The production of therapeutic recombinant toxins requires careful host cell selection. Bacteria, yeast, and mammalian cells are common choices, but no universal solution exists. Achieving the delicate balance in toxin production is crucial due to potential self-intoxication. Recombinant toxins from various sources find applications in antimicrobials, biotechnology, cancer drugs, and vaccines. “Toxin-based therapy” targets diseased cells using three strategies. Targeted cancer therapy, like antibody–toxin conjugates, fusion toxins, or “suicide gene therapy”, can selectively eliminate cancer cells, leaving healthy cells unharmed. Notable toxins from various biological sources may be used as full-length toxins, as plant (saporin) or animal (melittin) toxins, or as isolated domains that are typical of bacterial toxins, including Pseudomonas Exotoxin A (PE) and diphtheria toxin (DT). This paper outlines toxin expression methods and system advantages and disadvantages, emphasizing host cell selection’s critical role.

Neurodegenerative diseases (NDs) are the most prevalent age-associated disorders, characterized by progressive neuronal loss and cognitive decline. Mitochondrial dysfunction is strictly associated with NDs and represent one of the hallmarks of these disorders, with neurological syndromes frequently representing the primary clinical manifestations of mitochondrial abnormalities. As central regulators of cellular bioenergetics, mitochondria play a pivotal role in both the physiological maintenance and pathogenesis of disease by different regulatory approaches. One of these, microRNAs (miRNAs), a class of small non-coding RNAs, are well-established regulators of gene expression across different biological pathways. These miRNAs were usually investigated within the cytoplasmic context, but recent discoveries have revealed the presence of these miRNAs in different parts of mitochondria, where they contribute to the regulation of gene expression and metabolic activity. These mitochondrial-localized miRNAs, termed mito-MiRNA, may originate from either nuclear or mitochondrial genomes and have been shown to modulate the translational machinery of the cells. Despite extensive research on cytoplasmic miRNAs, the functional roles of mito-MiRNA remain poorly understood, particularly in the context of neurodegenerative disorders. Based on these findings, this review aims to synthesize emerging evidence on the involvement of mito-MiRNA in in one of most prevalent neurodegenerative diseases—Parkinson’s disease (PD).