Sexually dimorphic effects of SARM1 deletion on cardiac NAD+ metabolism and function

Abstract

Nicotinamide adenine dinucleotide (NAD⁺) decline is repeatedly observed in heart disease and its risk factors. Although strategies promoting NAD⁺ synthesis to elevate NAD⁺ levels improve cardiac function, whether inhibition of NAD⁺ consumption can be therapeutic is less investigated. In this study, we examined the role of sterile-α and TIR motif containing 1 (SARM1) NAD⁺ hydrolase in mouse hearts, using global SARM1-knockout mice (KO). Cardiac function was assessed by echocardiography in male and female KO mice and wild-type (WT) controls. Hearts were collected for biochemical, histological, and molecular analyses. We found that the cardiac NAD⁺ pool was elevated in female KO mice, but only trended to increase in male KO mice. SARM1 deletion induced changes to a greater number of NAD⁺ metabolism transcripts in male mice than in female mice. Body weights, cardiac systolic and diastolic function, and geometry showed no changes in both male and female KO mice compared with WT counterparts. Male KO mice showed a small, but significant, elevation in cardiac collagen levels compared with WT counterparts, but no difference in collagen levels was detected in female mice. The increased collagen levels were associated with greater number of altered profibrotic and senescence-associated inflammatory genes in male KO mice, but not in female KO mice.NEW & NOTEWORTHY We examined the effects of SARM1 deletion on NAD⁺ pool, transcripts of NAD⁺ metabolism, and fibrotic pathway for the first time in mouse hearts. We observed the sexually dimorphic effects of SARM1 deletion. How these sex-dependent effects influence the outcomes of SARM1 deficiency in male and female mice in responses to cardiac stresses warrant further investigation. The elevation of cardiac NAD⁺ pool by SARM1 deletion provides evidence that targeting SARM1 may reverse disease-related NAD⁺ decline.

Keywords: NAD metabolism; SARM1; cardiac dysfunction; sex differences.

Figure 1.

SARM1 deficiency increases cardiac NAD⁺ levels and induces sex-based changes in NAD⁺ consumption transcripts. Quantitative PCR analysis was used to confirm deletion of Sarm1. A: Sarm1 transcript levels. NAD⁺ and NADH levels were quantified by a colorimetric assay. B: NAD⁺ pool was measured in mouse hearts. Quantitative PCR analyses were used to assess transcript expression of NAD⁺ consumption enzymes in the hearts of male and female wild-type (WT) and SARM1-KO mice. Cd38 (C), Bst1 (D), Parp1 (E), Sirt1 (F), Sirt5 (G), Sirt6 (H), and Sirt7 (I) transcript levels were measured. J: heatmap summarizing NAD⁺ consumption gene expression. Expression data are represented as fold-change with respect to WT mice of same sex. *P < 0.05, **P < 0.01 vs. WT; n = 6 per group. Blue charts, male mice data; red charts, female mice data. On the heatmap, gene names with underlined text signify P < 0.05 vs. WT. KO, knockout; mRNA, messenger RNA; NAD⁺, nicotinamide adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide; PCR, polymerase chain reaction; SARM1, sterile-α and TIR motif containing 1.

Figure 2.

SARM1 deficiency changes the mRNA expression of NAD⁺ synthesis enzymes in male mice, but not in female mice. Quantitative PCR analyses were used to assess transcript expression of NAD⁺ synthesis enzyme transcripts in the hearts of male and female wild-type (WT) and SARM1-KO mice. Relative mRNA levels of Nampt (A), Nmnat2 (B), Nmnat3 (C), Nmrk2 (D), and Qprt (E) were measured. F: heatmap summarizing NAD⁺ synthesis gene expression. Expression data were represented as fold-change with respect to WT mice of same sex. *P < 0.05, **P < 0.01 vs. WT; n = 6 per group. Blue charts, male mice data; red charts, female mice data. On the heatmap, gene names with underlined text signify P < 0.05 vs. WT. KO, knockout; mRNA, messenger RNA; NAD⁺, nicotinamide adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide; PCR, polymerase chain reaction; SARM1, sterile-α and TIR motif containing 1.

Figure 3.

SARM1 deficiency does not change body weight, cardiac function, and geometry in male and female mice at baseline. Body weight and cardiac function by echocardiography were measured in male and female, young wild-type (WT), and SARM1-KO mice. Body weight (A), fractional shortening (FS; B), early-to-late ratio of peak diastolic velocity (E′/A′ ratio; C), and left ventricular internal dimension (end-diastolic; LVID;d; D) were measured. Blue charts, male mice data; red charts, female mice data; n = 6 per group. BW, body weight; KO, knockout; SARM1, sterile-α and TIR motif containing 1.

Figure 4.

SARM1 deficiency induces sex-based changes in the cardiac expression of profibrotic and prosenescence genes in mice. A: percent collagen was quantified by Masson-trichrome staining of heart tissue sections. Quantitative PCR analyses were used to assess transcript expression of profibrotic and prosenescence genes in the hearts of male and female, wild-type (WT), and SARM1-KO mice. Relative mRNA levels of Ctgf (B), Tgfb2 (C), Fn1 (D), Col1a1 (E), Gdf15 (F), p21/Cdkn1a (G), Trp53 (H), and Cxcl1 (I). J: heatmap summarizing profibrotic and prosenescence gene expression. Expression levels were normalized to WT mice of the respective sex. *P < 0.05, **P < 0.01 vs. WT; n = 6 per group. Blue charts, male mice data; red charts, female mice data. On the heatmap, gene names with underlined text signify P < 0.05 vs. WT. KO, knockout; mRNA, messenger RNA; PCR, polymerase chain reaction; SARM1, sterile-α and TIR motif containing 1.