Tissue heterogeneity of mitochondrial activity, biogenesis and mitochondrial protein gene expression in Buffalo
Authors: Sadeesh E.M , Singla Nancy , Lahamge Madhuri S. , Kumari Sweta , AN Ampadi 
Published: January 2023

Abstract
Background
Cellular metabolism is most invariant processes, occurring in all living organisms which involve mitochondrial proteins from both nuclear and mitochondrial genome. Mitochondrial genome and gene expression has played a central role in the oxidative phosphorylation system biogenesis and metabolism of energy. The mitochondrial DNA (mtDNA) copy number, its protein genes expression and activity in tissues vary between various tissues to fulfill specific energy demands across the tissues. To the yet, this tissue-specific diversity is unaware in terms of mitochondrial biogenesis and protein-coding gene expression in the metabolically active tissue of buffalo. Thus, we assessed the variations in mitochondrial functional assay, mtDNA cellular number, and protein gene expression by investigating six bovine tissues.
Materials & methods
The liver, kidney, heart, muscle, ovary and brain of the same freshly slaughtered buffaloes (n = 3) were investigated for their differences in mitochondrial bioenergetics by measuring the individual OXPHOS complexes and enzymatic activity of citrate synthase in isolated mitochondria. The evaluation of tissue-specific diversity based on the quantification of mitochondrial DNA copy numbers was performed and also comprised an expression study of 13 protein genes encoded by mitochondrial genome.
Results
The investigated tissues showed striking differences in OXPHOS activities and CS-specific activities. The functional activity of individual OXPHOS complex I was significantly higher in the liver compared to muscle and brain. Tissue-dependent differences again reflected on OXPHOS complex III and V activities, with the liver showing significantly the highest specific activities compared to the heart, ovary, and brain. Additionally, there are considerable differences in the CS-specific activity between tissues, with the ovary, kidney, and liver having significantly greater values. Furthermore, we observed the mtDNA copy number was strictly tissue-specific, indicating the distinct bioenergetics and metabolic requirements of various tissues, with muscle and brain tissues exhibiting the highest levels. Moreover, the CS-specific activity also differs markedly between tissues, with significantly higher values for the ovary, kidney, and liver. Further, we observed a strict tissue specificity of mtDNA copy number, reflecting the specific energy and metabolic demands of different tissues, with brain and muscle tissues showing the highest values. Among 13 PCGs expression analyses, mRNA abundances in all genes were differentially expressed among the different tissue.
Conclusion
Overall, our results indicate the existence of a tissue-specific variation in mitochondrial activity, bioenergetics, and protein gene expression of mitochondria among various types of buffalo tissues. This study serves as a critical first stage in gathering vital comparable data about the physiological function of mitochondria in energy metabolism in distinct tissues, laying the groundwork for future mitochondrial based diagnosis and research.