increased SIRT5 expression, while FAN decreased expression. An in vitro oxygen/nutrient-deprivation (OND) model was developed in human proximal tubular epithelial cells (hPTECs) to mimic in vivo renal ischaemia. OND increased SIRT5 expression in hPTECs. SIRT5 was depleted (by RNAi) and hPTECs were exposed to OND followed by assessment of mitochondrial form and function using confocal/ transmission electron microscopy, Seahorse, FACS and WB. SIRT5 depletion impaired cellular energy metabolism, disrupted mitochondrial fission/fusion dynamics, induced mitochondrial fragmentation and enhanced mitophagy. This effect was exacerbated by OND. SIRT5 depletion also increased mitochondrial swelling and decreased mitochondrial respiration after OND. Sirt5-/- and wild-type mice underwent IRI surgery (40min) (AKI model), or received a single injection of with folic acid (240µg/g BW) or vehicle control (CKD model). IRI and FAN kidneys were harvested after 24h and 14d, respectively, and analysed by qPCR, IHC and WB. Sirt5-/- mice were protected from IRI and showed mildly aggravated injury in the FAN model. Analysis of renal Sirt5-/- mitochondria revealed a reduction in complex II activity, a central driver of reperfusion injury in IRI, hinting that this may be one potential mechanism that alleviates IRI. Mitochondrial function has been shown to be impaired in Sirt5-/- kidneys suggesting that this may have exacerbated FAN. Taken together, the data showed that SIRT5 is an ischaemia-inducible enzyme in murine kidneys and hPTECs. This together with the observation that SIRT5 depletion caused mitochondrial dysfunction in vitro in hPTECs as well as in vivo in murine kidney suggested that the increase in SIRT5 levels is aimed at enhancing mitochondrial function. Loss of SIRT5 alleviated IRI and exacerbated FAN in mice in vivo indicating that impaired mitochondrial function may on one hand reduce acute ischaemic injury, and on the other, aggravate chronic nephrotoxic injury.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Mitochondrial Dysfunction And The Role Of Sirt5 In Renal Disease
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: Mitochondrial dysfunction, Mitophagy, Kidney disease, Renal ischemia, Mitochondrial dynamics, SIRT5
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Medicine
URI: https://discovery.ucl.ac.uk/id/eprint/10098037
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