**1. Introduction**

Mitochondria are organelles that fulfill a wide variety of functions in the cell. In addition to being a bioenergetics node, they also serve as signal organelles that communicate to the rest of the cell through different mechanisms. For example, the production of reactive oxygen species (ROS) [1], calcium influx [2], adenosine triphosphate (ATP) levels that regulate adenosine monophosphate protein kinase (AMPK) activation [3], modulation of the immune response through mitochondrial DNA (mtDNA) [4], releasing of cytochrome c orchestrating apoptosis [5], and also through Krebs cycle metabolites [6]; that modulates cell adaptation to different conditions.

The tricarboxylic acid (TCA) cycle, also named the citric acid cycle and Krebs cycle (although this last name can be dissected in the three different cycles: the urea, the glyoxylate, and TCA cycles) was described by Hans Krebs and his colleagues [7]. It is known chiefly for producing electron donors, the reduced form of nicotinamide adenine dinucleotide (NADH), and the reduced form of flavin adenine dinucleotide (FADH2) to feed the electrons transport system (ETS). However, their intermediates also can serve as signal molecules to drive several cell functions.

TCA cycle metabolites were discovered as signal molecules mainly in cancer cells and were defined as oncometabolites that promote tumor progression [8]. However, recent evidence suggests that they are associated with diverse pathologies, including kidney diseases.

Kidneys are highly dependent on mitochondrial function due to their energy demand, particularly by the tubular nephron section, which exerts filtration and reabsorption func-

**Citation:** Jiménez-Uribe, A.P.; Hernández-Cruz, E.Y.; Ramírez-Magaña, K.J.; Pedraza-Chaverri, J. Involvement of Tricarboxylic Acid Cycle Metabolites in Kidney Diseases. *Biomolecules* **2021**, *11*, 1259. https://doi.org/10.3390/ biom11091259

Academic Editor: Liang-Jun Yan

Received: 31 July 2021 Accepted: 23 August 2021 Published: 24 August 2021

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tions. Hence, mitochondrial alterations, such as dynamics (fusion/fission), homeostasis (biogenesis/mitophagy), and bioenergetics, impact on kidney function.

In addition, other metabolic functions of the mitochondrial, such as the TCA cycle, could also be involved in kidney diseases.
