Genetic inactivation of the translin/trax microRNA-degrading enzyme phenocopies the robust adiposity induced byTranslin(Tsn) deletion

Abstract

Objective: Deletion of Translin (Tsn) from mice induces an unusual metabolic profile characterized by robust adiposity, normal body weight and glucose tolerance.Translin (TN) protein and its partner, trax (TX), form the TN/TX microRNA-degrading enzyme. Since the microRNA system plays a prominent role in regulating metabolism, we reasoned that the metabolic profile displayed by Tsn KO mice might reflect dysregulation of microRNA signaling. Methods:To test this hypothesis, we inserted a mutation, E126A, in Tsnax, the gene encoding TX, that abolishes the microRNA-degrading enzymatic activity of the TN/TX complex. In addition, to help define the cell types that drive the adiposity phenotype, we have also generated mice with floxed alleles of Tsn or Tsnax.Results: Introduction of the E126A mutation in Tsnax does not impair expression of TN or TX proteins or their co-precipitation. Furthermore, these mice display selective increases in microRNAs that match those induced by Tsn deletion, confirming that this mutation in Tsnax inactivates the microRNA-degrading activity of the TN/TX complex. Mice homozygous for the Tsnax (E126A) mutation display a metabolic profile that closely mimics that of Tsn KO mice.Selective deletion of Tsn or Tsnax from either adipocytes or hepatocytes, two candidate cell types, does not phenocopy the elevated adiposity displayed by mice with constitutive Tsn deletion or the Tsnax(E126A) mutation. Furthermore, global, conditional deletion of Tsn in adulthood does not elicit increased adiposity.Conclusion: Taken together, these findings indicate that inactivation of the TN/TX microRNA-degrading enzyme during development is necessary to drive the robust adiposity displayed by Tsn KO mice.Recent studies have strongly implicated the microRNA system in regulating adipose tissue size and function [14][15][16]. For example, conditional deletion of Dicer from adipocytes inhibits lipogenesis in white adipocytes and produces severe depletion of white adipose tissue [17,18]. In previous studies, we have shown that the TN/TX complex can oppose the action of Dicer by degrading pre-microRNAs, thereby preventing their processing into mature microRNAs by Dicer [10]. Thus, these findings suggested that the adiposity displayed by Tsn KO mice could be attributed to increased microRNA signaling due to loss of the TN/TX microRNA-degrading enzyme. To test this hypothesis directly, we have taken advantage of recent studies which have

Increased amphetamine-induced hyperactivity intranslin (Tsn)KO mice is driven by elevated adiposity

“…Mice with floxed alleles of Tsn or Tsnax were generated on a C57BL/6J background using CRISPR/Cas9 technology as described in Fu et al [25]. The following Cre driver or reporter lines were obtained from JAX labs or MMRRC (Drd1-Cre (EY217); Ai9 #007909; DAT-Cre #006660; Adora2a-Cre #036158; Ubiquitin C-CreERT2 #007001).…”

“…In recent studies, we have found that global, conditional deletion of Tsn in adulthood, using tamoxifen-induced activation of the UBC-CreERT2 allele, does not produce increased adiposity [25]. Therefore, we used this manipulation to examine the effect of Tsn deletion on the locomotor response to amphetamine in the absence of increased adiposity.…”