Mitochondrial Metabolism Meets LncRNA Biology: The Role of uc.173 in Intestinal Homeostasis

Mitochondria play an important role in intestinal homeostasis. They provide the energy required for epithelial renewal and support barrier integrity through the regulation of tight junctions.¹ In addition, mitochondria integrate nutrient, redox, and microbial-derived signals to influence intestinal epithelial cell (IEC) fate, secretory activity, and stress responses.² Mitochondrial dysfunction is increasingly recognized as a hallmark of diverse intestinal disorders and is frequently observed in patients with inflammatory bowel disease (IBD), sepsis, and ischemia-reperfusion injury, where it contributes to delayed mucosal healing.² Despite its clinical importance, the mechanisms of regulating intestinal mitochondrial biogenesis remain poorly understood.

In this issue of Cellular and Molecular Gastroenterology and Hepatology, Xiao et al³ present compelling evidence that the long noncoding RNA (lncRNA) uc.173, transcribed from an ultraconserved genomic region (T-UCR), plays a pivotal role in regulating mitochondrial metabolism and intestinal mucosal growth through the miR-29b/PGC-1α axis. Their study integrates an IEC-specific in vivo knockout model with ex vivo organoid assays, as well as in vitro molecular mechanistic studies using IEC cell lines. They identify uc.173, a T-UCR, as a promising therapeutic target for restoring mitochondrial function and enhancing mucosal regeneration in intestinal disorders. These findings shed light on the upstream signaling pathways controlling mitochondrial metabolism and biogenesis, thereby influencing intestinal epithelial homeostasis.

LncRNAs have emerged as crucial regulators of gene expression in intestinal homeostasis and disease.4, 5, 6, 7 Among them, T-UCRs represent a unique class of lncRNAs that are completely conserved across human, mouse, and rat genomes.⁸ T-UCRs, which are dynamically regulated in cancer, inflammation, hypoxia, and starvation, influence chromatin remodeling, transcription, and post-transcriptional control.⁸ Prior work from this research team demonstrated that uc.173 is downregulated in inflamed intestinal mucosa from patients with IBD, whereas increased uc.173 expression enhances mucosal repair and barrier function; however, the underlying molecular mechanism remained unclear before this study.^1,9

The new study by Xiao et al³ illustrates how uc.173 is a novel regulator of mitochondrial metabolism in IECs. Silencing uc.173 reduces the expression of key mitochondrial proteins, including PGC-1α, PHB1, PHB2, SDHA, and COXs, resulting in mitochondrial dysfunction characterized by reduced respiration, ATP production, and spare respiratory capacity. Mechanistically, uc.173 acts as a molecular decoy for miR-29b, thereby preventing miR-29b mediated translational repression of PGC-1α, the key transcriptional regulator of mitochondrial biogenesis. This post-transcriptional regulation ensures adequate mitochondrial biogenesis to meet the high energy demands of the continuously renewing gut epithelium. In addition to direct effects on mitochondrial metabolism, uc.173 influences Paneth cells in the intestinal stem cell (ISC) niche, which is crucial for stem cell maintenance and epithelial turnover.¹⁰ Loss of uc.173 leads to Paneth cell dysfunction, reduced WNT3 and NOTCH2 levels, and impaired ISC proliferation, while goblet cell differentiation remains unaffected. These findings indicate a selective regulatory role of uc.173 in sustaining ISC niche integrity and epithelial growth. Furthermore, uc.173 deficiency results in decreased expression of tight junction proteins (Occludin, Claudin-1, JAM-A, ZO-1), compromising gut barrier function. These findings support the role of uc.173 as a central regulator of intestinal epithelial homeostasis. Together, the discovery that uc.173 sustains mitochondrial metabolism and ISC niche function provides a new mechanistic framework for understanding intestinal homeostasis. Therapeutic strategies aimed at restoring mitochondrial function through the mitochondrial activator Mito-Tempo or overexpression of PGC-1α rescue mucosal growth in uc.173-deficient organoids, underscoring the therapeutic potential of the uc.173/miR-29b/PGC-1α axis. Given that T-UCRs are evolutionarily conserved, these findings may have translational relevance for human disease. Modulating uc.173 expression could represent a novel approach to promote mucosal healing in patients with IBD, sepsis, or post-surgical injuries.

Notably, an innovative technical aspect of this study is the dissection of the in vivo role of uc.173 using a novel CRISPR-based mouse model.¹¹ The authors combined intestinal epithelium-specific Cas9 (IE-Cas9) expression with lentiviral delivery of uc.173-targeting sgRNA (lenti-sgRNA-uc.173).³ Administration of lenti-sgRNA-uc.173 induced a targeted loss-of-function mutation of uc.173, specifically in the intestinal epithelium, leaving other organs unaffected. This CRISPR-Cas9-based tissue-specific and transient gene-editing approach resulted in robust downregulation of uc.173 in intestinal epithelial cells, with maximal knockdown efficiency observed on day 7 and sustained suppression for at least 15 days. Although minor inter-animal variability in editing efficiency was noted, this approach represents a powerful and versatile platform for investigating the in vivo function of target genes, including protein coding genes and lncRNAs, with both tissue and temporal specificity.

Although this study enhances our understanding of uc.173 in regulating mitochondrial metabolism and intestinal epithelial renewal, several questions remain unanswered and are open to further exploration. First, the IEC-specific CRISPR-Cas9 approach, while innovative, yielded transient gene-editing efficiency, which may not fully capture long-term consequences of uc.173 loss. Second, although the uc.173/miR-29b/PGC-1α axis provides a mechanistic link, additional pathways and cofactors may contribute to the broader network of mitochondrial regulation and mucosal homeostasis. Finally, functional outcomes such as systemic inflammation or host-microbe interactions were not explored, leaving unknown questions about the translational relevance of targeting uc.173 in critical illness or inflammatory diseases. Addressing these issues in future studies will be essential to fully establish the therapeutic potential of uc.173 in human.

In summary, this study by Xiao and colleagues demonstrates a paradigm in which the T-UCR uc.173 links mitochondrial metabolism to intestinal epithelial renewal and homeostasis. By acting as a miRNA decoy for miR-29b, uc.173 enhances PGC-1α translation, supporting mitochondrial function and Paneth cell activity. These findings not only advance our understanding of T-UCR biology but also highlight novel therapeutic approaches for intestinal disorders with impaired mucosal growth.