Identification of a Novel Gene for Diabetic Traits in Rats, Mice, and Humans

Abstract

The genetic basis of type 2 diabetes remains incompletely defined despite the use of multiple genetic strategies. Multiparental populations such as heterogeneous stocks (HS) facilitate gene discovery by allowing fine mapping to only a few megabases, significantly decreasing the number of potential candidate genes compared to traditional mapping strategies. In the present work, we employed expression and sequence analysis in HS rats (Rattus norvegicus) to identify Tpcn2 as a likely causal gene underlying a 3.1-Mb locus for glucose and insulin levels. Global gene expression analysis on liver identified Tpcn2 as the only gene in the region that is differentially expressed between HS rats with glucose intolerance and those with normal glucose regulation. Tpcn2 also maps as a cis-regulating expression QTL and is negatively correlated with fasting glucose levels. We used founder sequence to identify variants within this region and assessed association between 18 variants and diabetic traits by conducting a mixed-model analysis, accounting for the complex family structure of the HS. We found that two variants were significantly associated with fasting glucose levels, including a nonsynonymous coding variant within Tpcn2. Studies in Tpcn2 knockout mice demonstrated a significant decrease in fasting glucose levels and insulin response to a glucose challenge relative to those in wild-type mice. Finally, we identified variants within Tpcn2 that are associated with fasting insulin in humans. These studies indicate that Tpcn2 is a likely causal gene that may play a role in human diabetes and demonstrate the utility of multiparental populations for positionally cloning genes within complex loci.

Diversity Outbred Mice at 21: Maintaining Allelic Variation in the Face of Selection

“…Multi-parent crosses have become increasingly popular for QTL studies (Gnan et al 2014; Huang et al 2014; Tsaih et al 2014; Dell’Acqua et al 2015) due to the idiosyncratic histories of existing reference populations and the desire to meet ideal properties of uniform allele frequencies, randomized assortment, and recombination. Here, we demonstrate the need for proactive monitoring and potential corrective measures to maintain the utility of populations like the DO.…”

Function and dysfunction of two-pore channels

“…If loss of TPC function precipitates liver dysfunction (59), then it follows that TPC activators might prove beneficial in this disorder just as synthetic activators of TRPMLs can correct trafficking defects associated with hypomorphic function of TRPML1 in the lysosomal storage disorder mucolipidosis IV (93). Potential links between TPCs and Alzheimer's disease (94), diabetes (95), and obesity (96) Fig. 3.…”

Two-pore channels (TPCs): Novel voltage-gated ion channels with pleiotropic functions

“…40,67 Regarding TPC2, RNA gel blot analysis showed the same tissue distribution as TPC1 in mice, although with lower expression, 60 and, in human, TPC2 was detectable in lung, placenta, small intestine, liver, kidney, spleen, thymus, colon, skeletal muscle, heart and brain. 4 RT-PCR showed TPC2 mRNA expression in pancreas in mice, 21 in liver and heart in rats, 40,68 and in the human heart. 40,67 Protein expression of TPC2 was detectable by protein gel blot in liver in mice, 44 and in human and rat hearts, 40,67 and by immunofluorescence in human pancreatic b-cells.…”